The American Journal of Tropical Medicine and Hygiene - Volume 58, Issue 2, 1998

There are two principal rationales for doctoral training of African scientists in health: 1) these scientists are essential for the nations of sub-Saharan Africa to define and implement their own health priorities, and 2) the research they perform is essential for development. However, this training is difficult because of its expense (> $20,000 per year), because many developed country mentors are unaware of the realities of research in sub-Saharan Africa, and because major differences in salary provide a financial disincentive to return. We describe a training strategy that reduces attrition because it is linked to the investigators' responsibilities before and after training, and to home country priorities. This strategy requires a close relationship between the developing country (on-site) and developed country (off-site) mentors, with joint participation in the selection and funding process, followed by course work and short-term, independent projects off-site that lead to a thesis project in the developing country, and subsequently to a defined professional position in the developing country after completion of the doctoral degree. For this strategy to succeed, the developed country mentor must have both field experience and investigative expertise; the developing country mentor must have an understanding of modern biology, as well as clinical and epidemiologic experience. In addition, we would like to emphasize that the long-term retention of these talented, highly-trained individuals requires a similar long-term commitment by their developed country mentors, well beyond the short term of most research funding.

Among the many reported applications of the detection of antibodies to phenolic glycolipid-I (PGL-I) of Mycobacterium leprae, in particular, the use of seroprevalence as an indicator of the magnitude of the leprosy problem may turn out to be very useful in leprosy control programs. An operational function of serology within the leprosy control services requires a simple test system. We have developed a simple dipstick assay for the detection of antibodies to PGL-I and compared its performance with that of an ELISA. A high degree of agreement (97.2%) was observed between the ELISA and the dipstick assay when tested on 435 sera; the agreement beyond chance (Kappa value) was 0.92. No significant difference was found between the dipstick assay and the ELISA when seropositivity rates obtained in groups of leprosy patients, household contacts, and controls were compared. The interpretation of the dipstick results as positive or negative was unequivocal, as illustrated by the high agreement between different persons reading the test (Kappa values > 0.88). Storage of the only reagents required, the dipsticks and the stabilized detection reagent, up to three weeks under tropical conditions of high temperatures, high humidity, and exposure to light, did not influence the results of the assay. The dipstick assay described here is an easy-to-perform method for the detection of IgM antibodies to PGL-I of M. leprae; it does not require any special equipment and the highly stable reagents make the test robust and suitable for use in tropical countries. An internal control validates the performance of the assay. This dipstick assay may be the method of choice for epidemiologic mapping of leprosy.

Heat-shock proteins of the 70-kD (hsp70) family are targets of humoral and cellular immune responses following bacterial or parasitic infections, including Chagas' disease. In the present study, we measured antibodies in human sera reactive with hsp70s from the cytoplasm (cy-hsp70), mitochondrion (mt-hsp70), and endoplasmic reticulum (grp78) of Trypanosoma cruzi. Of the three hsp70s tested, only grp78 detected T. cruzi infection in more than 90% of nontreated (NT) patients, with cy-hsp70 and mt-hsp70 detecting only 78% and 25% of NT patients, respectively. Reactivity of leishmanial sera was 77% with cy-hsp70, 13% with grp78, and 5% with mt-hsp70. Therefore, considering sensitivity and specificity, the best candidate for T. cruzi serodiagnosis is grp78. Combination of grp78 with a T. cruzi 24-kD flagellar calcium binding protein (FCaBP) increased the diagnostic sensitivity from 90% to 97% but increased leishmanial reactivity from 3% to 8%. To determine whether hsp70s are useful for discriminating between cured and noncured patients treated with trypanocidal drugs, we tested sera from treated noncured (TNC) patients and cured patients who have positive conventional serology, termed treated dissociated (TD). The cy-hsp70 and grp78 reacted with 74% and 68% of TNC patient sera, respectively, but these antigens did not discriminate TNC from TD patients (52% and 45% positive, respectively). The mt-hsp70 was detected by sera from few TNC patients (18%) and no TD patients. Although individual hsp70s were not useful for determining the effect of trypanocidal drugs on T. cruzi infection in individual patients, the majority of TNC patient sera (70-80%) reacted with two or three of the hsp70s. In contrast, no TD sera reacted with all three hsp70s, and 40% did not react with any of the hsp70s, indicating that the number of hsp70s detected decreases following successful treatment. Considered together, these results show that grp78 has potential as a diagnostic antigen and that absence of reactivity to all three hsp70s may be indicative of effective treatment.

