Showing papers in "American Journal of Tropical Medicine and Hygiene in 1987"

Effect of temperature on the vector efficiency of Aedes aegypti for dengue 2 virus.

Abstract: The effect of temperature on the ability of Aedes aegypti to transmit dengue (DEN) 2 virus to rhesus monkeys was assessed as a possible explanation for the seasonal variation in the incidence of dengue hemorrhagic fever in Bangkok, Thailand. In two laboratory experiments, a Bangkok strain of Ae. aegypti was allowed to feed upon viremic monkeys infected with DEN-2 virus. Blood-engorged mosquitoes were separated into two groups and retained at constant temperatures. Virus infection and transmission rates were determined for Ae. aegypti at intervals ranging from 4 to 7 days during a 25-day incubation period. Results of the first experiment for mosquitoes infected with a low dose of DEN-2 virus and maintained at 20,24,26, and 3O"C, indicated that the infection rate ranged from 25% to 75% depending on the incubation period. However, DEN-2 virus was transmitted to monkeys only by Ae. aegypti retained at 30°C for 25 days. In the second experiment, the infection rate for Ae. aegypti that ingested a higher viral dose, and incubated at 26, 30, 32, and 35°C ranged from 67% to 95%. DEN-2 virus was transmitted to monkeys only by mosquitoes maintained at L 30°C. The extrinsic incubation period was 12 days for mos- quitoes at 3O"C, and was reduced to 7 days for mosquitoes incubated at 32°C and 35°C. These results imply that temperature-induced variations in the vector efficiency of Ae. aegypti may be a significant determinant in the annual cyclic pattern of dengue hemorrhagic fever epidemics in-Bangkok.

A ribosomal RNA gene probe differentiates member species of the Anopheles gambiae complex.

Abstract: A 0.59 kilobase DNA fragment cloned from an rDNA cistron of the mosquito Anopheles gambiae can be used as a probe to differentiate between A. gambiae, A. arabiensis, and A. melas, three morphologically identical sibling species in the A. gambiae complex which otherwise can be reliably distinguished only by polytene chromosome banding patterns. Although all are important (and often sympatric) African malaria vectors, their relative roles in malaria transmission have thus far been difficult to assess. The probe, an EcoRI-SalI fragment from the 3' end of the 28S beta coding region of the cistron, is present in all three species, but the species differ uniquely with respect to the location of an EcoRI site in the nontranscribed spacer (NTS) downstream of the fragment. We have routinely used the probe to identify A. gambiae complex mosquitoes to species on the basis of genomic DNA extracted from individual air dried specimens. A single mosquito abdomen provides more than sufficient DNA for the assay, and neither eggs nor a bloodmeal in the abdomen interfere with DNA yield. Moreover, the DNA extraction procedure does not degrade the bloodmeal IgG, so the residual protein pellet can be used to identify the mosquito bloodmeal source. Since the rDNA cistron organization as detected by the probe does not differ between male and female mosquitoes, the probe can be used for either sex. Preliminary experiments show that the probe is equally useful for mosquito larvae and pupae.

Reservoir competence of white-footed mice for Lyme disease spirochetes.

Abstract: Using the vector tick, Ixodes dammini, we described the reservoir competence of the white-footed mouse, Peromyscus leucopus, for the Lyme disease spirochete, Borrelia burgdorferi. Nymphal I. dammini were used to infect mammals, and larval ticks were used to diagnose infection (a form of xenodiagnosis). One tick was nearly as efficient as more than 1 in transmitting the spirochete to mice. The duration of the prepatent period was about 1 week. Prevalence of infection approached 100% in ticks that fed as larvae on mice infected 2 or 3 weeks previously. Thereafter, infectivity gradually decreased, but duration exceeded 200 days. Hamsters, too, became infectious for larval I. dammini. This report formally demonstrates the life cycle of B. burgdorferi as it seems to occur in nature. We conclude that the white-footed mouse is a competent reservoir for the Lyme disease spirochete.

Epidemiologic and clinical features of Crimean-Congo hemorrhagic fever in southern Africa.

