The American Journal of Tropical Medicine and Hygiene - Volume 40, Issue 2, 1989

The human malaria parasite, P. falciparum, exhibits cytoadherence properties whereby infected erythrocytes containing mature parasite stages bind to endothelial cells both in vivo and in vitro. Another property of cytoadherence, “rosetting,” or the binding of uninfected erythrocytes around an infected erythrocyte, has been demonstrated with a simian malaria parasite P. fragile which is sequestered in vivo in its natural host, Macaca sinica. In the present study we demonstrate that rosetting occurs in P. falciparum. Rosetting in P. falciparum is abolished by protease treatment and reappears on further parasite growth indicating that, as in P. fragile, it is mediated by parasite induced molecules which are protein in nature. P. vivax and P. cynomolgi, which are not sequestered in the host, did not exhibit rosetting. Rosetting thus appears to be a specific property of cytoadherence in malaria parasites.

We investigated whether thrombospondin plays a role in the binding of Plasmodium falciparum parasitized erythrocytes to C32 melanoma cells. Twelve patient isolates bound variably to melanoma cells, with good correlation between the degree of binding to cells and binding to thrombospondin. With a synchronous preparation of asexual parasites, acquisition of the capacity to bind to thrombospondin occurred at the same parasite stage as binding to melanoma cells. Development of parasites to trophozoites and schizonts correlated with binding of parasitized erythrocytes to thrombospondin and melanoma cells. The infected erythrocyte receptor for thrombospondin was destroyed by mild trypsinization, as was the receptor for melanoma cells. Although these results suggest similarity in the melanoma cell receptor and thrombospondin receptor for infected cells, other results showed that thrombospondin cannot alone be the melanoma cell receptor. Binding to other melanoma cell lines did not correlate with thrombospondin secretion: the RPMI 8252 and G361 cell lines bound few or no infected cells, yet secreted 50–100% as much thrombospondin as C32 cells. Iodinated thrombospondin bound in similar amounts to C32 cells and to noncytoadherent C361 melanoma cells. Binding and nonbinding melanoma cells did not differ in quantity of surface thrombospondin by radioimmunoassay. Thus, although purified, immobilized, thrombospondin binds parasitized erythrocytes, expression of thrombospondin alone on melanoma cells is not sufficient to mediate adherence.

Plasmodium falciparum infected Anopheles stephensi, taken from a group of mosquitoes which had been used to challenge recipients of (NANP)3-TT vaccine, were tested for P. falciparum sporozoite content by an immunoradiometric assay. Seventy-six percent were infected with mean and median sporozoite equivalents per mosquito of 220,994 and 217,398, respectively (SD = 54,911). This sporozoite density is greater than that usually found in the field. These data suggest that this challenge for evaluating P. falciparum sporozoite vaccines is a demanding test of immunity.

We used colloidal gold probes and post-embedding immunoelectron microscopy to localize circumsporozoite (CS) antigen in 5- and 8-day-old in vitro cultures of Plasmodium cynomologi exoerythrocytic (EE) schizonts. Both small uninucleated and large multinucleated EE schizonts were found in 5-day-old cultures. A mouse monoclonal antibody to the repeat region of the P. cynomolgi CS protein densely labeled the plasma membrane and surface of 5-day-old EE schizonts as well as the surrounding parasitophorous vacuole membrane and space. Density of labeling decreased significantly as EE schizonts increased in size and maturity. Labeling of large, multinucleated 5-day-old schizonts was sparse and limited to the surface of EE schizonts and to small patches of electron dense material which were attached to the inner surface of the parasitophorous vacuole membrane. Mature 8-day-old EE schizonts with developing merozoites had little detectable labeling. CS antigen was not associated with internal structures within developing schizonts. Labeling was not observed in the host cell cytoplasm or on the surface of infected hepatocytes. These findings indicate that epitopes associated with the repeat region of the P. cynomologi circumsporozoite protein are sequestered within infected host cells during EE development.