To increase the specificity of dengue (DEN) diagnosis based on antibody detection, we have evaluated recombinant proteins as antigens that incorporate most of the B domain of the DEN virus envelope protein fused to the trpE protein of Escherichia coli (trpE-DEN). A pooled antigen consisting of trpE-DEN proteins representing all four serotypes of DEN virus was used in an indirect ELISA for the detection of IgG or IgM antibody. This assay was compared with a standard IgG indirect ELISA and an IgM-capture ELISA using DEN virus-infected cell culture pooled antigens. The results indicated that the trpE-DEN antigens and the cell culture antigens were equally sensitive for detecting IgM and IgG antibodies in convalescent sera from Peru and Indonesia representing virus isolation-confirmed primary and secondary DEN infections, respectively. Fourteen day postinfection IgG antibody-positive sera obtained from individuals infected with DEN-1 virus who had been vaccinated with other flaviviruses were more strongly reactive with the cell culture antigen than with the recombinant antigen, but by day 21 postinfection, a strong antibody response to the trpE-DEN antigens was present. These results suggested that the early antibody response was directed predominantly towards shared flavivirus group antigens that were not detected with the trpE-DEN antigens. Comparison of the trpE-DEN-1 recombinant antigen with a DEN-1 virus-infected cell lysate antigen for the detection of IgG antibody in sera from a cohort of 55 individuals from Peru who seroconverted over a one-year period indicated greater specificity for the recombinant antigens. Also, sera from individuals with no known DEN infections that had been sequentially vaccinated with yellow fever and Japanese encephalitis reacted with the DEN virus cell culture antigen in the IgG ELISA, but did not react with the trpE-DEN pooled antigens. Similarly, YF IgM antibody positive samples that showed cross-reactivity with the DEN virus cell culture antigens, did not react with the trpE-DEN pooled antigens. These results indicated that the trpE-DEN pooled antigen provided a more specific diagnosis of dengue infections than DEN virus-infected cell culture antigen and avoided the biohazards associated with handling live virus during the preparation of diagnostic reagents. The trpE-DEN pooled antigen should permit a better approach to distinguish between past DEN and other flavivirus infections in epidemiologic surveys, and also increase the specificity of serologic diagnosis of acute DEN infections.

The polymerase chain reaction (PCR) was used to detect the presence of Paracoccidioides brasiliensis in a murine model of disseminated paracoccidioidomycosis. Using a previously identified P. brasiliensis-specific DNA sequence, P. brasiliensis DNA was detected in serum of five experimentally infected mice. The PCR method was able to detect as little as 10 pg of P. brasiliensis DNA in serum, and it was more sensitive than blood culture isolation (five of five were PCR positive versus two of five blood culture positive). There were no amplified fragments in serum from three noninfected control mice. Lung colony counts were similar in all infected mice and reflected a similar degree of P. brasiliensis infection at the time the samples were drawn. The relatively short processing time for the PCR, when compared with culture, its sensitivity, and the possibility of using serum samples for analysis, are important factors favoring this method for the diagnosis of paracoccidioidomycosis. Future studies should include the detection of P. brasiliensis in patients with different clinical forms of paracoccidioidomycosis.