Abstract: Following the diagnosis in 1981 of the first case of Crimean-Congo hemorrhagic fever (CCHF) in South Africa, an antibody survey was undertaken on cattle sera to determine the distribution of the virus and specific diagnostic tests were routinely applied to specimens from suspected cases of hemorrhagic fever to establish the medical significance of its presence. Antibody to CCHF virus was demonstrated by reversed passive hemagglutination-inhibition technique in 2,460/8,667 (28%) cattle sera and in 140/180 herds tested in South Africa, as well as in 347/763 (45%) cattle sera and in 32/34 (94%) herds tested in Zimbabwe. The antibody was found in all major cattle farming areas, but was of low prevalence along the southern coast where 2 of the 3 species of Hyalomma tick which occur in South Africa are absent. From February 1981 to January 1986, inclusive, 29 indigenous cases of CCHF were diagnosed in 16 outbreaks which arose in various locations throughout South Africa. A further 2 imported cases of CCHF arose in Zaire and Tanzania. The clinical features of infection conformed to the classical descriptions of CCHF in the Soviet Union. The fatal outcome in 11/31 cases indicates that the African disease is no less severe than that which occurs in Eurasia. It is inferred that the virus is widespread in all countries in Africa and Eurasia which lie within the limits of world distribution of ticks of the genus Hyalomma.

Diagnosis of Cutaneous and Mucocutaneous Leishmaniasis in Colombia: A Comparison of Seven Methods

Abstract: Seven methods of diagnosing leishmaniasis were compared in 177 patients presenting with lesions of the skin (165) or mucosa (12) in Tumaco and Cali, Colombia. The three methods of visualizing amastigotes in tissue samples (histological staining of tissue sections, impression smears of punch biopsies, and smears of dermal scraping from slits in the lesion margins) were less sensitive than the four Leishmania isolation methods (aspiration of lesion border cultured in biphasic media, aspirate inoculated into hamster nasal tissue, culture of punch biopsy macerate, and hamster inoculation of macerate). The aspirate-culture and biopsy-hamster methods employed in this study proved most sensitive of the four methods for the recovery of parasites. The combined overall sensitivity of the 7 methods was 67% for all enrolled patients and 75% for Montenegro skin test-positive patients. The individual sensitivities for the methods for all patients and Montenegro-positive positive, patients, respectively, were: histopathology 14% and 16%, impression smear 19% and 21%, dermal scraping 22% and 26%, aspirate-culture 58% and 64%, aspirate-hamster 38% and 41%, biopsy-culture 50% and 55%, and biopsy-hamster 52% and 57%. All methods were less sensitive in lesions of greater than 6 months duration than in lesions of more recent onset. Mucosal lesions were best diagnosed by the culture or hamster inoculation of a macerated mucosal biopsy. The diagnosis by inoculation of hamsters was achieved within 2 to 12 weeks, a mean of 34.5 days. Promastigotes were seen on Senekjie's medium within 3-8 days.(ABSTRACT TRUNCATED AT 250 WORDS)

Detecting artificial anti-dengue IgM immune complexes using an enzyme-linked immunosorbent assay.

Abstract: A variety of methods have been employed to detect viral immune complexes (IC) in clinical specimens. However, most techniques used were not antigen-specific. We developed a simple, specific double antibody sandwich technique to detect artificial anti-dengue (DEN) IgM immune complex (IgM-IC). Positive reactivity with IgM-ICs prepared with live DEN-1, -2, and -3 viruses was found to be related to IgM titers exceeding 1:20 and to the titer of the viruses. Most IgM-ICs prepared with live DEN-4 virus did not react. In contrast, IgM-ICs prepared with hemagglutination antigens, representing all 4 serotypes, reacted positively with amounts of antigens ranging from 2 to 8 units. These IgM-ICs were not type-specific.

Identification and distribution of New World Leishmania species characterized by serodeme analysis using monoclonal antibodies.

