The American Journal of Tropical Medicine and Hygiene - Volume 44, Issue 4, April 1991

Daily survivorship, duration of the gonotrophic cycle, absolute abundance and season-long relative abundance were estimated for Aedes melanimon in the Sacramento Valley of California in 1987 and 1988 using mark-release-recapture (MRR) techniques and by monitoring changes in the abundance and parity rate of the native population. One objective of these studies was to determine the extent to which A. melanimon was biologically capable of serving as a horizontal arbovirus vector. Daily survivorship was estimated to be 0.90 and 0.84 in MRR studies conducted in September 1987 and August 1988, 0.89 based on changes in the parity state and abundance of the native population in August 1988 and 0.82 using summer-long parity data in 1988. Gonotrophic cycle length (GCL) was estimated to be five days in three studies. Aedes melanimon densities were estimated to be approximately 1,000,000 and 15,000 females per hectare in September 1987 and August 1988 respectively. Parous A. melanimon females were collected on each sampling occasion from April to November 1988, suggesting that A. melanimon maintained a continuous presence in the study area throughout the summer.

The results of these studies suggest that A. melanimon has the potential to be an efficient horizontal vector of western equine encephalomyelitis (WEE), based on high adult survivorship, short GCL, high abundance and a continuous presence across the summer. This supports the concept of a WEE transmission cycle in the Sacramento Valley involving Ae. melanimon as an important vector. Aedes melanimon also can be an efficient horizontal vector of California encephalitis virus (CE), though the importance of horizontal transmission to the maintenance of CE virus is unclear.

The first epidemic of dengue in China associated with significant severe and fatal hemorrhagic disease which met the World Health Organization case definition occurred on Hainan Island in 1985–1986. The epidemic began in Zhan County in September 1985, spread throughout the coastal areas, and ultimately involved 13 counties and cities of the island in 1986. The mosquito vector was Aedes aegypti. The morbidity associated with dengue infection on Hainan Island was 1,913 per 100,000 residents, with a case fatality rate of 0.25%. Severe disease was more prevalent in the 10–29-year-old age group. Principal clinical features in laboratory-confirmed cases were fever, osteoarthralgia, hemorrhage and/or shock, and thrombocytopenia. Complications such as acute intravascular hemolysis, diffuse intravascular coagulation, hemoconcentration, pleural effusion, altered mentality, and pneumonia were also observed. One hundred twenty-five isolates of dengue 2 virus were recovered from acute-phase serum samples from 278 patients, and 5 strains of this same virus serotype were isolated from 5 pools of adult Ae. aegypti.

Since 1975, there has been an increase in the number of patients with tsutsugamushi disease in Japan, and marked antigenic heterogeneity has been found among newly isolated strains of Rickettsia tsutsugamushi. For antigenic analysis of these strains, we produced monoclonal antibodies against the Irie strain isolated in 1971, and the Hirano and Shimokoshi strains isolated in 1980. In all, 34 monoclonal antibodies were produced and their reactivities were determined by the immunofluorescent antibody test. The serological reactivity of the antibodies against these three strains and classic representative strains (Gilliam, Karp and Kato) showed varied reactive characteristics, i.e., serotype-specific, species-specific and intermediate reactivities. It was revealed that these strains are antigenically different from the classic ones. Moreover, by using the serotype-specific monoclonal antibodies, nine strains newly isolated in Miyazaki Prefecture were classified into the Irie and the Hirano types. The antigenicity of the Shimokoshi strain differed from those of the other strains used in this study. From these results, the strains of R. tsutsugamushi used in this study fell into six serotypes including the classic strains. SDS-PAGE and immunoblotting were performed to determine the molecular sizes of the antigenic polypeptides. The results revealed that the serotype-specific antigens belong to the 60-kDa class whereas the species-specific antigens belong to the 61-kDa, 60-kDa or 44-kDa class.