In malaria endemic areas, pregnancy predisposes previously immune women to clinical and subclinical malaria infection. While parameters of humoral immunity do not seem to be affected to pregnancy, suppression of cellular immunity has been demonstrated for a number of antigens. In this study of women from a rural area of the Gambia where falciparum malaria is holoendemic, we show that lymphoproliferative responses to Plasmodium falciparum antigens are depressed in pregnant women compared to parity matched non-pregnant women, and that this effect is particularly marked in primigravidae. The data also indicate that malaria antigen induced γ-interferon production may be depressed in pregnant women. There was no significant difference in antimalarial antibody titers between the 2 groups.

Phospholipase A2 (PLA2) plays an important pathogenic role in infections caused by several microorganisms and has been implicated in host cell invasion. The mechanism of host cell penetration by the intracellular protozoan Toxoplasma gondii involves several steps; we have investigated the role of PLA2 in cellular invasion by the tachyzoite stage of this parasite. We assayed T. gondii invasion of human fibroblast monolayers by measurement of the selective incorporation of 3H-uracil into growing intracellular parasites. Exogenous PLA2 from snake venom (Naja naja) increased the penetration of fibroblasts by T. gondii, while horse antiserum to Naja hannah venom inhibited penetration. An irreversible PLA2 inhibitor, p-bromophenacyl bromide, blocked penetration without metabolically disabling the parasite. When host fibroblasts were preincubated with this drug, penetration was not affected, supporting a role for parasite rather than host cell PLA2 in the penetration process. Another PLA2 inhibitor, nordihydroguaiaretic acid, also inhibited penetration. We assayed extracellular T. gondii tachyzoites, purified from host cell debris, for PLA2 activity by radiometric detection of fatty acid release from labeled Escherichia coli membranes. Sonically disrupted parasites contained a low level of calciumdependent PLA2 with maximum activity at pH 8.5–9.0. These experiments suggest that a phospholipase is implicated in T. gondii host cell invasion.

In this report we summarize 5 cases of kala azar with disseminated dermal leishmaniasis. All had fever, hepatosplenomegaly, and disseminated skin lesions on admission. Maculopapular, pustular, and maculonodular eruptions were present, located mainly on the face and extremities. Innumerable amastigotes were demonstrated in the bone marrow and in the skin biopsies. All patients responded to Glucantime therapy.

Six strains of Leishmania isolated from wild mammals and humans on the Pacific Coast of Ecuador were identified by isoenzyme electrophoresis and by their reactivity patterns to a cross-panel of specific monoclonal antibodies using a radioimmune binding assay. Single isolates from Sciurus vulgaris. Potos flavus, and Tamandua tetradactyla were identified as Leishmania amazonensis. Three other strains, isolated from cutaneous lesions of humans, were identified as Leishmania panamensis.

Promastigotes of Leishmania mexicana amazonensis WR 669 clone 4 were made resistant to antimony in the form of Pentostam (sodium stibogluconate) by exposure to media containing increasing concentrations of Sb. The dose of Sb expected to kill 50% of promastigotes and amastigotes of the parent sensitive clone (WR 669) and the resistant clone (WR 669R) was determined by exposure of suspensions in physiologic salt solution for 3 hr. The approximate Ed50s in µg Sb/ml were: 10,000 for WR 669R promastigotes; 7,000 for WR 669R amastigotes; 200 for WR 669 promastigotes; and 150 for WR 669 amastigotes. Thus, Sb resistance and Sb sensitivity expressed by promastigote clones are also expressed by their respective amastigotes. Studies with 125Sb-Pentostam showed that WR 669R amastigote resistance was not due to altered Sb uptake over 1 hr. When amastigotes pretreated with Pentostam were incubated with 14C labeled metabolic precursors, susceptibility to Sb was correlated with inhibition of glycolytic enzymes and of fatty acid beta-oxidation.