Abstract: Five hundred thirty stocks of Leishmania isolated from human and domestic and wild reservoir hosts, representing a wide geographic distribution of endemic foci of American cutaneous (ACL) and visceral leishmaniases (AVL) were characterized and identified at species and/or subspecies levels based on their reactivity to a cross-panel of specific monoclonal antibodies using a radioimmune binding assay. This study confirms and extends our preliminary results on the high specificity of some of these monoclonals for the L. braziliensis, L. mexicana, and L. donovani complexes. This study also demonstrates the relative stability of these molecular markers and the general usefulness of the method for parasite identification. Two hundred ninety-two of 420 isolates of ACL were classified as members of the L. braziliensis complex. Two hundred twenty-seven were L. b. braziliensis; these showed the widest geographical distribution (Brazil: Amazonas, Bahia, Ceara, Espirito Santo, Goias, Minas Gerais, Para, Paraiba, Rio de Janeiro, and Sao Paulo; Honduras: Santa Barbara and Yoko; Peru: Ancash, Piura, and Ucayali; and Venezuela: Cojedes, Distrito Federal, Lara, Portuguesa, Vale Hondo, Yaracuy, and Zulia). Forty-one stocks were identified as L. b. guyanensis (from North Brazil: Amazonas, Amapa, Para, and Rondonia). Twenty-one stocks were identified as L. b. panamensis (from Costa Rica: Alajuela, Guanacasten, Limon, Puntarenas, and San Jose; and Honduras: El Paraiso, and Olancho). Out of 128 isolates classified as members of the L. mexicana complex, 74 were differentiated as L. m. amazonensis (from Bolivia; Brazil: Amazonas, Bahia, Ceara, Goias, Maranhao, Mato Grosso do Norte, and Para; Peru: Pasco Forest and Van Humboldt; and Venezuela: Carabobo, Guarico, and Merida). Forty-four stocks were identified as L. m. venezuelensis (from Venezuela: Lara). Six stocks were L. m. mexicana (from Belize; and Mexico: Campeche [corrected] and Quintana Roo, Yucatan). One hundred ten isolates from AVL were identified as L. donovani chagasi (from Brazil: Bahia, Ceara, Maranhao, Minas Gerais, Mato Grosso do Sul, Piaui, Rio de Janeiro, and Sergipe; and Honduras: Valle). The implications of these results with respect to both the clinical and epidemiological data (including the detection of seven unusual characterized stocks) are discussed.

Monoclonal Antibodies Against Dengue 2 Virus E-Glycoprotein Protect Mice Against Lethal Dengue Infection,

Abstract: : A panel of 11 murine monoclonal antibodies directed against dengue type 2 was evaluated for antigen specificity by dot immunobinding assay and Western blot analysis and for in vitro and in vivo biological activities. Nine of the 11 monoclonal antibodies reacted with viral E-glycoprotein based on the Western blot analysis; one reacted with a 36 Kd protein present in dengue- infected C6/36 mosquito cells. The nine E-glycoprotein-reactive monoclonal antibodies also neutralized dengue 2 virus in a plaque reduction assay. Of the neutralizing monoclonal antibodies, five passivelly protected mice in vivo against lethal intracerebral dengue 2 challenge. The protective monoclonal antibodies were directed against viral determinants that fell into at least three spatialy separate families of epitopes on E-glycoprotein, the antigenicities of which were preserved after heat/detergent denaturation. Reprints.

Purification of Cryptosporidium Oocysts and Sporozoites by Cesium Chloride and Percoll Gradients

Abstract: The lack of an adequate system for the in vitro cultivation of Cryptosporidium spp. has forced researchers to work on infected feces or tissues. Molecular and immunological analyses of Cryptosporidium stages must be preceded by complex preparatory steps involving the concentration, storage, purification, excystation of oocysts, and purification of sporozoites. This paper describes two new procedures for the purification of Cryptosporidium. The first, consisting of pretreatment of oocysts with sodium hypochlorite followed by concentration using a Percoll gradient, is suitable for nucleic acid analyses. The second, a concentration of untreated oocysts using a Cesium chloride gradient, is suitable for biochemical and immunological studies, but requires “fresh” oocysts.

Spontaneous death of Echinococcus multilocularis: cases diagnosed serologically (by Em2 ELISA) and clinical significance.

Abstract: Nine cases of asymptomatic alveolar hydatid disease (AHD) of the liver were diagnosed in 1985 among Eskimos from the endemic region of western Alaska. The patients were identified by screening with the enzyme-linked immunosorbent assay, using purified Echinococcus multilocularis antigen (Em2 ELISA). Five patients, and one diagnosed earlier (1979), were found to have lesions in which the larval E. multilocularis had died spontaneously at an early stage of infection. Viability was assessed histologically; by the avidinbiotin immunohistochemical method; and in vivo through intraperitoneal inoculation of membranes of the larval cestode into red-backed voles, Clethrionomys rutilus. The results were in agreement with the clinical impression, based on findings by computerized tomography and ultrasound scanning, and on the macroscopic appearance of the lesions, that the cestode was dead. Spontaneous death of E. multilocularis in humans has not been previously reported. The findings show that the Em2 ELISA may be positive in patients having lesions of AHD in which the etiologic agent is no longer viable.