Serum samples collected from 237 dogs in Catalonia (northeastern Spain) were screened by Western blot analysis to detect the presence of antibodies specific to different Leishmania infantum polypeptide fractions. Leishmaniasis was confirmed in 72 of these dogs by direct examination and/or culture. Another 165 animals from the Priorat region were studied periodically for 2-8 years between 1987 and 1995, giving a total of 565 determinations. A control group of 93 dogs from nonendemic areas was also studied. Sera from dogs with leishmaniasis recognized antigens with molecular weights ranging from 12 to 85 kD. The most sensitive antigens were those of 70, 65, 46, 30, 28, 14, and 12 kD, which were recognized by 75%, 75%, 78%, 75%, 81%, 79%, and 75%, respectively, of the sera from dogs with positive parasitologic examination results. Antigens of 70 and 65 kD were also recognized by two dogs from nonendemic areas. Antigens of 14 and 12 kD were the first to be recognized by sera of asymptomatic dogs with titers less than the cut-off value of the dot-ELISA that increased during the longitudinal study, and the presence of antibodies specific for these fractions was observed for up to six years before seroconversion observed by dot-ELISA. These antibodies were also the first to disappear in dogs in which the disease was self-limited. The study corroborates the high sensitivity and specificity of Western blots in the diagnosis of canine leishmaniasis when the bands of low molecular weight (less than 46 kD) are considered, and indicates that fractions of 14 and 12 kD are useful in detecting early forms of the disease.

An outbreak of zoonotic cutaneous leishmaniasis (ZCL) occurred in a battalion of 80 soldiers posted at Qurayqira camp in Wadi Araba in southern Jordan. The battalion spent an intermittent period of five and a half months in the area, during which 45.0% (36 of 80) of the soldiers showed clinical disease. Of the 44 clinically negative soldiers, 31 were tested with leishmanin and 11 (35.5%) were leishmanin positive. The number of lesions in infected soldiers ranged from one to 15 and were mostly on the face and extremities. This report shows the level of transmission of ZCL in Wadi Araba, which is presently undergoing economic expansion and development following the peace process of the Arab-Israeli conflict.

A total of 127 strains of Vibrio cholerae (117 V. cholerae O1 and 10 nonagglutinating strains) isolated from a recent cholera outbreak in Senegal and four strains isolated in Guinea-Bissau (during the survey of a cholera epidemic that occurred 10 months before the Senegalese one) were analyzed. Strains were characterized by conventional methods (biochemical and serologic identification, susceptibility to antimicrobial agents), polymerase chain reaction for genes encoding cholera toxin (CtxA), zonula occludens toxin (Zot), and accessory cholera enterotoxin (Ace), and by ribotyping. Conventional methods showed that all strains of V. cholerae O1 belonged to serotype Ogawa, biotype El Tor and were resistant to the vibriostatic agent O129 (2,4-diamino 6,7-diisopropylpteridine phosphate), cotrimoxazole, and chloramphenicol; all strains were sensitive to tetracycline, a drug that has been extensively used in cholera therapy. Most of these V. cholerae O1 (112 strains from Senegal and four strains from Guinea-Bissau) had an intact core region (virulence cassette) and amplified a 564-basepair (bp) fragment of ctxA, a 1083-bp fragment of zot, and a 314-bp fragment of ace. Ribotyping of V. cholerae O1 strains after Bgl I restriction of total DNA revealed that ribotype B5a, which is the predominant ribotype of this seventh pandemic of cholera, was not isolated. Instead, a new ribotype was identified and designated B27 in our data bank. Since O1 isolates from Guinea-Bissau and Senegal have the same biotype, serotype, and ribotype and as the Guinea-Bissau outbreak that preceded the one in Senegal, this emerging ribotype probably came from Guinea-Bissau. Nonagglutinating strains exhibited no resistance to the O129 agent and to the tested antibiotics, they were all negative for virulence cassette, except for one strain with the ctxA and zot genes isolated from a patient with diarrhea, and there was a great variability of ribotypes among these strains. There was no difference between environmental O1 strains isolated from water and strains isolated from patients with cholera, suggesting that fecally contaminated water is an important reservoir for infection.

The effect of La Crosse (LAC) virus infection on Aedes triseriatus overwintering success was determined. Eggs from LAC virus transovarially infected (LAC TOT+) and uninfected (LAC TOT-) Ae. triseriatus colonies were induced into diapause, held in natural conditions, and returned to the laboratory at predetermined times for assay of diapause, mortality, and filial infection rates, and to examine viral transcription and replication during diapause. Embryos from the LAC TOT+ colony exhibited greater cumulative mortality (16.7%) than the LAC TOT- eggs (7.3%) throughout the overwintering periods. The increased mortality rate in LAC TOT+ eggs corresponded with a decrease in filial infection rates. Eggs from the LAC TOT+ colony terminated diapause more readily than the LAC TOT- colony. An RNA strand-specific reverse transcriptase-polymerase chain reaction technique was used to monitor viral transcription and replication in mosquito eggs during overwintering, and to compare viral replication in diapausing and nondiapausing embryos. Viral messenger and replicative form RNA were present in eggs in all sample periods, suggesting that some virus replication occurred during diapause.

