A large focus of naturally acquired Plasmodium knowlesi infections in human beings

Part 1 The importance of blood-sucking insects. Part 2 The evolution of the blood-sucking habit: prolonged close association with vertebrates morphological pre-adaptation for piercing. Part 3 Feeding preferences of blood-sucking insects: host choice host choice and species complexes. Part 4 Location of the host: the behavioural framework of host location appetitive searching activation and orientation attraction movement between hosts. Part 5 Ingestion of the blood meal: vertebrate haemostasis insect anti-haemostatic factors probing stimulants phagostimulants mouthparts blood intake. Part 6 Managing the blood meal: midgut anatomy the blood meal gonotrophic concordance nutrition host hormones in the blood meal partitioning of resources from the blood meal autogeny. Part 7 Host - insect interactions: insect distribution on the surface of the host morphological specializations for life on the host host immune responses to insect salivary secretions behavioural defences of the host density dependent effects on feeding success. Part 8 Transmission of parasites by blood-sucking insects: transmission routes specificity in vector-parasite relationships origin of vector parasite relationships.

Biology of Blood-Sucking Insects

BACKGROUND: Primary malaria prevention on a large scale depends on two vector control interventions: indoor residual spraying (IRS) and insecticide-treated mosquito nets (ITNs). Historically, IRS has reduced malaria transmission in many settings in the world, but the health effects of IRS have never been properly quantified. This is important, and will help compare IRS with other vector control interventions. OBJECTIVES: To quantify the impact of IRS alone, and to compare the relative impacts of IRS and ITNs, on key malariological parameters. SEARCH STRATEGY: We searched the Cochrane Infectious Diseases Group Specialized Register (September 2009), CENTRAL (The Cochrane Library 2009, Issue 3), MEDLINE (1966 to September 2009), EMBASE (1974 to September 2009), LILACS (1982 to September 2009), mRCT (September 2009), reference lists, and conference abstracts. We also contacted researchers in the field, organizations, and manufacturers of insecticides (June 2007). SELECTION CRITERIA: Cluster randomized controlled trials (RCTs), controlled before-and-after studies (CBA) and interrupted time series (ITS) of IRS compared to no IRS or ITNs. Studies examining the impact of IRS on special groups not representative of the general population, or using insecticides and dosages not recommended by the World Health Organization (WHO) were excluded. DATA COLLECTION AND ANALYSIS: Two authors independently reviewed trials for inclusion. Two authors extracted data, assessed risk of bias and analysed the data. Where possible, we adjusted confidence intervals (CIs) for clustering. Studies were grouped into those comparing IRS with no IRS, and IRS compared with ITNs, and then stratified by malaria endemicity. MAIN RESULTS: IRS versus no IRSStable malaria (entomological inoculation rate (EIR) 1): Two studies; for incidence and prevalence, the malaria rates were higher in the IRS group compared to the ITN group in one study. Malaria incidence was higher in the IRS arm in India (risk ratio IRS:ITN = 1.48) and in South Africa (risk ratio 1.34 but the cluster unadjusted CIs included 1). For malaria prevalence, ITNs appeared to give better protection against any infection compared to IRS in India (risk ratio IRS:ITN = 1.70) and also for both P. falciparum (risk ratio IRS:ITN = 1.78) and P. vivax (risk ratio IRS:ITN = 1.37). AUTHORS' CONCLUSIONS: Historical and programme documentation has clearly established the impact of IRS. However, the number of high-quality trials are too few to quantify the size of effect in different transmission settings. The evidence from randomized comparisons of IRS versus no IRS confirms that IRS reduces malaria incidence in unstable malaria settings, but randomized trial data from stable malaria settings is very limited. Some limited data suggest that ITN give better protection than IRS in unstable areas, but more trials are needed to compare the effects of ITNs with IRS, as well as to quantify their combined effects

Indoor residual spraying for preventing malaria

The precise function of eosinophils in parasitic infection in vivo remains poorly understood despite eosinophils having been shown to be potent effectors in killing parasites in vitro. Although it has long been held that the primary function of the eosinophil is protection against helminth parasites, there are little data to prove this unequivocally. Moreover, eosinophils are responsible for a considerable amount of inflammatory pathology accompanying helminth infections. This article will provide an overview of our current knowledge about eosinophils and their role, both protective and pathogenetic, in parasitic helminth infections.