Cyst Rupture as a Pathogenic Mechanism of Toxoplasmic Encephalitis

Abstract: Seemingly intact cysts and sequential stages of disintegrating cysts of Toxoplasma were identified immunohistologically within developing microglial nodules in a Panamanian night monkey (Aotus lemurinus). This monkey had been successfully immunized and challenged 5 months earlier. This supports the hypothesis that glial nodules unassociated with Toxoplasma tachyzoites may represent the tombstone of a Toxoplasma cyst. Disintegration of cysts may give rise to clinical encephalitis in the presence of apparently adequate immunity.

Cysticercotic encephalitis: a severe form in young females.

Abstract: Clinical and computerized tomography findings in patients with miliary infestation of cysticerci in brain parenchyma are presented. Cysticercotic encephalitis produces a severe and frequently fatal neurological disorder. Although parenchymal cysticercosis is common in endemic areas, in the cases reported here, the pathology is induced by a severe inflammatory response in brain parenchyma rather than by the physical presence of multiple cysts. As a result of diffuse brain edema, all cases develop subacute severe intracranial hypertension and compromise of visual function. One important feature of this form of neurocysticercosis is that it particularly affects young women.

The clinical and immunologic responses of normal human volunteers to low dose hookworm (Necator americanus) infection.

Abstract: Five normal human volunteers were exposed to approximately 50 infective larvae of Necator americanus and were observed for the development of clinical signs or symptoms and for changes in blood eosinophil levels, IgG antibody titers, total and parasite-specific IgE, and lymphocyte blastogenic responses for 6-10 weeks Bronchoalveolar lavage was performed on four subjects prior to infection and at times when larval migration through the pulmonary tree was likely Eggs were demonstrated in the stools of four volunteers who remained untreated for more than 6 weeks; one volunteer had to be treated at day 40 because of severe gastrointestinal symptoms All others also complained of abdominal pain and flatulence between days 35-40 All volunteers developed marked blood eosinophilia which peaked between days 38-64 and ranged from 1,350-3,828 eosinophils/mm3 Small increases in total and parasite-specific IgE and IgG were noted in some volunteers One volunteer showed a significant lymphocyte blastogenic response With the exception of mucosal erythema, bronchoalveolar lavage results were unremarkable Our data indicate that a single small inoculum of hookworm larvae is capable of producing significant transient gastrointestinal morbidity and marked blood eosinophilia but does not induce other prominent T cell- and B cell-dependent immune responses

Dengue Hemorrhagic Fever: Diagnosis, Treatment and Control: by the World Health Organization vii + 58 pages, illustrated, World Health Organization, 1211 Geneva 27, Switzerland. 1986. $7.80

Abstract: This paperbound booklet is the second revision of a manual issued in 1975. It is relatively expensive for those countries where dengue (DEN), dengue hemorrhagic fever (DHF), and dengue shock syndrome (DSS) exist or are feared. Chapter 1, General Considerations, gives historical perspective and an idea of the dimensions of the problem. The orientation is obviously Southeast Asia, and one wonders why Australia is not mentioned in “other countries at risk.” It should be noted that the existence of DEN in West Africa was not reported until Carey and Causey in 1970 signalled its presence determined by virus isolation from children seen at a fever clinic at the University Hospital in Ibadan. Dengue virus(es) have since been isolated in several West African countries; DHF/DSS has not been reported. In subsection “Pathology” it could be mentioned that the virus is rarely isolated from blood or organs of DHF/DSS patients unless special isolation techniques are used.

