The American Journal of Tropical Medicine and Hygiene - Volume 43, Issue 4, October 1990

The offices of McWilson Warren, the incoming Editor of The American Journal of Tropical Medicine and Hygiene, are located at 3088 Briarcliff Road NE, Suite A-1, Atlanta, GA 30329. All new manuscripts should be sent to him at that address. The Baltimore office of the JOURNAL will continue to be active for several months. Manuscripts currently under review and any correspondence pertaining to them should be sent to the address (Baltimore or Atlanta) indicated in the documents.

Anopheline survivorship, vectorial capacity, and mosquito infection probability estimates from mosquito infection rates were determined 4 times in 1 year in a Papua New Guinea village. Estimates of survivorship over the length of the extrinsic incubation period differed significantly during the year. However, survivorship per feeding cycle, individual mosquito vectorial capacity, and mosquito infection probability did not vary significantly. Estimates of these parameters were then compared to estimates of survivorship, individual vectorial capacity, and mosquito infection probability in mosquito populations in other villages in the study area. Since survivorship per feeding cycle did not vary significantly among the mosquito populations in these villages, changes in malaria transmission potential can be better gauged from estimates of survivorship over the length of the extrinsic incubation period. However, as measurements of relative inoculation rates are easier to perform and have been related to parasite prevalences in children in this area, estimates of inoculation rates are a preferred option for estimating malaria transmission in the Madang area of Papua New Guinea.

Four size classes of Anopheles dirus were reared from different larval densities. Higher densities produced smaller adults with lower survivorship. Larger females took larger bloodmeals by artificial feeding with cultured Plasmodium falciparum and developed significantly more oocysts.

Uninfected erythrocytes bind spontaneously to those infected with certain strains of Plasmodium falciparum. This is known as spontaneous erythrocyte rosetting. We have studied the occurrence and frequency of rosetting in 75 fresh patient isolates and have identified rosetting strains from Africa, South America, and Asia. Rosetting was present in 49% of the isolates tested; the frequency of rosetting red blood cells (RBC) in individual isolates was 0–75% when scored during the first cycle of in vitro growth. Rosetting antibodies were found in 15 out of 73 (21%) Liberian sera as measured by disruption of rosettes in vitro. However, antibodies able to inhibit CD36 dependent cytoadherence of P. falciparum-infected RBC were not detected in these sera. Erythrocyte rosetting is a geographically widespread phenomenon. Rosetting antibodies seem to be induced by natural infection and the molecular mechanism of rosette formation seems distinct from that of endothelial cytoadherence.

During the development of a synthetic vaccine for human use against the asexual blood stages of Plasmodium falciparum, monkey trials were performed to assess safety, immunogenicity, and protectivity. We determined the minimal infective dose of the P. falciparum FVO strain, the kinetics of the immune response induced by vaccination with the synthetic peptide mixture (S7 + S12 + S17) or the synthetic hybrid polymeric protein SPf66, and the induction of protective immunity against the experimental challenge with 2 P. falciparum strains. A clear boosting effect was observed, determined by the increased antibody titers against synthetic peptides S7, S12, S17, and SPf66, and by improvement in the protective immune response against the challenge. These studies suggest that either the peptide mixture or the synthetic hybrid polymeric protein are excellent choices for the development of a vaccine against P. falciparum.

A mixture of 3 synthetic peptides (35.1, 55.1, and 83.1) corresponding to portions of the 35 kDa, 55 kDa, and 83 kDa proteins from the asexual blood stages of Plasmodium falciparum and a polymer of a synthetic peptide incorporating the 3 individual peptides (SPf66) were tested as candidate malaria vaccine antigens in Aotus nancymai. Monkeys were immunized with combinations of the 3 peptides from 2 separate sources (Centers for Disease Control [CDC], Atlanta, GA or Colombia) or with the synthetic polymer. Animals immunized with a combination of the 3 peptides from CDC had higher antibody titers to the 35.1 and 55.1 peptides than to the 83.1 peptide. Monkeys immunized with a combination of the 3 peptides produced in Colombia developed higher levels of antibody to the 55.1 than to the 83.1 and 35.1 peptides. Animals immunized with the polymer produced detectable antibodies to the 55.1 peptide alone. Following challenge with P. falciparum, no differences were observed between the 3 vaccine groups and 2 control groups with respect to the number of animals with parasitemias ≥10%. The inconsistency of serologic response to all 3 peptides in these animals contrasted with previous trials performed in Colombia where the monkeys developed high antibody titers against the 3 peptides and were protected against the experimental infection.

