The American Journal of Tropical Medicine and Hygiene - Volume 44, Issue 2, 1991

We collected 1180 sera and 1363 questionnaires with information on demography, rodent exposure, and history of travel from persons visiting a sexually transmitted disease (STD) clinic in Baltimore between 1986–1988. Serological tests for two rodent-borne viruses detected antibodies to lymphocytic choriomeningitis virus (LCMV) in 54 individuals (4.70%; n=1149)and antibodies to Seoul virus (SEOV) in three persons (0.25%; n=1180). Antibody prevalence to LCMV increased with age, but there were no racial or sexual differences. Neutralization tests and questionnaire responses implicated a domestic, rat-borne hantavirus as the source of SEOV antibody. Self-reported humanrodent contact indicated more exposure to house mice than rats within residences, although rats were more commonly sighted on streets. Infections with rodent-borne viruses were rare compared to the high rates of reported contact.

To ascertain the prevalence of human T-lymphotropic virus type I (HTLV-I) infection and the occurrence of diseases caused by HTLV-I in the Solomon Islands, we tested 1141 sera from 851 patients (317 females and 534 males), who were hospitalized at the Central Hospital in Honiara between February 1984 and November 1988, for antibodies to HTLV-I using an enzyme-linked immunosorbent assay (ELISA). Sera from 69 of 81 ELISA-positive patients and from 56 ELISA-negative patients were then tested by Western analysis. As verified by strict Western immunoblot criteria, the overall HTLV-I seroprevalence was 2.2% (19/851). Age- and gender-specific prevalence data indicated an age-related acquisition of infection with no sexual predominance. No diagnosis category was over-represented among the seropositive patients. HTLV-I-specific antibodies were found in serum and cerebrospinal fluid samples from one of six patients with spastic paraparesis. As in other Melanesian populations, the majority of ELISA-positive sera could not be confirmed by Western analysis. Reactivity to three or more gag-encoded proteins was found in 85% (45/53) of ELISA-positive, Western blot-indeterminate sera, and 30% (16/53) reacted to p19 and an env gene product but lacked reactivity to p24. Whether or not the high frequency of indeterminate HTLV-I Western immunoblots in the Solomon Islands is indicative of incomplete specific reactivity to HTLV-I or the existence of antigenically related retroviruses is being investigated.

We studied the potency, antibody response, and side reactions of commercial Japanese chick embryo cell (CEC) rabies vaccines for humans. The CEC rabies vaccines had indexes of 105.1 and 106.0 in Habel tests, and have had potencies higher than those of the International Reference Vaccine II by National Institutes of Health (NIH) tests. Thirty healthy adults received 1 ml of the CEC rabies vaccines subcutaneously as primary immunization on days 0 and 7. Between six and 12 months after the primary immunization, 22 of the 30 subjects showed neutralizing antibody levels ≥1:40 by the rapid fluorescent focus inhibition test (RFFIT). The 30 subjects had been given booster immunizations of the CEC rabies vaccines at 8–14 months in addition to the primary immunization. Six to 12 months after the booster immunizations, 27 of the 30 subjects showed antibody levels ≥1:40. No severe side reactions were reported during the course of vaccination. Thus we conclude that CEC rabies vaccine is effective and safe for pre-exposure immunization.

Various routes of Borrelia burgdorferi infection were studied in laboratory rats. Three-week-old Lewis rats were inoculated either intradermally (i.d.), intraperitoneally (i.p.), or oronasally (o.n.) with serial 10-fold dilutions of B. burgdorferi. Thirty days later, groups of rats were killed and serology, splenic culture, and histology were used to evaluate infection. Rats were successfully infected i.d. with 102–4 organisms or i.p. with 104–5 organisms. Neither three-day-old nor three-week-old rats were successfully infected o.n. with up to 106 organisms. For contact transmission, three-day-old or three-week-old inoculated rats were housed with unexposed littermates for 30 days. Inoculated rats became infected but contact rats remained free of infection. To study in utero transmission, five pregnant female Lewis rats were inoculated i.p. with 106 spirochetes at four days gestation. Although adult females seroconverted or had positive splenic cultures at 20 days gestation, the placentas and fetuses were uniformly culture-negative. Venereal transmission from seven infected females or six infected males to uninfected rats of the opposite sex was not demonstrated.

Monoclonal antibody-based enzyme-linked immunosorbent assay and DNA hybridization techniques were developed and evaluated for their potential in the detection of Opisthorchis viverrini infection in humans. A mixture of three IgG1 monoclonal antibodies (MAb) specific for the 89 kDa metabolic product of O. viverrini was captured on a microtiter plate by rabbit anti-mouse IgG and used in a sandwich ELISA for the detection of parasite antigen. The 89 kD component bound to the MAb was detected with biotinylated rabbit IgG antibody to O. viverrini metabolic products. As little as 0.05–0.1 ng of the antigen could be detected by this technique. A specific O. viverrini DNA probe constructed from a repetitive DNA segment containing 340 base pairs was used in a dot blot hybridization for the detection of parasite DNA. The labeled probe constructed as such could detect DNA released from as few as five O. viverrini eggs. Both methods were specific for O. viverrini and their sensitivity was comparable with that of the classical parasitological technic.