Toxoplasma Encephalitis in Patients with Acquired Immune Deficiency Syndrome: Diagnosis and Response to Therapy

Abstract: Although Toxoplasma gondii is the most commonly recognized cause of central nervous system mass lesions in patients with acquired immune deficiency syndrome, published investigations have provided little information about criteria for diagnosis of toxoplasmosis or the response to therapy. In this series the method of diagnosis and response to therapy were assessed in 14 patients who had evidence for toxoplasmosis based on routine histopathology, immunoperoxidase staining, or mouse inoculation. These patients presented with clinical and radiologic findings that did not clearly distinguish them from patients with other infectious or neoplastic processes. Excisional biopsies usually showed tachyzoites on routine histology, but needle biopsies were usually negative unless mouse inoculation or immunoperoxidase staining was employed. Response to pyrimethamine and sulfadiazine therapy was often prompt, but therapy had to be continued for long periods of time to maintain a clinical response, and no alternative regimen of one or more drugs appeared to be effective in patients unable to tolerate both pyrimethamine and sulfadiazine.

Field evaluation of an enzyme-linked immunosorbent assay (ELISA) for Plasmodium falciparum sporozoite detection in anopheline mosquitoes from Kenya.

Abstract: An enzyme-linked immunosorbent assay (ELISA) using a monoclonal antibody that recognizes a repetitive epitope on the circumsporozoite protein of Plasmodium falciparum was used in Kenya to assess malaria infections in Anopheles gambiae s.l. and An. funestus. The ELISA confirmed that 88% of 44 sporozoite-positive gland dissections were P. falciparum. The ELISA infection rate of 18.6% (n = 736) for individually tested mosquitoes for both species was significantly higher than the 10.4% (n = 537) salivary gland sporozoite rate determined by dissection. This difference was due to ELISA detection of medium and large sized oocysts on the midguts of infected mosquitoes which did not contain salivary gland sporozoites. From a series of 379 Anopheles that were cut at the thorax, ELISA tests on "head" and "body" portions showed that 29.5% of 95 positive mosquitoes contained circumsporozoite antigen in the body portion in the absence of salivary gland infections. This field evaluation demonstrates that the ELISA can most accurately be used to estimate sporozoite rates by cutting mosquitoes at the thorax and testing anterior portions.

The basis of antimalarial action: non-weak base effects of chloroquine on acid vesicle pH.

Abstract: Biologically active concentrations of chloroquine increase the pH of the parasite's acid vesicles within 3-5 min. This increase in pH results from two mechanisms, one of which is markedly reduced in chloroquine-resistant parasites. Because chloroquine is a weak base, it increases vesicle pH by that mechanism in chloroquine-susceptible and resistant parasites and mammalian cells (based on its two pKs and on the delta pH between the acid vesicle and the extracellular environment). In chloroquine-susceptible parasites, but not resistant parasites or mammalian cells, chloroquine increases the pH of acid vesicles 700- to 800-fold more than can be accounted for by its properties as a weak base. The increase in acid vesicle pH caused by these non-weak base effects of nanomolar chloroquine in susceptible parasites suggests that chloroquine acts by interfering with acid vesicle functions in the parasite such as the endocytosis and proteolysis of hemoglobin, and the intracellular targeting of lysosomal enzymes. The non-weak base effects of nanomolar chloroquine on parasite vesicle pH are also responsible for its safety because these chloroquine concentrations do not affect mammalian cells.

Variation of Hepatic Fibrosis and Granuloma Size among Mouse Strains Infected with Schistosoma mansoni

Abstract: To investigate the relation between the size of circumoval granulomas and hepatic fibrosis, a variety of mouse strains infected with Schistosoma mansoni were examined and the number of eggs in the tissues, the fibrotic responses to the eggs, and the volume of the granulomas were determined. Marked differences in granuloma volume and in hepatic fibrosis were found between mouse strains, and those strains with the largest granulomas also showed the most hepatic fibrosis. On the other hand no significant correlation between granuloma size and hepatic fibrosis was found in the progeny of the F2 generation and backcrosses between F1 mice and the parental strains when crosses were made between Nmri mice (high granuloma volume and high fibrosis) and C57BL/6 mice (low granuloma volume and low fibrosis). Hepatic fibrosis per egg decreased with increasing infection intensity while granuloma volume was unaffected, indicating that fibrosis and granuloma size are at least in part modulated by different factors. The number of eggs found in the tissues per worm pair and the proportion of eggs in the liver also decreased as infection intensity increased. Some influence of the major histocompatibility complex on both granuloma size and fibrosis was found. Congenic mice on the C57BL/10 and C3H/HeSn backgrounds showed larger granulomas in H-2b than in H-2k mice, but no such correlation was found in comparing C57BL/6 mice with B6.H-2k mice. Less hepatic fibrosis was found in B10.M (H-2f), B10.SM (H-2v), and B10.RIII (H-2r) animals than in C57BL/10 mice. The regulation of granuloma size and of hepatic fibrosis is clearly complex and involves genes both outside of and within the major histocompatibility complex.