A genetic analysis using enzyme data of 72 Leishmania mexicana isolated from hosts in Texas, Latin America, and the Caribbean is presented. All isolates from each country were combined and considered as local populations. Allomorph (allele determined by electrophoresis) frequencies for 20 enzyme (loci) were calculated and 7 populations (Texas, Mexico, Belize, Guatemala, Ecuador [EC], Venezuela, and the Dominican Republic [DR]) were compared pairwise in the statistic of genetic identity (I) (level of genetic similarity). All populations were found to be genetically similar with a mean I value for all comparisons of 0.890 ± 0.067. When DR was included as one of the pair compared, Ī = 0.811 ± 0.034. Among comparisons that include EC (excluding EC vs. DR), Ī = 0.875 ± 0.026. The mean I for the other comparisons was >0.9. The data indicate that the DR population is divergent enough from the others that it can be considered at the subspecies/incipient species level of evolutionary divergence; the EC population is, to a lesser extent, distinct from the others, and the other 5 represent geographic populations of 1 widely distributed species. A diagrammatic representation of the allomorphs among the 72 isolates is included. There were some allomorph/geographical (or local) population relationships noted.

A 65 kDa protein (Bb65) has been identified as one of the major specific antigens of Bartonella bacilliformis, the causative agent of bartonellosis which is a bacterial infectious disease of inhabitants of the Andes. The gene encoding this antigen (7B2) was isolated from an expression library made directly from randomly generated fragments of B. bacilliformis genomic DNA using Bartonella antibodies raised in rabbits and sera of bartonellosis patients. The Bartonella 7B2 gene was expressed in Escherichia coli and the recombinant Bb65 protein was purified by column chromatography. Using polyclonal antibodies raised in rabbits, the antigen was shown to be present in all of 13 B. bacilliformis isolates from different Peruvian regions. Immune electron microscopy demonstrated the probable cytoplasmatic localization of Bb65. When applied to enzyme immunoassays, Bb65 sensitively and specifically bound to IgG antibody of sera of bartonellosis patients, convalescents, and immunes from various Peruvian regions. IgM antibody was not recognized by Bb65, neither was IgG antibody circulating during the first 2 weeks of illness. The amino-terminal amino acid sequence of Bb65 was 53% homologous to the 65 kDa heat shock protein of Mycobacterium tuberculosis.

The efficiency of ultrasonography (US) for the diagnosis and clinical characterization of onchocerciasis was evaluated. US was performed on 120 probands in Liberia. Ninety-two patients had generalized onchocerciasis, 21 patients suffered from the chronic hyperreactive form of onchocerciasis (sowda), and 7 probands served as controls. Patients were examined by US with linear (7.5 MHz and 5 MHz) and sector (3.5 MHz) scanners. US results were evaluated by examination of extirpated nodules. The US structure of nodules revealed a typical pattern consisting of a homogeneous echogenicity with small echodense particles and a lateral acoustic shadow, and differentiation from lymph nodes, lipoma, or fibroma was achieved. Within the onchocercomata, calcifications or fluid were identified. Regarding the estimation of the worm burden, it is important to note that in 24 patients, additional nodules not previously palpated were found by US. Also, the number of worm centers in palpable conglomerate nodules was determined more exactly by US than by palpation. In 4 of 16 sowda patients, impalpable nodules were found by US. In 13 patients with positive microfilaria counts, no nodules could be detected. The highly characteristic ultrasonographical pattern of onchocercomata may serve as a basis for further US investigations in onchocerciasis.

A case of South American blastomycosis began with an oropharyngeal lesion which was followed by a granulomatous uveitis. The patient was treated with Amphotericin B and showed a clinical regression. Four months later, he developed a right 3rd cranial nerve palsy, aggravating the clinical aspect with a severe generalized involvement of the central nervous system and death. Necropsy showed blastomycotic meningoencephalitis.