Sparganosis, infection with plerocercoids of the pseudophyllidean tapeworm Spirometra, rarely has been described in Ecuador. We report the details of a human case of sparganosis identified serendipitously in the course of an abdominal hernia repair. The parasite was found moving freely upon the external oblique fascia adjacent to the site of a direct abdominal hernia. The organism was recovered intact, photographed while alive and preserved for subsequent detailed morphological studies. The presumed route of entry into this patient was percutaneous, after application of a poultice of snake flesh to the site of a painful abdominal hernia. The literature on sparganosis in South America is reviewed. This is the second case of human sparganosis reported from Ecuador.

Three chimpanzees, three mangabey monkeys (Cercocebus atys), and 14 patas monkeys (Erythrocebus patas) were inoculated with L3 Onchocerca volvulus of Guatemalan origin. One chimpanzee and two mangabey monkeys developed antibody activity to at least three different antigens. Both mangabey monkeys recognized a 20 kDa antigen 3.5–5 months post-inoculation, and the monkeys and the chimpanzee developed antibody activity to 14 and 22 kDa antigens 7.5–13 months post-inoculation. One mangabey monkey and the chimpanzee became microfilaria-positive in skin snips at 16 and 21 months post-inoculation, respectively. Antibody activity to the 20 kDa antigen in the mangabey monkeys is noteworthy because of the prominence of this antigen among putatively immune persons living in onchocerciasis-endemic areas. The two mangabey monkeys responded parasitologically in a manner comparable to immune humans. No microfilariae were detected in one monkey and only scant numbers of microfilariae were observed in the second. The mangabey monkey may be a good animal model for the study of onchocerciasis.

Previous studies of antifilarial antibodies in a pediatric population residing in an area with endemic Wuchereria bancrofti filariasis have demonstrated age related shifts in antifilarial immunity. To further characterize humoral responses in Haitian children, serum samples from 129 patients (3 months- 15 years of age) were analyzed by ELISA for isotype-specific antifilarial antibody responses. Age-stratified analysis of geometric mean antibody titers showed significant increases in antibody titers of all isotypes with age in the amicrofilaremic population. Antifilarial IgG1, 2, and 3 levels were higher in amicrofilaremic children than in microfilaremic children, significantly so for IgG2 and IgG3. In contrast, IgG4 antibody levels were higher in microfilaremic subjects than in amicrofilaremic subjects. A multivariate, unconditional, logistic regression model was developed from these data to predict infection status. The model correctly classified 91.6% of the amicrofilaremic subjects, but only 55.6% of the microfilaremic subjects.

Thirty-nine falciparum malaria autopsy cases from the Hospital for Tropical Diseases, Mahidol University, Bangkok, Thailand were divided into two groups that had had either cerebral malaria (CM) or non-cerebral malaria (NCM). We then studied significant pathological differences between these groups in order to investigate the correlation between parasitized erythrocyte (PRBC) sequestration in small blood vessels in the brain, heart, lungs and small intestines. We found that the percentage of PRBC sequestration in the organs which we studied was higher in the CM patients than in the NCM patients. The difference of PRBC sequestration among the organs of two groups was significant (P < 0.05). In the CM group, the average percentage of PRBC sequestration in the brain was significantly higher than in the heart, lungs and small intestines (P < 0.05). No statistically significant difference was found between PRBC sequestration in the brains, hearts, lungs and small intestines in the NCM group (P > 0.05). Our study indicates that severity of malaria in the CM patients depends on PRBC sequestration, especially in the brain. A combination of functional disturbances of the other organs, in addition to the cerebral pathology, may augment the severity of the disease.

Normal and immune mice were evaluated for their ability to resist infection to the rodent malaria parasite, Plasmodium yoelii, during pregnancy. Parasitemia levels were slightly higher and time-to-death shorter in the nonimmunized pregnant group infected with virulent parasites relative to virgin controls. Subinoculation experiments revealed that numerous virulent organisms were present in the placentas of unprotected gravida but were absent from the fetal livers of their conceptuses. It was also found that mice preimmunized with irradiated P. yoelii survived a usually lethal challenge infection during midgestation and delivered healthy newborns. Associated with this protection against transplacental spread of parasites was the additional key finding that placental macrophages were as effective as peritoneal exudate cells in phagocytosing parasite derived material in vitro. This murine malaria-pregnancy model should provide new insights on the various factors (virulence, immunogenicity) of microbial infections affecting the fetal-maternal relationship, as well as on the expression of immune effector mechanisms and immunoregulation, during the reproductive process.

