Showing papers in "Medical and Veterinary Entomology in 1998"
TL;DR: The classification of the mosquito esterases in the context of classical esterase nomenclature is covered and implications of information on the ester enzyme amplicons are discussed in relation to the evolution and migration of insecticide resistance in Culex.
Abstract: The major mechanism of organophosphorus insecticide resistance in Culex mosquitoes involves the elevation of one or more esterases. The general mechanism underlying this resistance is the amplification of the structural genes. This review covers the classification of the mosquito esterases in the context of classical esterase nomenclature. The function of the amplified esterases and the structure of the amplified DNA on which they occur are also described. Implications of information on the esterase amplicons are discussed in relation to the evolution and migration of insecticide resistance in Culex.
330 citations
TL;DR: The purpose of this study was to define the vector of AVL in the region and to highlight the areas considered to be hyperendemic, as well as the urbanization of the disease.
Abstract: Leishmania chagasi (Cunha & Chagas), the aetiologic agent of American visceral leishmaniasis (AVL), is transmitted by Lutzomyi longipalpis(Lutz & Neiva) throughout the Americas, from Northern Argentina to Southern Mexico (Arias et al. 1996b). In at least one previously reported case, another species of sand fly,Lu. evansi(Nuñez-Tovar), has been reported to be a suspected vector, in a specific focus of the disease, in San Andrés de Sotavento, Department of Cordoba, Colombia (Travi et al., 1990) Classically, in Brazil, AVL has been a major problem in the states in the north-east of the country, specifically in Ceara ́ and Bahia (Deane & Deane, 1962), manifesting itself in a pattern suggestive of a 10-year cycle (I. A. Sherlock, personal communication, Akhavan, 1996). During the past few years, many countries have witnessed the re-emergence of AVL, as well as the urbanization of the disease (Ariaset al. 1996a). What we have witnessed in Corumbáand Lada ́rio, Mato Grosso do Sul State, Brazil is an example of what is occurring in many cities. Here, canines infected withLe. chagasiwere first reported in 1983 after a serological survey was carried out (Rego et al., 1983), even though human cases of AVL had been reported as early as 1980 in Corumba ́’s hospitals and health centres. As can be seen in Table 1, in a city with a population of c. 96 000 the first human cases were reported in 1993 and since then, there has been an increase in the number of cases. Even though this area is considered to be hyperendemic (Anon, 1994), previous entomological studies (Galati et al., 1985, 1989) did not reveal the presence of Lu. longipalpis. Control interventions were initiated in midto late-1995. However, they were not sustained, and the coverage was only μ 45%. The purpose of this study was to define the vector of AVL in the region.
192 citations
TL;DR: This poster aims to demonstrate the efforts towards in-situ applicability of EMMARM, as to provide real-time information about the behaviour of insects in the environment.
Abstract: Pyrethroid resistance was investigated in thirty-three samples of Culex quinquefasciatus Say from twenty-five cities in Cote d'Ivoire and Burkina Faso. Permethrin resistance ratios at LC50 ranged from 9.5- to 82-fold in Cote d'Ivoire and from 17- to 49-fold in Burkina Faso. For deltamethrin, resistance ratios were lower and ranged from nine to thirty-eight in both countries. A strain was selected with permethrin to investigate resistance mechanisms. After forty-two generations of selection, permethrin resistance level reached 3750-fold, but deltamethrin resistance remained unexpectedly unchanged. This indicated that a specific mechanism was involved in permethrin resistance. Synergist assays and biochemical tests indicated that resistance was partly due to P450-dependent oxidases. A target site insensitivity (kdr) was also involved, associated with DDT cross resistance and a dramatic loss of permethrin knockdown effect on adults. This resistance should be taken into consideration when planning the use of pyrethroid-impregnated materials in urban areas, as Culex is by far the main source of nuisance. Any failure in nuisance control due to resistance is likely to demotivate people in using impregnated materials.
186 citations
TL;DR: Biochemical assays showed that the DDT resistance was caused by elevated levels of glutathione S‐transferase (GST) activity leading to increased rates of metabolism of DDT to DDE, suggesting that this is the only majorDDT resistance mechanism in this population.
Abstract: .A high level of DDT resistance and low levels of resistance to organophosphorus, carbamate and pyrethroid insecticides were detected by discriminating dose assays in field populations of Anopheles albimanus in Chiapas, southern Mexico, prior to a large-scale resistance management project described by Hemingway et al. (1997) . Biochemical assays showed that the DDT resistance was caused by elevated levels of glutathione S-transferase (GST) activity leading to increased rates of metabolism of DDT to DDE. The numbers of individuals with elevated GST and DDT resistance were well correlated, suggesting that this is the only major DDT resistance mechanism in this population.
The carbamate resistance in this population is conferred by an altered acetylcholinesterase (AChE) -based resistance mechanism. The level of resistance observed in the bioassays correlates with the frequency of individuals homozygous for the altered AChE allele. This suggests that the level of resistance conferred by this mechanism in its heterozygous state is below the level of detection by the WHO carbamate discriminating dosage bioassay.
The low levels of organophosphate (OP) and pyrethroid resistance could be conferred by either the elevated esterase or monooxygenase enzymes. The esterases were elevated only with the substrate pNPA, and are unlikely to be causing broad spectrum OP resistance. The altered AChE mechanism may also be contributing to the OP but not the pyrethroid resistance.
Significant differences in resistance gene frequencies were obtained from the F1 mosquitoes resulting from adults obtained by different collection methods. This may be caused by different insecticide selection pressures on the insects immediately prior to collection, or may be an indication that the indoor- and outdoor-resting A. albimanus collections are not from a randomly mating single population. The underlying genetic variability of the populations is currently being investigated by molecular methods.
182 citations
TL;DR: The impact of permethrin‐impregnated bednets on resting and feeding behaviour of mosquito vectors of Wuchereria bancrofti, causing human lymphatic filariasis was studied in six pairs of villages before and after intervention.