Yersinia pestis produces a glycoprotein capsule, the biosynthesis of which appears to be temperature dependent. The fraction I (F1) component of this capsule is specific to Y. pestis and the detection of F1 antibodies is the basis for several serological tests. We report the cloning of the F1 gene and its expression in Escherichia coli using the phagemid vector λZAPII and a F1-specific monoclonal antibody. The recombinant F1 antigen had a molecular weight of 17 kDa, which proved to be identical to that of the F1 antigen produced by Y. pestis. The recombinant cells produced F1 antigen at 37°C but only minimal amounts at 27°C, suggesting that the genetic features affected by temperature in Y. pestis may be operating in the E. coli clone. It is not known if their similar molecular weights reflect the glycosylated nature of both proteins. F1 antigen purified from the E. coli recombinant induced a protective immune response in BALB/c mice challenged with up to 105 virulent Y. pestis. The resistance of immunized mice to plague infection correlated with high titers of F1 antibody. The cloned gene expresses an immunogenically competent F1 antigen suitable for use in plague serodiagnostics and vaccine development.

High-level gentamicin resistance (minimum inhibitory concentration of ≥2,000 mcg/ml) in Enterococcus faecalis has not previously been reported in Africa to our knowledge. Eight of 28 (29%) rectal swab specimens obtained from hospitalized patients in Zimbabwe had gentamicin resistant enterococci. Previous exposure to penicillins or aminoglycosides were risk factors for colonization with these organisms. This study documents the presence of high-level gentamicin resistant enterococci in Africa and suggests that penicillin or aminoglycoside usage may select for gentamicin resistant enterococcal plasmids in Africa.

We report the ultrastructure of a rickettsia-like microorganism in a colonized population of the cat flea Ctenocephalides felis (Bouché). The microorganism occurs principally in the cytoplasm of midgut cells, but similar microorganisms were detected in the tracheal matrix, muscle, hypodermis, ovaries, and the epithelial sheath of the testes. The microorganism has a well-defined cell membrane consistent with rickettsia and measures 0.25–0.45 µm in diameter with lengths up to 1.5 µm. It was observed repeatedly in fleas of 1 laboratory colony, including newly emerged non-bloodfed specimens, but not in specimens from several other sources.

Preliminary studies found that 9% of Guaymi Indians from Bocas del Toro province have antibody to human T cell lymphotropic virus (HTLV-I/II). The present study enrolled 317 (21% of the population) Guaymi Indians from Changuinola, the capital of Bocas del Toro province and 333 (70% of the population) from Canquintu, an isolated rural village. Demographic information and family relationships were ascertained and subjects were screened for neurologic diseases. Serum specimens were screened by an enzyme-linked immunosorbent assay for HTLV-I/II antibody and positives were confirmed according to U.S. Public Health Service criteria. Twenty-five (8%) Guaymi residing in Changuinola and 7 (2.1%) from Canquintu were confirmed seropositive. In Changuinola, antibody was virtually limited to residents ≥15 years of age (24 [16%] of 153) and rates were slightly higher in males than in females; in Canquintu, antibody rates did not increase significantly with age and appeared higher in females than in males. In Changuinola, there was no evidence for household clustering of infection. In contrast, HTLV antibody among Canquintu residents clustered significantly by household. HTLV-associated neurologic disease was not detected in either population. The atypical seroepidemiology observed in both locations might be explained if the virus endemic to the Guaymi differed from HTLV-I previously described in the Caribbean basin and Japan.

The persistence of arboviruses was studied from 1983 to 1988 in mixed agriculture, marsh, riparian, and foothill habitats in Kern County, CA. Western equine encephalomyelitis (WEE) virus was isolated frequently during 1983 from Culex tarsalis and Aedes melanimon and was detected by the seroconversion of sentinel chickens. WEE virus then disappeared, even though vector competence studies during 1984–1986 showed that Cx. tarsalis was able to transmit WEE virus. St. Louis encephalitis (SLE) virus was detected sporadically in 3 of the 6 years of the study by isolation from Cx. tarsalis and/or by sentinel chicken seroconversion. When mosquito pools were screened for virus in suckling mice, Turlock (TUR) and Hart Park (HP) viruses were isolated from Cx. tarsalis during each summer. Vertical transmission of HP was indicated by the isolation of virus from a pool of male Cx. tarsalis. California encephalitis (CE) virus was isolated repeatedly from host-seeking Ae. melanimon females, males, and adults reared from field-collected immatures, verifying vertical transmission in nature. Horizontal transmission of CE virus among both jackrabbits (Lepus californicus) and desert cottontails (Sylvilagus auduboni) appeared to amplify Ae. melanimon infection rates during the summer of 1985, but elevated herd immunity depressed infection rates during 1986. Thus, CE, HP, and TUR viruses persisted in Kern County, while WEE virus appeared to become extinct and required reintroduction. The sporadic occurrence of SLE virus activity remains unexplained, but its persistence may require both vertical transmission and reintroduction.