We studied Aotus lemurinus, Panamanian night monkeys, for susceptibility to Toxoplasma infection and for their capacity to develop immunity using either sufadiazine prophylaxis or the non-persistent ts-4 vaccine. The animals were highly susceptible to infection with a mouse pathogenic (T265) and a mouse nonpathogenic (T163) Toxoplasma isolate. A calculated single bradyzoite by mouth gave rise to infection which was fatal in nine to 12 days. Chemoprophylaxis with 60–300 of sulfadiazine mg per day for up to 40 days protected the animals; however this was followed by fatal reactivation of infection between 11 and 70 days after treatment was stopped. Vaccination was carried out in two or three doses subcutaneously. Challenge was performed in 26 animals using both Toxoplasma isolates. Five monkeys (19%) survived for over a year, 10 died after a prolonged illness, and 11 died as rapidly as the seven controls. Safety tests showed the vaccine to be nonpathogenic in 111 adults except for slight fever and local inflammation, although one of four juveniles died from disseminated infection. Vaccination of 25 pregnant monkeys was non-pathogenic; however two of 25 fetuses were aborted, one of which was infected and one newborn had microphthalmia, retinitis and a cataract; four of the offspring were not tested. When six lactating monkeys were vaccinated, Toxoplasma was not transmitted to the infants. The high susceptibility to Toxoplasma and the low immunizability was circumstantially attributed to absence of exposure and lack of selection by Toxoplasma of these arboreal monkeys even though about 50% of terrestrial animals from the same area were infected. Therefore, because they are apparently unselected by Toxoplasma, these monkeys proved to be a sensitive primate model for safety tests. They are however, unsuitable for evaluation of vaccine potency which was demonstrated in mice, hamsters and rabbits.

In a prospective study conducted in Mymensingh district of Bangladesh, 1, 273 patients were assessed for the presence of visceral leishmaniasis (VL). Sodium antimony gluconate (SAG) was successfully administered to 715 patients with parasitologically confirmed infection. In the remaining 558, although there was clinical indication of VL, Leishmania donovani parasites could not be demonstrated. Administration of SAG in this group was on the grounds of the prevailing symptoms, exclusion of malaria and a positive direct agglutination test (DAT). Significant improvements in the clinical and hematological parameters were observed in 547 (98%) of the unconfirmed VL cases. On the basis of the parasitological findings or positive response to specific anti-Leishmania chemotherapy, the sensitivity and specificity of the DAT were 99.6% and 97.7% respectively. The results supported the reliability of DAT for diagnosis of VL at levels below that of parasitological detection.

We tested the World Health Organization (WHO) recommended treatment for mucosal leishmaniasis in 16 Panamanians with disease due to Leishmania braziliensis panamensis. Disease was mild in this population because it was limited to the nasal mucosa and only one patient had septal perforation. The patients were administered 20 mg antimony (in the form of Pentostam) per kg intravenously each day for 28 days. Ten patients completed therapy and were cured at 12 month follow-up. Three patients completed therapy, healed their lesions, but relapsed at the six or 12 month follow-up. Three patients terminated therapy prematurely because of liver enzyme elevations in conjunction with either EKG abnormalities or musculoskeletel complaints; none of these patients were healed. This study indicates that in patients with mild mucosal leishmaniasis, the WHO regimen is curative in 77% patients who complete treatment and in 63% of all patients.

Animal models are needed for the study of cytoadherence in falciparum malaria. Red blood cell (RBC) rosette formation is one type of cytoadherence and appears to be associated with knob formation, endothelial cell adhesion and sequestration of Plasmodium-infected RBCs. Since Plasmodium coatneyi-infected RBCs develop knobs and sequester, we hypothesized that they also form rosettes. RBCs from P. coatneyi-infected rhesus monkeys (Macaca-mulatta) were collected, allowed to mature overnight in vitro and found to form rosettes as hypothesized. This observation adds to the known falciparum-like characteristics of P. coatneyi, and suggests that the Macaca mulatta-P. coatneyi model may be appropriate for pathophysiologic studies of cytoadherence.

Blood samples collected from five volunteers participating in a P. falciparum infectivity trial were examined to determine the efficacy of the acridine orange technique. Several lens configurations were tested for efficiency in the diagnosis of malaria using this system. There was no significant difference in the sensitivity for detecting positive specimens or number of parasites among three lens configurations: a 50 × long working distance objective (0.34mm) with either a 10 × ocular (total magnification 500 ×) or a 12.5 × ocular (625 ×) and a 750 × configuration using a 50 × objective with a shorter working distance (0.24mm). All three lens configurations were significantly better than the 1,000 × configuration using a commonly available 100 × oil immersion objective. The results achieved using this lens still exceeded the sensitivity of the thick blood film.