Abstract: The impact of permethrin-impregnated bednets on resting and feeding behaviour of mosquito vectors of Wuchereria bancrofti, causing human lymphatic filariasis was studied in six pairs of villages (treated and untreated) before and after intervention. The study villages were in Kwale District, near the coast of Kenya, where Bancroftian filariasis is highly endemic, transmitted by a combination of both anopheline and culicine mosquito vectors. Mosquitoes were collected weekly in each village, indoors (using pyrethrum spray catches) and outdoors (using pit traps) during 3–4 months following the long rainy season. Of the filariasis vector species of mosquitoes collected in 1994 before intervention, 33.6% were members of the Anopheles gambiae complex, 30% were An. funestus and 36.4% were Culex quinquefasciatus. PCR analysis of the An. gambiae complex species collected in 1995 demonstrated that 98.5% were An. gambiae sensu stricto, 1% An. arabiensis and 0.5% An. merus.
Introduction of impregnated bednets in 1995 significantly reduced the number of indoor-resting An. gambiae s.l. by 94.6% and An. funestus by 96.7%, but there was no change in the number of Cx quinquefasciatus collected indoors. The number of outdoor-resting An. gambiae s.l. was significantly reduced, whereas densities of An. funestus and Cx quinquefasciatus remained unaffected outdoors. ELISA analysis of mosquito bloodmeals showed a shift from human to animal feeding after the introduction of treated nets. The human blood index (HBI) for indoor resting Cx quinquefasciatus was reduced from 93.1% to 14.4%. Vector potential based on the HBI and mosquito density was estimated to be reduced by 99% for An. gambiae s.l., 98% for An. funestus and 97% for Cx quinquefasciatus and vectorial capacity would be suppressed even more by the impact on the vector survival rates (not measured). These results suggest that permethrin-impregnated bednets give effective personal protection against transmission of W. bancrofti by An. gambiae, An. funestus and Cx quinquefasciatus in East Africa.
172 citations
TL;DR: The results showed that changes in environment, fauna and host availability may result in modification of tsetse feeding patterns, and Suidae were also important hosts for Glossina pallidipes.
Abstract: An enzyme-linked immunosorbent assay (ELISA) was developed to identify the origin of vertebrate blood in the guts of 29 245 wild-caught flies of eleven Glossina species from various ecological zones of Africa. Depending on the quality of the bloodmeal samples, 62.8% of the samples were identified and could be assigned to a host-group (e.g. ruminant), family (e.g. Bovidae) or species (e.g. Bos spp.). A total of 13 145 samples (44.9%) was identifiable up to the species level. With a few exceptions, the present results are in agreement with earlier published reports. Glossina austeni and G. fuscipleuris seemed to have a distinct feeding preference for Suidae (mainly bushpig). Glossina morsitans ssp. fed mainly on Suidae (mainly warthog), although local variations were observed and in some areas hippopotamus or ruminants replaced the warthog as the main host. Bushbuck seemed to be the principal food source for G. longipalpis and G. fusca. Glossina pallidipes fed mainly on ruminants (buffalo, bushbuck and cattle) but, depending on host availability and location, Suidae were also important hosts. Hippopotamus was identified as the main source of bloodmeals for G. brevipalpis. The main hosts for G. longipennis were Suidae (mainly bushpig) and not rhinoceros as had been reported 40 years earlier. The opportunistic feeding behaviour of the palpalis tsetse group was confirmed. The results showed that changes in environment, fauna and host availability may result in modification of tsetse feeding patterns.
162 citations
TL;DR: The prevalence of infection in the three feeding stages of I. ricinus indicated that granulocytic Ehrlichiae are transmitted transstadially with no, or inefficient, transovarial transmission, and demonstration, for the first time, of GE infection in engorged Ixodes trianguliceps ticks and blood collected from wild rodents suggests that European wild rodents are competent reservoirs.
Abstract: The prevalence of infection with Ehrlichiae of the Ehrlichia phagocytophila genogroup (the granulocytic Ehrlichiae), in questing Ixodes ricinus ticks of U.K. upland and woodland habitats, was investigated by PCR. The prevalence of infection in the three feeding stages of I. ricinus indicated that granulocytic Ehrlichiae are transmitted transstadially with no, or inefficient, transovarial transmission. The presence of infected ticks in both habitats indicates that endemic cycles of granulocytic Ehrlichia (GE) infection are maintained by both domesticated sheep and by wild reservoirs, and coexist with endemic cycles of Borrelia burgdorferi infection. Moreover, demonstration, for the first time, of GE infection in engorged Ixodes trianguliceps ticks and blood collected from wild rodents, suggests that European wild rodents are competent reservoirs. GE infection prevalence in nymphal and adult I. ricinus was significantly greater in uplands than woodlands, which is consistent with ticks of all three feeding stages feeding on reservoir-competent sheep in uplands. In one woodland studied, pheasants are important hosts for nymphal I. ricinus but are incompetent or inefficient reservoirs, so reducing GE infection prevalence in I. ricinus ticks in this habitat. 16S rRNA sequences of GE from ticks of these U.K. habitats, showed a high degree of homology with those of granulocytic Ehrlichiae isolated from humans, but also showed some evidence of genetic diversity of granulocytic ehrlichiae in the U.K. The implications of these findings, for the taxonomy of granulocytic ehrlichiae and the potential for human infections to occur in the U.K., is discussed.
148 citations
TL;DR: A large number of the subjects studied had previously been diagnosed with Chagas y Leishmaniosis, a common tick-borne infection that can be fatal to animals and humans.
Abstract: J . P. D U J A R D I N ,1 , 2 M . M U Ñ O Z ,3 T . C H AV E Z , 3 C . P O N C E ,4 J . M O R E N O ,5 and C . J . S C H O F I E L D6 1UMR CNRS-ORSTOM 9926, BP 5045, Montpellier cedex 1, France, 2ORSTOM/IBBA, CP 9214, La Paz, Bolivia, 3Instituto Boliviano de Biologia de Altura, Calle Claudio Sanjinez, La Paz, Bolivia, 4Laboratorio de Referencia de Enfermedad de Chagas y Leishmaniosis, Ministerio de Salud Publica, Apartado 4695, Tegucigalpa, Honduras, 5Facultad de Ciencias Exactas y Naturales, Universidad de Antioquia, Medellin, Colombia and 6Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London WC1E 7HT, U.K.