An epidemiologic study of hyperendemic malaria in Arso PIR, a village in northeastern Irian Jaya (Indonesian New Guinea), revealed evidence suggesting suppression of gametocytemia independent of immune control of the asexual parasitemia. A total of 240 people, representing ages between 2 and 60 years, were followed by biweekly blood film examination for 16 weeks beginning in November 1987. Two distinct subpopulations were represented — 1) life-long residents of Irian Jaya, and 2) transmigrants from Java who arrived in Irian Jaya 20 months before the surveillance effort began. Twenty-five percent of blood films from natives and 31% from Javanese were positive for falciparum malaria; of these, the rate of gametocytemia was 21% for natives, and 42% for the Javanese transmigrants (P < 0.001). This difference could not be explained by differences in the frequency or grade of parasitemia, illness, or by known patterns of antimalarial consumption. Similarly, in Wor, a village near Arso PIR, the gametocyte rate for P. falciparum diminished from 83% to 25% in transmigrants from Java between their eleventh and twenty-fifth month of residence in Irian Jaya, a period during which the falciparum malaria rate remained stable between 30% and 50%. An immunofluorescent antibody test using whole, acetone-fixed gametocytes as substrate revealed correlation between antibody titer and protection from gametocytemia among the semi-immune natives of Arso PIR, but not among the Javanese. Specific immune suppression of gametocytes, independent of immune control of asexual parasites, can explain all of these observations.

Investigators studied 348 children age 0–10 years, living in a holoendemic area of Liberia, for parasitological, serological and clinical parameters.

The age-specific parasite rate increased towards the 7–10 year-old age group in which it was 86.8%. The geometrical mean parasite density decreased from the 3–4 year-old age group, in which fewer episodes of clinical malaria were observed.

Antibodies to crude Plasmodium falciparum parasite antigens were detected in all children. The (EENV)6 seropositive rate was a maximum of 67.9% in the 3–11 month-old age group. It declined to a minimum of 31.7% in the 5–6 years age group after which it increased slowly in the 7–10 years age group. Antibodies to the synthetic peptide (NANP)6 showed a steady seropositive rate after the age of 3 months, between 30.0% and 39.3% in all the age groups up to 10 years. No statistically significant correlation was found between seropositivity to (EENV)6 and malarial parasitemia. In contrast, a statistically significant positive correlation was found between seropositivity to (NANP)6 and parasite rates.

The antibody response for the individual child was transient to both Pf155/RESA, measured by immunofluorescence, and to (EENV)6 and (NANP)6, measured by ELISA, especially in the younger age groups of this study population.

Parasitological and clinical immunity developed before a stable antibody response to these defined malaria antigens was established. These antibodies may still contribute to the immune protection against malaria, but they were not reliable parameters for protective immunity in the population we studied.

The role of naturally acquired circumsporozoite (CS) antibodies in protection against falciparum and vivax malaria was evaluated in a group of Thai endemic villagers using a prospective cohort and a case-control study design. There was no evidence of protection by either the presence of positive CS antibody levels at the presumed time of sporozoite exposure or in individuals who persistently had measurable levels of the antibodies. The study defined levels of CS antibodies that were not protective in natural infection.

Between 1986 and 1988, epidemiologic studies were carried out in a small rural community in an Andean region of Ecuador, where cutaneous leishmaniasis is highly endemic. A total of 25 human cases, positive for Leishmania parasites by culture and/or smear, were examined. Fourteen of the cases were in infants less than one year of age, suggesting intradomiciliary transmission of the disease. Clinically, many of these cases were similar to descriptions of “uta,” a form of cutaneous leishmaniasis which occurs in Andean regions of Peru and is reportedly caused by L. peruviana. Of the 11 positive cultures obtained from human cases in the present study, eight were identified by molecular characterization as L. mexicana and three were identified as L. major-like. Two additional isolates of L. mexicana were also made from an infected dog and from a sand fly, Lutzomyia ayacuchensis, living in the region, thus implicating the latter species as possible reservoir and vector, respectively, of L. mexicana in this highland community. The significance and validity of recent isolates of L. major-like parasites from the New World are also discussed.

The histopathology of primary forepaw and metastatic lymph node, spleen, and liver lesions produced in golden hamsters infected with cutaneous leishmaniasis (CL) strains (LTB111 and LTB558) and mucocutaneous leishmaniasis (MCL) strains (LTB12 and LTB201) of Leishmania (Viannia) braziliensis isolated from patients residing in Tres Bracos, Bahia, Brazil is described. No pathological features providing clear differentiation of the CL and MCL strains were found. Although amastigotes were plentiful early in the development of primary forepaw lesions, they were either absent or could not be identified with certainty in sections of late stage lesions. Similarly, amastigotes were not found in histologic lesions at metastatic sites; however, leishmanial DNA was detected in both early and late stage forepaw lesions and metastatic lesions using Leishmania kinetoplast DNA and the gene coding for gp63 as hybridization probes. The DNA recovered from metastatic lesions was extracted from formalin-fixed paraffin-embedded tissues that had been stored at room temperature for prolonged periods.