Renal specimens of squirrel monkeys (Saimiri sciureus boliviensis) were studied by light microscopy and immunohistochemistry to examine the pathologic changes during vaccine trials with four recombinant circumsporozoite (CS) proteins (rPvCS-1, rPvCS-2, rPvCS-3, NSl81V20) of Plasmodium vivax. The monkeys were vaccinated and later challenged with P. vivax sporozoites. Among the 33 posttrial biopsies, 17 had mild to moderate mesangial proliferation and nine had interstitial nephritis. Immunohistochemistry by the peroxidase-antiperoxidase (PAP) method revealed IgG deposits in only three of 24 specimens and failed to demonstrate C3 deposits and P. vivax antigens in their glomeruli. There was no relationship between the severity of nephropathy and intensity of parasitemia. The intensity of parasitemia was the same in the vaccinated and control groups. Vaccinated monkeys from the groups (rPvCS-1, rPvCs-2, rPvCS-3) had no differences in renal pathology from the unvaccinated controls, but one group vaccinated with NSl81V20 did not develop renal changes.

The capacity of Trypanosoma rangeli antigens to induce immune response in mice was analyzed and the course of the infection was studied in immunized animals challenged with virulent forms of T. cruzi. BALB/c mice were immunized with supernatant of disrupted epimastigotes of T. rangeli and with epimastigotes (EPI) of T. rangeli fixed with glutaraldehyde. Both of the antigens were emulsified with incomplete Freund's adjuvant (IFrAdj). All of the animals received T. cruzi Tulahuen antigens in the footpad and the skin reactivity was later studied. The mice that received EPI with or without IFrAdj showed significantly higher skin reactivity than controls, both in Arthus (3 hr) and delayed type hypersensitivity (24 hr) reactions. Furthermore, the mice immunized with T. rangeli developed antibodies against T. cruzi detectable through hemagglutination and immunofluorescence tests. When the animals were challenged with trypomastigotes of T. cruzi, only the groups immunized with EPI-IFrAdj had significantly lower parasitemias and greater survival against infection than controls. These results suggest that T. rangeli can induce humoral and cellular immune response against T. cruzi and attenuate the acute period of the infection produced by this parasite. This is the first time that partial resistance to T. cruzi in T. rangeli-immunized mice is reported. These findings may provide a useful tool for future studies directed at the immunoprevention of Chagas' disease.

This report is concerned with ten patients treated surgically for a splenic hydatidosis. Splenic echinococcosis represents 3.5% of abdominal hydatid cysts treated in our Service. When splenic hydatidosis was diagnosed, the spleen was the first and only localization of hydatid disease in three cases. One of these patients underwent surgery for a pulmonary cyst four years later. Splenic cysts were asymptomatic in six patients. The most frequent clinical sign of splenic hydatidosis was a painful mass in the left upper abdominal quadrant. Ultrasonography and axial computed tomography (axial C.T.) were the most useful diagnostic tools. The complications arising from splenic hydatidic cysts were infection, rupture in the abdominal cavity and fistulization to the colon. A splenectomy was performed in every case. There was no mortality and morbidity was principally related to the hepatic-associated hydatidosis. It is concluded that splenic involvement is a rare manifestation of hydatid disease but should be looked for in a systematic way in patients with this diagnosis.

In 19 children with hepatic fibrosis as the result of continued schistosomiasis mansoni and 20 children without hepatic fibrosis, the following studies were carried out: HLA antigen typing for 30 antigens, immune response of T lymphocytes to schistosome antigen by measuring DNA synthesis evidenced by 3H-thymidine uptake, and measurement of total OKT3+, OKT4+, and OKT8+ cells using monoclonal antibodies. Patients with hepatic fibrosis were mostly high responders in contrast with those without fibrosis. High immune response and susceptibility to post-schistosomal hepatic fibrosis were associated with a high frequency of A2 and B12 antigens and a lack of DR2 antigens, while low response was associated with the presence of the DR2 antigen. The T4+:T8+ ratio showed increased suppressor proportions in patients with low immune response and/or with no hepatic fibrosis. We suggest an immunogenetic susceptibility for post-schistosomal hepatic fibrosis, probably controlled by HLA-linked genes via the suppressor T cells.