105 citations
TL;DR: The genetic structure of T. infestans natural populations followed an ‘isolation by distance’ model, involving a series of founder effects followed by genetic drift, rather than adaptation in response to differential selection pressures, which conforms with circumstantial evidence that T.infestans spread, mainly in association with recent human migrations, from a source, probably in southern Bolivia.
Abstract: #Triatoma infestans$ (#Hemiptera$ : #Reduviidae$) from 22 Andean localities in Bolivia (n=968) and Peru (n=37) were analysed by multi-locus enzyme electrophoresis. Among 12 gene-enzyme systems analysed, GPD, 6GPD and PCM were polymorphic, ACON, G6PD, GPI, IDH, LAP, MDH, ME, PEP-A and PEP-B were monomorphic. Allozyme frequencies were analysed in relation to geographical and climatic factors, and the presence or absence of #Trypanosoma cruzi$ infection. At one locality (Vallegrande, Bolivia), the frequency of 6Pgd-1 was significantly higher in infected (41% of 85) than in uninfected (17% of 83) adult #T. infestans$, although no such difference was found among nymphs (n=347). From other localities, only insects infected with #T. cruzi$ were subjected to isosyme analysis. Populations of #T. infestans$ within villages showed panmixia, while genetic differenciation of #T. infestans$ between villages was correlated with the distance between them. The genetic structure of #T. infestans$ natural populations followed an "isolation by distance" model, involving a series of founder effects followed by genetic drift, rather than adaptation in response to differential selection pressures. This conforms with circumstantial evidence that #T. infestans$ spread, mainly in association with recent human migrations, from a source, probably in southern Bolivia. Isoenzyme characterization of populations of #T. infestans$ could be used to infer sources of re-infestation during the surveillance phase of control programs. (Resume d'auteur)
105 citations
TL;DR: The results suggested that C.’bolitinos populations are capable vectors of the BLU viruses in South Africa, and the C. v. sonorensis colonies had a significantly lower susceptibility to infection with BLU’1, 3 and 4 than C.
Abstract: The susceptibility of field-collected Culicoides bolitinos to infection by oral ingestion of bluetongue virus serotypes 1, 3 and 4 (BLU 1, 3 and 4) was compared with that of field-collected C. imicola and laboratory reared C. variipennis sonorensis. The concentration of the virus per millilitre of bloodmeal was 10(5.0) and 10(6.0)TCID50 for BLU 4 and 10(7.2)TCID50 for BLU 1 and 3. Of 4927 C. bolitinos and 9585 C. imicola fed, 386 and 287 individual midges survived 10 days extrinsic incubation, respectively. Midges were assayed for the presence of virus using a microtitration assay on BHK-21 cells and/or an antigen capture ELISA. Infection prevalences for the different serotypes as determined by virus isolation ranged from 22.7 to 82.0% in C. bolitinos and from 1.9 to 9.8% in C. imicola; infection prevalences were highest for BLU 1, and lowest for BLU 4 in both species. The mean log10 TCID50 titre of the three BLU viruses per single fly was higher in C. bolitinos than in C. imicola. The results suggested that C. bolitinos populations are capable vectors of the BLU viruses in South Africa. A high correlation was found between virus isolation and ELISA results for the detection of BLU 1, and less for BLU 4; the ELISA failed to detect the presence of BLU 3 in infected flies. The C. v. sonorensis colonies had a significantly lower susceptibility to infection with BLU 1, 3 and 4 than C. bolitinos and C. imicola. However, since infection prevalence of C. v. sonorensis was determined only by ELISA, this finding may merely reflect the insensitivity of this assay at low virus titres, compared to virus isolation.
99 citations
TL;DR: Mark–release–recapture experiments with Anopheles gambiae s.s.l. were performed during the wet seasons of 1993 and 1994 in Banambani, Mali, and observed no difference in dispersal between the two species, nor among the chromosomal forms of An.
Abstract: Mark–release–recapture experiments with Anopheles gambiae s.l. were performed during the wet seasons of 1993 and 1994 in Banambani, Mali. All recaptured mosquitoes were identified to species by PCR analysis and, when possible, by chromosomal analysis to chromosomal form. Two species of the An. gambiae complex were present: An. gambiae s.s. and An. arabiensis; their ratio differed greatly from one year to the next. Three chromosomal forms of An. gambiae s.s. were found – Bamako, Savanna and Mopti. The drier 1993 was characterized by a high frequency of An. arabiensis and of the Mopti chromosomal forms of An. gambiae s.s. These trends were consistent with large-scale geographical patterns of abundance along a precipitation gradient. We observed no difference in dispersal between the two species, nor among the chromosomal forms of An. gambiae s.s. Therefore, in this situation at least, it is reasonable to group such data on the An. gambiae complex as a whole for analysis. Population size of An. gambiae s.l. females in the village was estimated to be 9000–11 000 in 1993 and 28 000 in 1994. The corresponding numbers were somewhat higher when independently-derived values of daily survival were used. These were consistent with estimates of effective population size obtained from patterns of gene frequency change.
TL;DR: Catches of other mosquito species showed consistent differences between all treatments which appear to be associated with differences in host‐preference, suggesting that the importance of CO2 in host-seeking behaviour of mosquitoes increases with the degree of zoophily.