Using serum or infected blood from Danish volunteers and Plasmodium falciparum-infected Mozambican patients, respectively, the impact of curative doses of chloroquine and pyrimethamine/sulfadoxine upon infectivity of P. falciparum to Anopheles arabiensis and An. gambiae or of P. berghei to An. stephensi was studied. Both treatments cleared circulating P. falciparum gametocytes within 28 days. Before this clearance, chloroquine enhanced infectivity to An. arabiensis, whereas pyrimethamine/sulfadoxine decreased infectivity. Patients harboring chloroquine-resistant parasites as opposed to -sensitive ones were 4.4 times more likely to have gametocytes following treatment. In contrast, pyrimethamine/sulfadoxine-resistant parasites were 1.9 times less likely to produce gametocytes. In laboratory infections using replicated P. berghei or P. falciparum preparations, serum from chloroquine-treated, uninfected, nonimmune volunteers enhanced gametocyte infectivity with increasing efficiency for 21 days following treatment, whereas pyrimethamine/sulfadoxine significantly suppressed infectivity. The observed enhancement in infectivity induced by the use of chloroquine combined with increased gametocytemias in chloroquine-resistant strains may in part explain the rapid spread of chloroquine resistance in endemic populations.

The therapeutic efficacy and the incidence of early antivenom reactions (EARs) were compared in a clinical trial performed in 79 patients bitten by Bothrops sp. in Urabá, Colombia. Patients were randomized into three groups according to the antivenom administered: A (n = 30, Butantan polyspecific, pepsin-digested Bothrops antivenom); B (n = 27, Butantan polyspecific, whole IgG Bothrops antivenom); and C (n = 22, Colombian commercial, monovalent, whole IgG Bothrops antivenom). The groups were comparable in all clinical and epidemiologic aspects; 33 patients had mild, 22 moderate, and 24 severe envenoming. At the doses used (two, four, and six vials [10 ml/vial] for mild, moderate, and severe envenomings, respectively) there were no differences between the antivenoms in restoring normal hemostatic parameters within 24 hr. The evolution of local envenoming was comparable in the three groups. Serum venom/antivenom kinetics determined by ELISA showed a complete clearance of venom levels 1 hr after treatment in mild/moderate envenomings. In severe cases, venom levels remained detectable up to 24 hr and recurrence of antigenemia was observed in some cases. Antivenom concentrations remained at high levels up to 24 hr of treatment. The incidence of EARs was significantly different in the groups: A (36.7%), B (11.1.%), and C (81.8%). There were no life-threatening anaphylactic reactions. We conclude that the efficacy of the three antivenoms was similar in neutralizing human Bothrops envenomings and that the production of whole IgG antivenoms by caprylic acid fractionation is a good alternative for reducing the incidence of EARs.

Seventy-three cases of acute brucellosis were studied in relation to fever duration and hospital stay following different drug combinations, including gentamicin plus cotrimoxazole, rifampicin plus doxycycline, rifampicin plus cotrimoxazole, rifampicin plus tetracycline, streptomycin plus doxycycline, doxycycline plus cotrimoxazole, tetracycline plus cotrimoxazole, and tetracycline plus streptomycin. No statistical significant difference was found between these combinations regarding early clinical response in human brucellosis.

Leishmaniavirus is a double-stranded RNA virus that persistently infects some strains of the protozoan parasite Leishmania. There is considerable interest in the possibility that the presence of this virus alters parasite phenotype and may affect disease pathogenesis. If so, the virus marker could provide a valuable prognostic indicator for human leishmaniasis, particularly in those cases caused by New World parasite strains. The virus has been detected in cultured L. braziliensis, L. b. guyanensis, and L. major. To date there has been no information as to the extent of infection in samples prior to culturing in the laboratory. This study demonstrates, through the reverse transcription-polymerase chain reaction, that Leishmaniavirus exists in human biopsy samples of leishmaniasis prior to manipulation in culture.