The role of eosinophils in host defense against helminth parasites

Haemosporida is a large group of vector-borne intracellular parasites that infect amphibians, reptiles, birds, and mammals. This group includes the different malaria parasites (Plasmodium spp.) that infect humans around the world. Our knowledge on the full life cycle of these parasites is most complete for those parasites that infect humans and, to some extent, birds. However, our current knowledge on haemosporidian life cycles is characterized by a paucity of information concerning the vector species responsible for their transmission among vertebrates. Moreover, our taxonomic and systematic knowledge of haemosporidians is far from complete, in particular because of insufficient sampling in wild vertebrates and in tropical regions. Detailed experimental studies to identify avian haemosporidian vectors are uncommon, with only a few published during the last 25 years. As such, little knowledge has accumulated on haemosporidian life cycles during the last three decades, hindering progress in ecology, evolution, and systematic studies of these avian parasites. Nonetheless, recently developed molecular tools have facilitated advances in haemosporidian research. DNA can now be extracted from vectors' blood meals and the vertebrate host identified; if the blood meal is infected by haemosporidians, the parasite's genetic lineage can also be identified. While this molecular tool should help to identify putative vector species, detailed experimental studies on vector competence are still needed. Furthermore, molecular tools have helped to refine our knowledge on Haemosporida taxonomy and systematics. Herein we review studies conducted on Diptera vectors transmitting avian haemosporidians from the late 1800s to the present. We also review work on Haemosporida taxonomy and systematics since the first application of molecular techniques and provide recommendations and suggest future research directions. Because human encroachment on natural environments brings human populations into contact with novel parasite sources, we stress that the best way to avoid emergent and reemergent diseases is through a program encompassing ecological restoration, environmental education, and enhanced understanding of the value of ecosystem services.

Diptera vectors of avian Haemosporidian parasites: untangling parasite life cycles and their taxonomy

(1957). Studies on Filariasis in Malaya: Notes on the Breeding of Mansonia (Mansonioides) Mosquitoes in the Laboratory. Annals of Tropical Medicine & Parasitology: Vol. 51, No. 3, pp. 297-300.

Studies on filariasis in Malaya: notes on the breeding of Mansonia (Mansonioides) mosquitoes in the laboratory.

Although mosquitos of the Anopheles umbrosus group have long been recognized as important vectors of human malaria in Malaya, there have been doubts about the origin of some of the malaria infections found, especially in A. umbrosus and A. letifer. Investigations have accordingly been carried out in the Malayan swamp-forest, in conjunction with laboratory studies, into the nature of malaria infections in wild-caught mosquitos, the biting behaviour of anophelines and the presence of malaria infection in man and animals. The authors conclude from the results reported in this paper that A. umbrosus is a vector of mouse deer malaria and rarely, if ever, transmits primate malaria; that A. letifer transmits both human and mouse deer malaria; and that A. baezai and A. roperi are probably vectors of mouse deer malaria.

Investigations leading to the identification of members of the anopheles umbrosus group as the probable vectors of mouse deer malaria.

Investigations were conducted into the activity cycles of adult ♀ ♀ of Anopheles maculatus, A. letifer and A. campestris, which are known vectors of malaria in Malaya, and also 3 suspected vectors, A. umbrosus, A. roperi, and A. donaldi . They were designed to compare the results of biting catches on human baits made simultaneously both inside and outside houses, catches in human-baited net-traps, and pyrethrum knockdown collections made in houses during daytime. Because it was known that the forest species umbrosus, letifer, roperi and donaldi were active to some extent in the shade of the forest at all hours of the day, comparable catches were also carried out in the forest for continuous periods of 24 hrs.

Comparison of the indoor and outdoor biting catches show that both letifer and maculatus, and to a lesser extent donaldi, arc essentially exophagic, while campestris is endophagic. The biting catches also demonstrate that the species investigated have well-defined rhythms of activity. Pyrethrum sprays confirm that of these species only campestris rests regularly in the houses during the day.

Of the swamp-forest species, letifer and donaldi readily entered settlements during the night, but whilst the biting activity of letifer was similar in both the forest and the settlement, donaldi showed an active migration from the forest into the settlement during the night. A. roperi was never found outside the forest fringe, and umbrosus only rarely. The 24-hour biting catch in the forest showed that roperi has a remarkable peak of biting in the hour before dusk, when more than 50% of the day's biting occurred.

Net traps and biting catches measure different phenomena; net-traps the flight activity or entry into the settlements in the evening, biting catches the actual feeding activity of the species. Both techniques can be used for estimating population densities, but biting catches are more laborious and produce smaller numbers of mosquitos. The net-trap is undoubtedly more efficient for collection of mosquitos for dissection purposes. A sudden onset of activity in the net-traps soon after dusk suggests that when used for estimating densities it is imperative that trapping periods are related to sunset.

Mosquitos were dissected to reveal the age-compositions of the various populations caught by the different methods. Analysis failed to show any significant differences between the groups. However, it was statistically shown that there wasa tendency for a higher proportion of nulliparous maculates to bite during the first 3 hrs of the evening. A similar situation could not be demonstrated with the other species.

R. H. Wharton

Papers

Studies on filariasis in Malaya: notes on the breeding of Mansonia (Mansonioides) mosquitoes in the laboratory.

Investigations leading to the identification of members of the anopheles umbrosus group as the probable vectors of mouse deer malaria.

Studies on malayan vectors of malaria; methods of trapping, and observations on biting cycles.

Studies on filariasis in malaya: the effect of residual insecticides on Mansonia (Mansonioides) longipalpis.

An experiment in the control of rural malaria in Malaya.