Sexual transmission of dengue viruses by Aedes albopictus.

Abstract: Male Aedes albopictus experimentally infected with dengue virus types 1, 2, 3, or 4 transmitted their infection sexually to female Ae. albopictus. Such transmission was enhanced if the females had taken a bloodmeal 2 to 7 days prior to mating. Male Ae. albopictus also transmitted dengue virus vertically to their F1 progeny. Infected progeny were found among those derived from eggs laid greater than or equal to 73 hr after mating but not among those derived from eggs laid prior to that time. This suggests that virus probably was not transmitted directly to ova but, rather, underwent prior replication in the female genital tract. Female Ae. albopictus experimentally infected with dengue type 1 virus did not transmit their infection sexually to males. This finding supports the hypothesis that male mosquitoes naturally infected with dengue virus acquired their infection vertically.

Circulating excretory-secretory antigen levels and specific antibody responses in mice infected with Toxocara canis.

Abstract: Circulatory excretory-secretory antigen levels and IgM and IgG responses to larval antigens were monitored in the serum of 20 BALB/c mice that had been given approximately 500 infective eggs of Toxocara canis by stomach tube. Other groups of mice received different doses of infective eggs, ranging from 5 to 1,250 eggs. Excretory-secretory antigens were collected from culture fluid in which mechanically hatched larvae of T. canis were maintained. An indirect enzyme-linked immunosorbent assay was used to monitor specific antibody responses. Circulating antigen levels were monitored using a direct ELISA which incorporated an IgG fraction of a rabbit antiserum to the excretory-secretory antigens as a capture antibody and a biotin-conjugated form of the same rabbit IgG as the second antibody. The antigen-specific IgM response was evident the first week of infection and peaked 3 to 6 weeks post-infection. The antigen-specific IgG response first appeared the second week of infection and peaked at 6 to 8 weeks post-infection. Both isotype levels stayed near their peak values for the remainder of the study. In the untreated sera, circulating antigen was initially evident and highest the first week of infection; the antigen concentrations dropped by the third month of infection to low, but significant, levels that persisted for the duration of the study. The administration of >25 eggs produced antigenemias. There appeared to be a positive linear trend between the number of eggs given and the amount of antigen in the circulation.

Immunodiagnosis of human fascioliasis by enzyme-linked immunosorbent assay using excretory-secretory products.

Abstract: In sera from patients with fascioliasis the enzyme-linked immunosorbent assay (ELISA) was used to detect antibody using excretory-secretory products (ES) from Fasciola hepatica adult worms. The specificity of ES-ELISA (with OD values greater than 0.38) allowed the differentiation among fascioliasis, schistosomiasis, clonorchiasis, and other human parasite infections.

St. Louis encephalitis: lessons from the last decade.

Abstract: In 1980 Reeves wrote that epidemics of St Louis encephalitis (SLE) are preventable by means of surveillance and vector abatement This view is examined in the light of epidemic activity during the last decade (1977–1986), in which 9 discrete outbreaks occurred In addition, 5 interactive factors (virus, vector, viremic host, human immunity, environmental temperature) described by Reeves as essential to the development of an SLE epidemic are reviewed in the light of recent research Although much progress has been achieved, many questions remain about SLE epidemiology and ecology Among the most important are: Do Culex pipiens complex mosquitoes play a significant role in SLE virus transmission in the western United States? Is there a sylvatic cycle of SLE virus transmission in the east-central United States? What are the most sensitive and specific predictors of SLE virus activity in the east-central United States? What are the overwintering mechanisms which assure SLE virus recrudescence, and what role does transovarial transmission of virus play?

Dracunculiasis in Africa in 1986: its geographic extent, incidence, and at-risk population.