Abstract: Field studies on responses of two mosquito sibling species, Anopheles arabiensis Patton and An. quadriannulatus Theobald, to a man, a calf and different release rates of carbon dioxide (man, calf and cow equivalents) were conducted in north-eastern South Africa. Various combinations of baits were compared in two-choice tests, using two mosquito nets, placed 2.5 m apart and 10 cm off the ground. Mosquitoes attracted to the baits were able to enter the nets from below and were collected by means of a suction tube. In a two-choice test between a man and CO2 (human equivalent, 250 ml/min), 81% of the An. quadriannulatus were caught with CO2. The reverse was seen for An. arabiensis, where only 20% of the total catch was caught with CO2 compared to man. High release rates of CO2 (cow equivalent, 800 ml/min) attracted significantly more An. quadriannulatus than the low release rate (250 ml/min), whereas no significant effect of the release rate of CO2 on the total catch of An. arabiensis was seen. In the latter species, up to 33% of the attraction of human emanation is attributable to carbon dioxide. Anopheles quadriannulatus was equally attracted to a calf and CO2 (calf equivalent, 180 ml/min). Catches of other mosquito species showed consistent differences between all treatments which appear to be associated with differences in host-preference, suggesting that the importance of CO2 in host-seeking behaviour of mosquitoes increases with the degree of zoophily.
TL;DR: The shortest MDPBs were obtained in large cages with high densities of mosquitoes and longest protection times occurred in medium sized cages with low mosquito densities.
Abstract: Mosquito biting rates and the mean duration of protection (in hours) from bites (MDPB) of Aedes aegypti and Anopheles quadrimaculatus, using the repellent 'deet' (N,N-diethyl-3-methylbenzamide) on a 50 cm2 area of healthy human skin, were observed in small (27 l), medium (approximately 65 l) and large (125 l) cages containing low, medium or high densities of mosquitoes: respectively, 640, 128 or 49 cm3 of cage volume per female. At the initial treatment rate of approximately 0.4 microliter/cm2 (1 ml of 25% deet in ethanol on 650 cm2 of skin), the MDPB for deet against Ae. aegypti ranged from 4.5 to 6.5 h and was significantly less (5.0 +/- 0.8 h) in large cages compared with medium (6.2 +/- 0.9 h) and small (6.2 +/- 0.8 h) cages, regardless of the density. Against An. quadrimaculatus the MDPB for deet 0.4 microliter/cm2 was 1.5-8.0 h, less in small (3.7 +/- 2.3 h) and large (2.2 +/- 1.1 h) cages at medium (3.7 +/- 2.3 h) and high (2.5 +/- 1.7 h) mosquito densities, and was longest in medium cages (6.2 +/- 2.6 h) at low mosquito densities (5.8 +/- 2.8 h). With equinoxial photoperiodicity (light on 06.00-18.00 hours) the biting rate was influenced by the time of observation (08.00, 12.00, 16.00 hours) for Ae. aegypti but not for An. quadrimaculatus. For both species, the biting rate was inversely proportional to mosquito density and the MDPB. The shortest MDPBs were obtained in large cages with high densities of mosquitoes and longest protection times occurred in medium sized cages with low mosquito densities.
TL;DR: It is proposed that areas of Morocco with higher levels of soil moisture in late summer or autumn provide more, larger and/or more enduring breeding sites for C. imicola, as well as supporting more photosynthetically active vegetation and hence having higher NDVI.
Abstract: African horse sickness (AHS) is a vector-borne, infectious disease of equids caused by African horse sickness virus (AHSV). The only proven field vector of the virus is the biting midge Culicoides imicola. Following a recent epizootic (1989-91) of AHS in Morocco, light traps and automatic weather stations were operated for 2 years at twenty-two sites distributed over much of the country. The annually-averaged mean daily trap catch of C. imicola at these sites was negatively correlated with wind speed, and positively correlated with the average and mean annual minimum NDVI (Normalized Difference Vegetation Index, a remotely sensed measure of vegetation activity). There were no significant correlations between the mean daily trap catch and air temperature, soil temperature, relative humidity, saturation deficit, rainfall, altitude or the mean annual maximum or range of NDVI. The best two-variable model, which combined WindspeedMnAvMn (the average daily minimum wind speed of the least windy month) and NDVImin (the average annual minimum NDVI) as predictors, explained over 50% of the variance in the annually-averaged mean daily trap catch of C. imicola. There was a significant, positive correlation between minimum wind speed at night and the daily mortality rate of adult female C. imicola and it is suggested that the relationship between wind speed and the abundance of C. imicola arises from effects on adult mortality or dispersal. Considering several climatic variables, in North Africa NDVImin was most significantly correlated with total annual rainfall. It is suggested that the relationship between NDVImin and the abundance of C. imicola arises from the impact of soil moisture on both. It is proposed that areas of Morocco with higher levels of soil moisture in late summer or autumn provide more, larger and/or more enduring breeding sites for C. imicola, as well as supporting more photosynthetically active vegetation and hence having higher NDVI.
TL;DR: The distribution of Borrelia burgdorferi sensu lato, the Lyme borreliosis agent, was surveyed in British ticks in the collection of the Natural History Museum, London.
Abstract: The distribution of Borrelia burgdorferi sensu lato, the Lyme borreliosis agent, was surveyed in British ticks in the collection of the Natural History Museum, London. Alcohol-preserved specimens of eight species of ticks known to attack humans were studied: Ixodes ricinus, I. hexagonus, I. uriae, I. trianguliceps, Dermacentor reticulatus, Haemaphysalis punctata, Rhipicephalus sanguineus and Argas vespertilionis. The sample comprised all life stages and originated from a wide range of host species, collection dates (1896-1994) and geographical localities in England, Scotland and Wales. Borrelia burgdorferi s.l. DNA, detected by a polymerase chain reaction that targeted the outer surface protein A gene, was found in all eight species. The overall proportion of PCR-positive specimens ranged from 7.8% for I. hexagonus (mostly from mustelids and hedgehogs) to 98.3% for I. uriae (mostly from seabirds). Borrelia burgdorferi s.l. DNA was found for the first time in the bat parasite A. vespertilionis (85.3%). The spirochaete is newly recorded in British populations of I. trianguliceps (97.4%, mostly from voles, mice and shrews), D. reticulatus (12.5% from dog and man) and R. sanguineus (30% from dogs and human dwellings). Of the four tick species with larvae available for testing, examples of I. ricinus, I. uriae and A. vespertilionis were PCR positive, as were significantly more nymphs than adults of I. ricinus, I. hexagonus and A. vespertilionis. Analyses showed that B. burgdorferi s.l. has been consistently present in British tick populations since at least 1897. Ticks positive for B. burgdorferi s.l. DNA were collected in all months of the year, throughout Britain, and were found on a wide range of mammal and bird species. PCR positivity does not prove vector or reservoir competence, but the use of archived material has demonstrated an extensive range of host-tick relationships involving B. burgdorferi s.l. in Britain for > 100 years.