Granulomatous hypersensitivity to parasite eggs of Schistosoma mansoni is an important factor in the development of morbidity in chronic schistosomiasis. It has been demonstrated previously that the chronic, well-tolerated, intestinal form of schistosomiasis is associated with the establishment and maintenance of a variety of immunoregulatory mechanisms. We have used an in vitro model of granuloma formation for the purpose of studying the regulation of granulomatous hypersensitivity to S. mansoni egg antigens, mediated by immune complexes (IC). Our results show that the peripheral blood mononuclear cells (PBMCs) from patients with active schistosome infections, when treated with sera from chronic schistosomiasis patients, were able to induce an inhibitory activity on in vitro granuloma formation. Significant modulation of the in vitro granuloma reaction remained after treatment of PBMCs with isolated IC or manufactured IC with soluble egg antigen (SEA) and purified IgG from pooled chronic schistosomiasis sera. In contrast to granuloma modulation stimulated with whole molecule IgG-SEA IC, the incubation of PBMCs with F(ab′)2 IgG-SEA IC did not induce any suppression of the granulomatous hypersensitivity to SEA. It appears in this model system that IC may inhibit the activity of granuloma formation by stimulating macrophages to release suppressive mediators. We have demonstrated this possibility by inhibition of prostaglandin activity using indomethacin. The addition of indomethacin to the granuloma culture significantly reduced in vitro granuloma modulation. These results demonstrate that circulating IC may regulate granulomatous hypersensitivity to S. mansoni eggs in patients with chronic intestinal schistosomiasis and do so by inducing macrophages to secrete prostaglandins.

Five hundred thirty six Sudanese schoolchildren with Schistosoma mansoni infection were treated at random with either 20 mg or 40mg/kg praziquantel. Seven months later 420 children could be reinvestigated by ultrasonography. Reduction of egg excretion and reversibility of sonographically-proven periportal fibrosis (PF) was not significantly different in the two groups. Schistosoma mansoni-induced PF grade II decreased from 22.9% to 6.7% and grade III from 5.2% to 1.6%. An increased prevalence of PF grade I, from 10% to 29.8% of the investigated patients, was observed. This increase was caused partly by a downshifting of patients who had PF II (n = 45) and PF III (n = 8) before therapy, but also by patients who developed PF I in the seven months after therapy (n = 56). The overall percentage of patients with PF before and after treatment was 38.1%. Of 420 children, 17.4% increased in their PF grade, 55% remained at the same level and 27.6% improved. Children younger than 11 years of age had a higher rate of complete reversibility than older ones. The percentage of patients with hepatomegaly decreased significantly (11.6% to 6.9%; p = 0.001). The rate of splenomegaly remained unchanged. It was concluded that within seven months therapy with praziquantel resulted in a considerable qualitative improvement of PF in Sudanese schoolchildren with S. mansoni infection.

Following envenomization by Echis carinatus sochureki, a professional snake handler developed a profound coagulopathy manifested by hemorrhage from the bite site, venipuncture sites and gums; coagulation testing revealed prothrombin and partial thromboplastin times greater than 150 seconds, a fibrinogen of 0 mg%, and marked elevation of fibrin degradation products. In addition, protein C antigen levels were undetectable. The coagulopathy was treated with cryoprecipitate; two different antivenoms were also administered with uncertain benefit. Subsequently, the properties of the venom and antivenoms were studied. Venom did not directly clot fibrinogen; however, venom concentrations as low as 0.2 µg/ml caused significant prothrombin activation. In addition, venom activated protein C in the absence of thrombomodulin, and this activity was inhibited by hirudin. The ability of four commercial antivenoms to neutralize the venom prothrombinase and hemorrhagic activity was measured. Three of the four antivenoms partially neutralized venom-induced prothrombin activation. Extreme differences in efficacy were found among the four antivenoms in neutralizing venom hemorrhagic activity in mice. This case illustrates the difficulty in managing the complex coagulopathy that can result from exotic snake envenomization, and identifies a new coagulant property of Echis carinatus venom (protein C activation).

Dr. Chana should be congratulated on writing a particularly interesting and useful book. Although many people may not be primarily concerned with the delivery of eye care and so many of the specifics of his book may not be relevant to them, all those involved in health care delivery or programmatic development will find this book both fascinating and informative. Dr. Chana has collected the material developed for the National Eye Care Program of Zimbabwe by the Ministry of Health and the Norwegian Association of the Blind and Partially-Sighted (NABP).

This manual has useful chapters covering topics such as the development of a country profile, bilateral agreements, inter-agency collaboration, manpower development, management and evaluation, and the role of women's groups. These chapters are illustrated with the material and experiences of the Eye Care Program in Zimbabwe. They provide a model that could be used in a generic way for any program in any country, but especially in Africa, and demonstrate the underlying and general principles of development.