Abstract: This paper presents a preliminary assessment of the geographic extent and estimates of the incidence and the population at risk of dracunculiasis in Africa. Nineteen countries are known to be affected, in a belt extending right across the northern part of the continent south of 18°N, and in east Africa extending almost to the equator. Annual incidence is estimated to be 3.32 million, and the at-risk population is approximately 120 million. These data provide an initial baseline on which the success of control measures now being initiated in Africa can be assessed.

Lack of attenuation of a candidate dengue 1 vaccine (45AZ5) in human volunteers.

Abstract: A dengue type 1, candidate live virus vaccine (45AZ5) was prepared by serial virus passage in fetal rhesus lung cells. Infected cells were treated with a mutagen, 5-azacytidine, to increase the likelihood of producing attenuated variants. The vaccine strain was selected by cloning virus that produced only small plaques in vitro and showed reduced replication at high temperatures (temperature sensitivity). Although other candidate live dengue virus vaccines selected for similar growth characteristics have been attenuated for humans, two recipients of the 45AZ5 virus developed unmodified acute dengue fever. Viremia was observed within 24 hr of inoculation and lasted 12 to 19 days. Virus isolates from the blood produced large plaques in cell culture and showed diminished temperature sensitivity. The 45AZ5 virus is unacceptable as a vaccine candidate. This experience points out the uncertain relationship between in vitro viral growth characteristics and virulence factors for humans.

Arbovirus isolations from mosquitoes collected during and after the 1982-1983 epizootic of western equine encephalitis in Argentina.

Abstract: Mosquitoes were collected in Santa Fe and Rio Negro provinces, Argentina, in 1982-1983 during a western equine encephalitis (WEE) epizootic. Totals of 153,084 mosquitoes from Santa Fe Province and 484 from Rio Negro Province were tested for virus in 2,351 pools. Seventeen virus strains were isolated, all from Santa Fe collections, as follows: 4 WEE, 6 Venezuelan equine encephalitis, 1 St. Louis encephalitis, 2 Antequera, 1 Maguari, 1 Melao, 1 new vesiculovirus (Calchaqui), and 1 Gamboa. The WEE virus isolates were from Aedes albifasciatus, Anopheles albitarsis, Mansonia species, and Psorophora pallescens. Collections during the spring and summer (1983-1984) following the epizootic yielded 49,707 mosquitoes from Santa Fe, 15,961 from Rio Negro, and 2,019 from Chubut provinces. Twenty-two virus strains were isolated, all from Santa Fe mosquitoes, as follows: 3 strains of SLE virus and 19 strains of Turlock (TUR) virus. All but one of the TUR virus isolates appear to have come from mosquitoes that engorged on a viremic chicken following entry into a bait trap. The vector relationships of each virus isolated during and after the WEE epizootic are discussed.

Comparative Sensitivity and Specificity of ELISA and IHA for Serodiagnosis of Strongyloidiasis with Larval Antigens

Abstract: Sera from 68 patients with parasitologically proven strongyloidiasis were tested by the ELISA and IHA tests using larval antigens prepared from Strongyloides stercoralis and Strongyloides ratti. The ELISA using the S. stercoralis antigen detected the greatest number of sero-reactors (83.8%), whereas the IHA using the S. ratti antigen detected the fewest (55.9%). In addition, the S. stercoralis antigen had higher geometric mean titers than the S. ratti antigen in both the ELISA and the IHA tests. Sera from 37 presumed normal individuals also were tested by IHA and ELISA and nonspecific reactions were seen only with the IHA test. When sera from patients with parasitic infections other than strongyloidiasis were tested, the only consistent cross-reactions were with those sera from patients who had occult filariasis and acute schistosomiasis.

Lyme disease and babesiosis: acaricide focused on potentially infected ticks.

Abstract: Permethrin-treated cotton, intended as rodent nesting material, was distributed in wooded sites in which the agents of Lyme disease and babesiosis were enzootic, in order to kill immature Ixodes dammini, the ticks that transmit these human pathogens. Such ticks feed most abundantly on white-footed mice (Peromyscus leucopus), apparently the main reservoir hosts of these agents, and tend to concentrate in mouse burrows. Mice captured after permethrin-treated cotton was distributed, were infested by a tenth as many ticks as were those captured in adjacent nontreated sites, a difference that continued throughout the 4-month period of observation. On average, 72% of all mice captured in treated sites were free of ticks, while virtually all mice captured in nontreated sites were infested. Voles (Microtus pennsylvanicus), however, were tick-infested, regardless of site of capture. Laboratory-reared I. dammini failed to attach to mice captured in treated sites, and most such exposed ticks died. Distribution of permethrin-treated cotton appears to be a means for preventing transmission of the pathogens that cause human babesiosis and Lyme disease.