TL;DR: In this paper, the transmission of Trypanosoma evansi (South American origin) and T. congolense of Kilifi DNA type (Kenyan origin) was studied in laboratory mice using the African stable flies Stomoxys niger niger and S. niger.
Abstract: Mechanical transmission of Trypanosoma evansi (South American origin) and T. congolense of Kilifi DNA type (Kenyan origin) was studied in laboratory mice using the African stable flies Stomoxys niger niger and S. taeniatus. Altogether, 355 flies were interrupted after feeding on infected blood and then transferred immediately to an uninfected mouse to complete feeding. Microscopy and subinoculation of triturated flies into uninfected mice demonstrated the survival of T. congolense in Stomoxys for up to 210 min and T. evansi for up to 480 min. Parasites survived for much longer periods in the digestive tract than inside or on the mouthparts. Trypanosoma congolense was transmitted only by S. n. niger, and only at low rates of 3, 8 and 10% using flies of different feeding histories: fed on blood the previous day, freshly caught, and teneral. Trypanosoma evansi was transmitted by both Stomoxys species at higher rates: S. taeniatus range 13-18%; S. n. niger range 17-35%. The highest transmission rate occurred with the combination of teneral S. n. niger and T. evansi.
TL;DR: The results of tick surveys carried out in the Eastern province of Zambia between December 1982 and February 1996 were principally in agreement with the findings of earlier surveys conducted during the period 1965–72, but the main difference between the present survey and the previous one concerns the status of Rhipicephalus appendiculatus.
Abstract: The results of tick surveys carried out in the Eastern province of Zambia between December 1982 and February 1996 were principally in agreement with the findings of earlier surveys conducted during the period 1965-72. Boophilus decoloratus has almost been replaced by Boophilus microplus. Hyalomma truncatum was found in small numbers throughout the province and Hyalomma marginatum rufipes was only rarely encountered in collections made from cattle. Rhipicephalus evertsi evertsi was largely confined to the southern part of the plateau and the valleys of the Zambezi tributaries. The main difference between the present survey and the previous one concerns the status of Rhipicephalus appendiculatus. This species is currently expanding its range in a westward direction, whereas it was virtually absent from the southern part of the province during the period 1965-72. The majority of specimens collected are morphologically intermediate between R. appendiculatus and the closely allied Rhipicephalus zambeziensis. The available evidence indicates that R. zambeziensis (sensu stricto) is absent from the province. The phenology of R. appendiculatus is aberrant in the province: at lower altitudes a second generation of adult ticks is recorded on the hosts at the start of the dry season.
TL;DR: The main entomological justification for the current enthusiasm for the use of impregnated bednets for malaria control in Africa is that most biting by the vector mosquitoes happens at hours of the night when most people are in bed and under nets if they have them, but this should take into account the possibility that the dangerous older and malaria sporozoite-positive mosquitoes may bite earlier or later at night than the majority of younger mosquitoes.
Abstract: The main entomological justification for the current enthusiasm for the use of impregnated bednets for malaria control in Africa is that most biting by the vector mosquitoes (mainly Anopheles gambiaeGiles sensu latoand An. funestusGiles) happens at hours of the night when most people are in bed and under nets if they have them (Hamon, 1963; Snow et al., 1988). A more exact quantification of the likely impact of nets should take into account the possibility that the dangerous older (parous) and malaria sporozoite-positive mosquitoes may bite earlier or later at night than the majority of younger mosquitoes. Table 1 summarizes reports of such effects, the data being grouped into successive 4-h periods of the night. In East Africa, Gillies (1957) found a declining trend of sporozoite rate during the night, whereas Robert & Carnevale (1991) and Bockarie et al. (1996) for An. gambiaeand An. funestusin West Africa and Bockarie et al., (1996) for An. punctulatusin Papua New Guinea observed increasing parity and/or sporozoite rate during the night: significant in three cases out of five when we tested by χ2 for trend. A comparable study was carried out in the village of Mafere, near Muheza (5°12 9S, 38°499E), in northeastern Tanzania. The mosquitoes were collected by hourly emptying of the bags of three light traps, each set indoors for four nights beside an occupied, untreated bednet. This sampling method was used in preference to human landing catches, as this area has intense transmission of Plasmodium falciparummalaria showing resistance to pyrimethamine-sulfadoxine (Trigg et al., 1997) as well as to chloroquine. Previously in this area, in seasons of high and low mosquito density, light traps in three rooms were found to catch approximately as many mosquitoes as were collected by two human catchers in one room in the same village (Lines et al., 1991). Parous and sporozoite rates of anophelines caught in light traps agreed with those in comparable samples collected indoors by other methods.
TL;DR: Investigation of population densities of Lutzomyia gomezi and Lu.