Genetic analysis of the number of Plasmodium falciparum genotypes per infected person in regions of holoendemic and hyperendemic malaria suggest that in areas of lower transmission intensity, significantly fewer parasite genotypes per infected person should be found. A predominance of single clone infections in the human population could generate the controversial clonal population structure proposed for P. falciparum by Tibayrenc and others. Characterization of P. falciparum from individuals on the Thai-Burmese border, an area of hypoendemic transmission, revealed a higher number of genotypes per infected person than that predicted. Possible reasons for this observation are discussed, with particular attention paid to human migration and multidrug resistance.

Clinical immunity to malaria was studied by quantifying the intensity of symptoms as well as by measurement of several hematologic indicators of pathology (the erythrocyte sedimentation rate [ESR], serum bilirubin, reticulocyte count, plasma tumor necrosis factor-alpha [TNF-alpha], and blood glucose levels) in 39 Plasmodium vivax malaria patients exposed to endemic malaria in southern Sri Lanka, and for comparison in 43 nonimmune patients who were residents of nonmalarious regions of the country. The intensity of 11 symptoms was scored numerically in all patients using a questionnaire. This clinical score was validated by introducing internal controls to the questionnaire, and by correlating it with the underlying pathology. Both the intensity of clinical disease as well as the degree of underlying pathology were found to be significantly lower in endemic area patients (mean clinical score = 8.8, median ESR = 8 mm) compared with the nonendemic area patients (mean clinical score = 19.0, median ESR 31.5 mm). Endemic area patients also had lower parasite densities (mean = 0.06%) than those from the nonendemic area (0.12%) (P < 0.05). However, at any parasite density, both clinical disease and pathology were significantly less in the endemic area patients (P < 0.001, for both clinical score and ESR), indicating that the clinical immunity seen in the endemic area patients was a true tolerance of parasites. Although plasma TNF-alpha levels were elevated in both groups of patients, they were significantly higher in the nonendemic area patients than in patients from the endemic area (P < 0.01). Furthermore, at comparable levels of plasma TNF-alpha, nonendemic area patients had both a higher intensity of clinical disease and an underlying pathology than those from the endemic area, suggesting that if TNF-alpha is indeed a mediator of clinical disease, the endemic area patients may be tolerant to its effects. Hypoglycemia was not observed in any of these P. vivax patients despite some with high levels of plasma TNF-alpha.

This study was aimed at delineating characteristics of naturally acquired immunity against the merozoite surface antigen-1 (MSP-1) of Plasmodium falciparum, a candidate malaria vaccine antigen. A case/control study was performed on 75 case/control pairs of infants with febrile illness at the time of the first detected infection indicating a clinical case. The presence and level of antibodies at one month prior to the first infection and at the time of the first infection in the afebrile group was significantly higher than in the febrile group. Decreased parasite density and decreased infection-related loss of hemoglobin was seen in infants with anti-MSP-1(19kD) IgG antibodies. In addition, mothers who were positive for the presence of these antibodies conferred protection against placental infection and infection in their infants. In this study, development of anti-MSP-1(19kD) antibody responses in 24 infants were studied longitudinally using monthly serum samples collected from birth until approximately one year of age. In addition, umbilical cord blood sera and respective mothers' sera were analyzed. Longitudinal studies of antibody responses revealed several short-lived IgG and IgM peaks throughout an infant's first year that correlated with detection of parasitemia. The protection against parasitemia and febrile illness was observed in infants when anti-MSP-1(19kD) antibodies were present; when infants were negative for IgG, they had a 10-times greater risk of becoming parasitemic. These data from a longitudinal and prospective study of malaria suggest a protective role for anti-MSP-1(19kD) antibodies in infants and pregnant women.