Lyme Disease Ecology in Wisconsin: Distribution and Host Preferences of Ixodes dammini, and Prevalence of Antibody to Borrelia burgdorferi in Small Mammals

Abstract: Lyme disease recently has been recognized in Wisconsin. Trapping studies were conducted at four geographically separate and ecologically distinct regions in Wisconsin to elucidate the distribution and host preferences of Ixodes dammini on small and medium sized mammals, and the occurrence of antibodies to Borrelia burgdorferi in these wild mammals. Peak I. dammini larval activity occurred from June–September. Nymphs were most active from May–August. White-footed mice (Peromyscus leucopus) and chipmunks (Tamias striatus) were important hosts for immature ticks. Mean numbers of I. dammini per mouse were highest in regions of high prevalence of Lyme disease. Antibody to B. burgdorferi was detected in sera of 60/371 (16%) white-footed mice, 5/104 (5%) chipmunks, 3/5 (60%) gray squirrels (Sciurus carolinensis), 0/8 raccoons (Procyon lotor), and 0/12 opossum (Didelphis virginiana); antibody prevalence correlated positively with I. dammini occurrence, and seropositive animals were not detected in areas where I. dammini were not found. Two of 15 recaptured P. leucopus had ≥4-fold changes in antibody titer. B. burgdorferi was cultured from blood of a P. leucopus captured in west-central Wisconsin, and was observed by direct immunofluorescence in 9/23 (39%) I. dammini nymphs. In Wisconsin, I. dammini has increased in numbers and has significantly expanded its range since its first recognition in 1968.

Transovarial and transstadial passage of Borrelia burgdorferi in the western black-legged tick, Ixodes pacificus (Acari: Ixodidae).

Abstract: Transovarial and transstadial passage of Borrelia burgdorferi was demonstrated for the first time in the western black-legged tick, Ixodes pacificus. One of three field-collected females with spirochetes in ovarial tissues produced 100% infected progeny that maintained the spirochetes transstadially and in 4 of 5 cases passed them via eggs to as many as 97% of F2 filial ticks. The progeny infected ovarially and by subsequent transstadial passage had generalized tissue infections that exhibited reduced immunofluorescence staining reactivity with a fluorescein isothiocyanate-labeled polyclonal antibody. Attempts to isolate the spirochete from ticks in BSK medium or various modifications of it were unsuccessful. Spirochetes in tissue smears of all three parasitic stages of the F1 generation were nonreactive with a monoclonal antibody (H5332) specific for B. burgdorferi, whereas those present in tissue smears of F2 larvae bound with it.

Comparison of two antigenically distinct Giardia lamblia isolates in gerbils.

Abstract: Previous studies established that some isolates of Giardia differ antigenically. In order to determine if antigenic differences resulted in altered biological behavior of host immune responses, two antigenically distinct isolates, WB and GS-E, were used to infect gerbils, and the course of infection, resistance to reinfection, and host humoral responses were measured. Maximum numbers of trophozoites were recovered on day 14 from the intestine of gerbils infected with both isolates, but by day 28, 75% of WB-infected gerbils were free of infection, while GS-E-infected animals continued to be infected until day 42. After curative metronidazole therapy, animals were challenged with the homologous or heterologous isolates. Gerbils previously infected with WB were resistant to challenge with WB and GS-E, while previously GS-E-infected gerbils were more resistant to challenge with the homologous isolate. Antibody responses were measured by ELISA to both surface and cytosol antigens and by IFA to the surface of Giardia. By IFA there was a greater reactivity using the homologous isolate, but with ELISA this was not as apparent. Complement independent cytotoxicity of sera was additionally tested against both isolates. Sera from WB-infected gerbils were cytotoxic to both WB and GS-E whereas sera from GS-E-infected gerbils were cytotoxic to GS-E only. These studies demonstrate that Giardia possessing different surface antigens have different patterns of infection and induce qualitatively and quantitatively different immune responses. Cytotoxicity of sera, most likely antibodies, correlated best with the development of resistance.