Abstract: In north-central Venezuela Lutzomyia gomezi and Lu. ovallesi are the main endophilic/anthropophilic species of phlebotomine sandflies implicated as vectors of cutaneous leishmaniasis (CL). Lutzomyia ovallesi has been found infected with Leishmania braziliensis (1.2%) and less often with Le. mexicana (0.07%), while Le. braziliensis infections have also been found in Lu. gomezi (0.47%). We investigated population densities of these sandflies using two sampling methods with four series of collections between January 1991 and March 1995 at El Ingenio, Miranda State. All-night outdoor collections from a Shannon trap were correlated with indoor collections from CDC light-traps by linear regression, which proved to be statistically significant for both species. Estimated numbers of female sandflies per house per night were found to be proportional to monthly precipitation (i.e. rainfall), with a lag time of seven months for Lu. ovallesi and of six months for Lu. gomezi. Predominance of Lu. ovallesi over Lu. gomezi (c. 10:1) was observed throughout the year, with the number of infected females estimated as 0.043+/-0.047 Lu. ovallesi and 0.0085+/-0.0124 Lu. gomezi per CDC trap per house per night (ratio approximately 5:1). The mean rate of new CL cases per house per year and sandfly abundance were correlated by linear regression, showing a statistically significant relationship for Lu. ovallesi but not for Lu. gomezi. The negative intercept indicated that, on average, the CDC trap density exceeds 800 Lu. ovallesi females/house/year before new CL cases occur at El Ingenio.
TL;DR: The urban mosquitoAedes aegypti (L.) (Diptera: Culicidae) transmits dengue and yellow fever in many tropical countries and it has been suggested that elevated esterase activity may also be associated with insecticide resistance in Ae.
Abstract: The urban mosquitoAedes aegypti (L.) (Diptera: Culicidae) transmits dengue and yellow fever in many tropical countries. In Caribbean islands, Ae. aegyptiposes an increasing public health threat where dengue types 1, 2 and 4 are endemic (Nathan & Knudsen, 1991). Aedes aegypti control is undertaken through community participation in the elimination of watercontainer breeding-sites, with variable success. Organophosphorus insecticides (OPs) have also been used against Ae. aegyptiduring the last 15–20 years (Georghiou et al., 1987). In Trinidad, temephos 1% sand granules are routinely applied for larval control in water storage containers, while malathion is used as an adulticide by ultra low volume spraying during periods of high prevalence of mosquitoes and/or dengue. Resistance to a range of OPs has been detected at low levels in Trinidad populations of Ae. aegypti , affecting both the larval and adult life stages (Rawlins & Wan, 1995). OP resistance in strains of Culex mosquitoes is commonly mediated by two different mechanisms: (1) elevated esterase activity, due to the gene amplification and/or increased transcription (Raymond et al., 1989; Vaughan & Hemingway, 1995) and subsequent over-expression of nonspecific esterases (Prabhaker et al., 1987; Takahashi & Yasutomi, 1987; Hemingway et al., 1990; Wirth et al., 1990) which sequester the OP before it reaches its target site, acetylcholinesterase (AChE). (2) Insecticide-insensitive AChE (iAChE) (Kamimura & Maruyama, 1983; Raymond et al., 1985; Villani & Hemingway, 1987). It has been suggested that elevated esterase activity may also be associated with insecticide resistance inAe. aegypti(Mourya et al., 1993). However, to date, neither elevated esterase activity nor iAChE have actually been identified as insecticide resistance mechanisms in Ae. aegypti . In Culex mosquitoes, the
TL;DR: The distribution of these twelve cytological taxa was assessed in relation to the two main vegetation zones of West Africa, topography, river size and other factors, and the range of each species was influenced by seasonal climatic changes in wind movement and river water level.
Abstract: During the decade from 1984 to 1993, nine species of the Simulium damnosum complex of blackflies (Diptera: Simuliidae) were identified from the area covered by the Onchocerciasis Control Programme. These were S. damnosum s.s., S. dieguerense, S. konkourense, S. leonense, S. sanctipauli, S. sirbanum, S. soubrense, S. squamosum, and S. yahense. Some of these species were found to consist of two chromosomal variant populations. These were S. konkourense 'Konkoure' and 'Menankaya' forms, S. sanctipauli sensu stricto and 'Djodji' form, S. soubrense 'Chute Milo' and 'Beffa' forms. The distribution of these twelve cytological taxa was assessed in relation to the two main vegetation zones of West Africa (forest and savanna), topography, river size and other factors. The range of each species was influenced by seasonal climatic changes in wind movement and river water level. The most widely distributed species were S. sirbanum and S. damnosum s.s., associated with savanna areas, recorded from all river basins. Simulium dieguerense was restricted mainly to Western Mali on the Rivers Bafing and Bakoye in the Senegal River basin. Simulium squamosum was identified from rivers draining mountainous areas in both the forest and savanna zones. Simulium yahense was found in small permanent rivers along a wide forested band parallel to the coast and was absent from the plains of Togo and Benin. Members of the S. sanctipauli subcomplex had restricted distributions except for S. sanctipauli s.s., which was widespread in large rivers of the forest zone from Sierra Leone to the Volta Lake in Ghana. Simulium soubrense 'Beffa' form occurred in Togo and Benin, S. soubrense 'Chutes Milo' form in Guinea, both 'Konkoure' and 'Menankaya' forms of S. konkourense occurred predominantly in Guinea and S. leonense in Sierra Leone. The relevance of the distribution maps and the importance of the data bank to vector control larvicidal operations are discussed.
TL;DR: In Zimbabwe, studies were made of the landing and feeding responses of Glossina pallidipes on an ox, finding that the probability of feeding was not significantly affected by age as determined by ovarian category but there was a paucity of young flies attracted to the ox.
Abstract: In Zimbabwe, studies were made of the landing and feeding responses of Glossina pallidipes on an ox. Of the tsetse approaching an ox, approximately 70% fed. Increasing densities of tsetse increased the grooming responses of the ox but had no significant effect on the percentage of tsetse that engorged. The landing site of tsetse on the ox varied with density, with approximately 50% landing on the legs at low densities ( 40 flies per ox. For male G. pallidipes, the mean bloodmeal size was 37 mg. The probability of feeding was negatively correlated with fat content, declining from 91% for flies with 4 mg fat. Bloodmeal size was also negatively correlated with fat content; the regression equation relating bloodmeal size and fat content indicated that the mean wet weight declined from 42 mg for flies with 1 mg of fat to 31 mg for flies with 5 mg of fat. For females, the probability of feeding was not significantly affected by age as determined by ovarian category but there was a paucity of young (ovarian category 0) flies attracted to the ox. Pregnancy status had no significant effect on the probability of feeding, but samples of flies attracted to the ox showed a relative dearth of females approaching larviposition and a preponderance just after.