The humoral immune response against synthetic peptides of two Plasmodium falciparum blood-stage antigens, Pf155/ring-infected erythrocyte surface antigen (RESA) (EENV)6 and Pf332 (SVTEEIAEEDK)2, in individuals belonging to three sympatric ethnic groups (Mossi, Rimaibe, and Fulani) living in the same conditions of hyperendemic transmission in a Sudan savanna area northeast of Ouagadougou, Burkina Faso were examined. The Mossi and Rimaibe are Sudanese Negroid populations with a long tradition of sedentary farming, while the Fulani are nomadic pastoralists partly settled and characterized by non-Negroid features of possible Caucasoid origin. A total of 764 subjects (311 Mossi, 273 Rimaibe, and 180 Fulani) were tested. A lower P. falciparum prevalence was observed in the Fulani of all age groups. The serologic results clearly indicate the existence of interethnic differences in the capacity to respond to these two P. falciparum antigens. The Mossi and Rimaibe showed similar responses, whereas the Fulani displayed consistently higher prevalences and levels of antibodies against both epitopes tested. The anti-(EENV)6 and anti-(SVTEEIAEEDK)2 seroprevalences were 29.9% and 38.9% in Mossi, 29.7% and 39.2% in Rimaibe, 86.1% and 76.1% in Fulani (all P values of Fulani-Mossi and Fulani-Rimaibe comparisons < 0.001). Anti-RESA and anti-Pf332 antibody levels were approximately 65% (P < 0.001) and 45% (P < 0.001), respectively, higher in seropositive Fulani than in seropositive Mossi and Rimaibe, who showed very similar values. The observed differences cannot be explained in terms of interethnic heterogeneity of malaria exposure since these communities have lived in the same area for more than 30 years and the P. falciparum inoculation rate, measured during two consecutive years, was substantially uniform for the three ethnic groups. The possibility of remarkable heterogeneities in the capacity to mount immune responses against P. falciparum antigens among populations with different genetic backgrounds must be taken into account in the development of anti-malaria vaccines.

Variant- and strain-specific immunity to malaria in Saimiri monkeys infected with homologous O and R variants of the Palo Alto strain (FUPSP) of Plasmodium falciparum or by various heterologous divergent strains were studied. Following homologous reinfections, the primary immune response in monkeys was effective only against the same variant type but not against the other variant, which differed only by antigens exposed at the surface of the infected red blood cell. In contrast, after two successive inoculations with a single variant type, a variant transcending immunity developed to both O and R parasite populations. The immunity against FUPSP in monkeys repeatedly infected with various combinations of heterologous strains, including Sal I, Tanzania, Camp, FUPCP, FCH4, FVO, and FUPCDC parasites was less effective, resulting at best in protecting the monkey against fulminating infection. However, in several cases, previous or concomitant heterologous infections modified the course of virulent infection by FUPSP parasites, indicating a significant degree of cross-protection between the strains. Therefore, in this model, while variant- and strain-specific antigens are important components of acquired immunity to malaria, the monkey immune response to infection transcends phenotypic antigenic variation and strain diversity.

The circulating anti-parasite antibody response against Giardia lamblia in symptomatic and asymptomatic Egyptian children with confirmed giardiasis was examined. Symptomatic patients were identified using the following criteria: presence of only G. lamblia cysts in the feces, and one or more of the following symptoms, diarrhea, abdominal pain, loss of weight, vomiting and/or nausea, and abdominal distention. The anti-parasite humoral response was measured using indirect immunofluorescence (IFA), ELISA, and immunoblotting. There was a significant difference in the anti-parasite antibody response measured by IFA of asymptomatic and symptomatic patients, in which more than 34% of the asymptomatic patients had a titer equal to or less than 1:500, and more that 29% of the symptomatic patients had a titer of 1:8,000 or higher. The circulating anti-parasite total IgM and IgA but not IgG, measured by ELISA, was significantly higher in symptomatic than in asymptomatic patients, and were related to higher cyst output observed in symptomatic individuals. Although total anti-parasite IgG response was similar in symptomatic and asymptomatic patients, the analysis of the IgG isotype responses revealed that both IgG1 and IgG3 were significantly higher in symptomatic patients. The antigen recognition by anti-parasite IgM, IgA, IgG1, and IgG3 of symptomatic and asymptomatic individuals, determined by immunoblotting, was heterogeneous and revealed only minor differences in the response of the two groups.