TL;DR: Bioassays using a laboratory strain of Aedes aegypti demonstrated that thanaka is itself slightly repellent at high dosages and the mixture with deet provides protection for over 10 h, which would also provide some personal protection against dengue, which is increasing locally.
Abstract: The prevention and treatment of drug-resistant malaria is becoming increasingly difficult. On the Thai–Myanmar border multi-drug resistant strains of falciparum malaria are increasing and, because the malaria vector Anopheles bite outdoors during early evening, insecticide house-spraying or impregnated bednets provide only limited protection. Therefore, the protective efficacy of repellent formulations containing di-methyl benzamide (deet) and permethrin against local vectors was estimated, when applied to the skin, and their acceptability amongst pregnant Karen women who are at relatively high risk from malaria was assessed. Human landing catches of mosquitoes showed that almost complete protection was achieved using different formulations of 20% deet and 0.5% permethrin for up to 6 h. All-night collections from human subjects indicated that this repellent combination reduced exposure to malaria parasites by at least 65 and 85% for those transmitted by Anopheles minimus and An. maculatus, respectively, the two principal vectors in this area. Pregnant women in the camps preferred repellents which were mixed with ‘thanaka’, a root paste made from pulp of the wood apple tree, Limonia acidissima, used locally as a cosmetic. Apart from a temporary warming sensation where repellent thanaka was applied to the skin, the repellents were well tolerated. An intervention trial is currently in progress to determine whether deet mixed with thanaka can protect pregnant women against malaria in this part of the world. Bioassays using a laboratory strain of Aedes aegypti demonstrated that thanaka is itself slightly repellent at high dosages and the mixture with deet provides protection for over 10 h. This treatment would therefore also provide some personal protection against dengue, which is increasing locally, transmitted by Ae. aegypti and Ae. albopictus biting during the daytime.
TL;DR: A collagen membrane technique, based on the membrane blood‐feeding system of Cosgrove et al. (1994) , was used to compare repellents against Aedes aegypti mosquitoes.
Abstract: A collagen membrane technique, based on the membrane blood-feeding system of Cosgrove et al. (1994) , was used to compare repellents against Aedes aegypti mosquitoes. Repellency was defined in terms of inhibition of probing (ED50 and ED90) after 5 min exposure. A direct comparison was made with repellency from probing after 5 min on five male volunteers.
Four repellent products were compared with technical DEET as the standard. The liquid formulations tested were: Autan® (20% deet; Bayer); Repel Plus® (20% deet plus 0.05% permethrin; Boots); permethrin (Zeneca) and citronellal (Sigma) .
Membrane and arm tests gave similar results. Deet formulations required less active compound than citronellal for the same degree of repellency. Pure deet and Autan gave similar results, dose for dose. Permethrin was highly repellent at very low doses, but Repel Plus did not enhance the immediate repellency of deet. A technique using the same membrane system was developed to evaluate persistence of Autan, which declined to 75% after 1 h against Ae. aegypti, and to about 50% after 2–4 h.
TL;DR: During the years 1993–1995, a total of 3580 culicine mosquitoes of six species were collected in South Moravia, Czech Republic, and examined by dark‐field microscopy for the presence of borreliae, finding one isolate from Ae.
Abstract: During the years 1993-1995, a total of 3580 culicine mosquitoes of six species were collected in South Moravia, Czech Republic, and examined by dark-field microscopy for the presence of borreliae. Females of Aedes cantans, Ae. sticticus, Ae. vexans, Culex pipiens and Cx pipiens biotype molestus (but not Ae. geniculatus or Culiseta annulata) harboured spirochaetes, the frequencies ranging from 0.7% to 7.8%. One isolate (BR-53) from Ae. vexans was identified as Borrelia afzelii genospecies. The potential role of mosquitoes in the epidemiology of Lyme borreliosis should be investigated.
TL;DR: This method is inexpensive, simple, rapid to perform and suitable for use in developing countries to identify and distinguish different serotypes of dengue virus in their vectors during eco‐epidemiological investigations.
Abstract: Adult Aedes aegypti mosquitoes were collected in Puerto Triunfo, central Colombia, where dengue is endemic, during a six month period. Viral infection within the head of each individual mosquito was identified by an immunofluorescent assay (IFA) using a flavivirus-specific monoclonal antibody. The dengue virus serotype, present in each flavivirus-positive specimen, was then determined in portions of the remaining thorax using IFAs with serotype-specific monoclonal antibodies. Among 2065 female Aedes aegypti collected and tested, twenty-four flavivirus-positive individuals were found (minimum infection rate 11.6%), three identified as dengue type-1 and twenty-one as dengue type-2 virus. This was consistent with the isolation of only these two serotypes of dengue virus from dengue fever patients within this town. No vertical transmission of dengue virus could be detected in 1552 male Aedes aegypti collected. This method is inexpensive, simple, rapid to perform and suitable for use in developing countries to identify and distinguish different serotypes of dengue virus in their vectors during eco-epidemiological investigations.
TL;DR: The feasibility of using electric nets, baited with human breath or carbon dioxide, for sampling mosquitoes in Tanzania is studied to develop odour-baited traps for the African malaria vectors of the An.
Abstract: Electric nets were developed by Vale (1974) for sampling tsetse flies (Diptera: Glossinidae). They have been used to investigate tsetse responses to host odours and synthetic kairomones (Vale & Hall, 1985), to analyse fly behaviour around hosts and in odour plumes (Torr, 1988), to estimate the proportions of flies feeding on hosts (Vale, 1977) and to test the sampling efficiencies of numerous trap and target designs (e.g. Vale & Hargrove, 1979). Gillies et al. (1978) adopted Vale’s technology to study flight behaviour of mosquitoes (Diptera: Culicidae) in relation to prevailing wind directions and the influence of wind on the flight speed of West African mosquitoes (Gillies & Wilkes, 1981). They modified the electric net design by reducing the distance between wires from 8 mm for tsetse (Vale, 1974) to 5 mm for mosquitoes, charged with a lower voltage output (2 kV). The potential of using electric nets for sampling mosquitoes was clearly demonstrated, but they have never been used to study responses to odour baits and to analyse flight behaviour in odour plumes. We are currently in the process of screening human odours for behavioural activity in the laboratory (Knols et al., 1994, 1997) in order to develop odour-baited traps for the African malaria vectors of theAn. gambiaeGiles complex. Evaluation of candidate odours under field conditions depends heavily on the availability of sampling devices which can be used outdoors. We therefore studied the feasibility of using electric nets, baited with human breath or carbon dioxide, for sampling mosquitoes in Tanzania; see Charlwood et al. (1995) for a description of the area. Three types of electric nets (‘small’, ‘large’ and ‘cylindrical’) were used in the experiments. Small nets (15 3 17 cm, Fig. 1A) consisted of a grid of seventy stainless steel wires (diameter 0.2 mm), attached to Fabory ® zinc-plated draw springs (0.53 3.53 20 mm) on one side (conductors) and nylon
TL;DR: Bednets treated with alphacypermethrin are well accepted, effectively killed anopheline mosquitoes and should therefore be evaluated for personal protection against malaria transmission.
Abstract: . In the Gambian village of Saruja, where malaria is transmitted mainly by mosquitoes of the Anopheles gambiae complex, a trial was undertaken of the acceptability and efficacy of bednets treated with one of three pyrethroid insecticides – alphacypermethrin 40 mg/m 2 , permethrin 500 mg/m 2 and lambdacyhalothrin 10 mg/m 2 . Fewer mosquitoes were found alive under nets treated with insecticide than under control nets. Significantly more dead mosquitoes were found under nets treated with alphacypermethrin than under nets treated with permethrin or lambdacyhalothrin. Side-effects were reported by a proportion of the users of nets treated with each of the insecticides, but none were severe and their prevalence was similar between treatment groups. Unwashed nets treated with alphacypermethrin were more effective at killing anopheline mosquitoes in bioassays than nets treated with permethrin or lambdayhalothrin. Killing activity was reduced when nets were washed, irrespective of which insecticide was used. Bednets treated with alphacypermethrin are well accepted, effectively killed anopheline mosquitoes and should therefore be evaluated for personal protection against malaria transmission.
TL;DR: Analysis of the efficacy of tags impregnated with pheromone and acaricide for control of Amblyomma variegatum on cattle in Guadeloupe indicated that, within 2 days of placement, cyfluthrin spread rapidly over the body from the tags.
Abstract: The efficacy of tags impregnated with pheromone and acaricide for control of #Amblyomma variegatum# on cattle in Guadeloupe was determined for a 13-week trial. Comparisons were made between untreated cattle and cattle with tags containing either pheromones alone (o-nitrophenol, methyl salicylate, 2,6-dichlorophenol and phenylacetaldehyde), pheromones plus acaricide (cyfluthrin or deltamethrin), or acaricide alone. Tags were fastened to cattle both on collars on the neck and with adhesive to tail hairs, with over 98 and 90% of tags retained, respectively, during the trial. By the end of the trial, tick infestations increased on untreated cattle (311.7%) and cattle with pheromone tags (154.8%) but decreased on cattle with pheromone/cyfluthrin (-45.0%), cyfluthrin (-42.8%), pheromone/deltamethrin (-68.7%) and deltamethrin tags (-87.6%). Cattle with pheromone tags had greater proportions of ticks on the hind regions (81%) compared to untreated cattle (62.5%) and on the front regions (18.2%) compared to untreated cattle (8.2%) indicating that ticks aggregated in response to pheromones. Analysis of hair samples by gas chromatography indicated that, within 2 days of placement, cyfluthrin spread rapidly over the body from the tags. Both cyfluthrin and deltamethrin were present in detectable levels on all eight body regions examined throughout the trial. Analysis of the tags indicated that they all still contained pheromone components after 13 weeks under field conditions. (Resume d'auteur)
TL;DR: For two strains of L. major (LV 561 and Neal‐P), galactosamine substantially enhanced the establishment of infection in the sandfly posterior midgut and significantly increased parasite loads after defaecation, but did not affect anterior migration of Leishmania.
Abstract: Galactosamine, which has been shown in vitro to specifically inhibit sandfly midgut lectin activity, was fed to Phlebotomus duboscqi females with blood containing promastigotes of Leishmania major. Non-inhibitory sugar, galactose, was added in controls. For two strains of L. major (LV 561 and Neal-P), galactosamine substantially enhanced the establishment of infection in the sandfly posterior midgut and significantly increased parasite loads after defaecation, but did not affect anterior migration of Leishmania. On day 3 post-infection, most infections in galactosamine-fed sandfly groups (92% of LV 561 and 100% of Neal-P) were found in the ectoperitrophic space of the posterior midgut, whereas most infections in the galactose-fed groups of sandflies (85% in LV 561 and 96% in Neal-P) were restricted to the peritrophic sac. On day 9, however, the proportion of infections colonizing the stomodeal valve was similar in both dietary groups of sandflies for both strains of L. major. The addition of galactosamine prevented the decrease of parasite loads which occurred in controls between days 3 and 6 post-infection. On days 6 and 9, heavy infections were observed almost exclusively in galactosamine-fed females. Differences between groups were more pronounced for the Neal-P strain, which normally developed poorly in sandflies. Morphology of L. major LV 561 was not affected by galactosamine supplement: the lengths of parasite body and flagellum were similar in both sandfly groups. Two hypotheses are considered for the role of sandfly midgut lectin in Leishmania development in the vector midgut. One proposes that sandfly lectin kills Leishmania promastigotes, the other assumes that lectin blocks LPG-mediated binding of promastigotes to sandfly midgut microvilli.