Specific human IgG antibodies bound to a Trypanosoma cruzi envelope were internalized by antigen receptor-mediated endocytosis. Ferritin conjugated antibodies and horseradish peroxidase (HRP) conjugated IgG were found inside parasite cytoplasmic vesicles. Nonspecific IgG that did not bind to the external membrane was not internalized by the parasite. The ratio of 3H-protein A labeled: specific IgG internalization by parasites in the exponential growth phase (95% epimastigotes) was much smaller than that of parasites in the late stationary growth phase (38% trypomastigotes). Antibodies bound to the latter parasite forms almost disappeared from their outer membranes after 12 hr incubation at 27°C. Results of experiments in which membrane bound antibodies were removed by an excess of pronase showed that only small amounts of radiolabeled IgG were found inside the parasites. The fate of immunoglobulins that vanished from external membrane receptors and did not accumulate inside the cells was explained by experiments in which the supernants of IgG-3H-protein A labeled parasites were precipitated with trichloroacetic acid (TCA). In these, membrane-bound antibodies were taken in and degraded by the parasites as increased amounts of free radiolabel appeared in the supernatants as functions of incubation time and parasite stage.

The biologically active sulfidopeptide leukotriene, leukotriene C4, is formed by the enzymatic action of leukotriene C4 synthase, which conjugates glutathione with leukotriene A4. We have found that a filarial glutathione S-transferase can function as a leukotriene C4 synthase. Glutathione S-transferase was purified from the cytosol of adult Dirofilaria immitis by glutathione-agarose affinity chromatography and was reacted with 25 µM leukotriene A4 methyl ester and 10 mM glutathione. The filarial enzyme catalyzed the formation of leukotriene C4 methyl ester, as shown by reverse phase high pressure liquid chromatographic analyses. The finding that filarial glutathione S-transferase can function as a leukotriene C4 synthase provides a mechanism whereby filarial parasites could form lipoxygenase pathway derived sulfidopeptide leukotrienes.

The association between glomerular disease and hepatosplenic schistosomiasis is well documented in reports from South America. During the present hospital investigation in Sudan, 58 patients admitted for intercurrent complications of advanced hepatosplenic schistosomiasis were studied. The patients, median age 35 years, had no concurrent Schistosoma haematobium infection. Diagnostic criteria included an enlarged spleen (n = 58), at least 1 episode of hematemesis (n = 55) and/or melena (n = 36), endoscopical demonstration of gastroesophageal varices (29/29 studied), ultrasonographical imaging of hepatic periportal fibrosis (18/18 studied), and intraoperative liver biopsy with characteristic histological findings (11/16 biopsied). Serum creatinine, urea, electrolytes, cholesterol, total protein, and electrophoresis were within normal limits. Median urinary protein/creatinine ratio was 0.06 and thereby not significantly different from European reference values. Only 1 patient had proteinuria of 1.7 g/l. Minimal hematuria was found in 5 patients. Ten kidney biopsies were taken intraoperatively during a portal decompression procedure (Hassab operation). Light, immunofluorescence, and electron microscopy produced no evidence of glomerulonephritis. These findings indicate that S. mansoni induced nephrotic syndrome may be less frequent in Sudan than in South America. Renal involvement due to S. mansoni infection may therefore encompass geographical variances.

Peritoneal exudate cells from mice infected with Schistosoma mansoni (S-PEC) can kill a small proportion of schistosomula in vitro in the presence of immune serum. S-PEC produce a low level of respiratory burst. However, schistosomula mortality in their presence is not reduced when exogenous antioxidants are added, suggesting that with S-PEC, oxidative killing may not be important. Hydrogen peroxide (H2O2) and superoxide production by S-PEC, and cells from Bacillus Calmette-Guerin (BCG) and thioglycollate (THGL) injected mice, nonspecifically stimulated with opsonized zymosan, were measured. Levels of H2O2 produced by S-PEC were significantly lower than BCG or THGL PEC, and were below the threshold for schistosomula killing. This correlated with lower levels of cell-mediated killing of schistosomula in vitro by S-PEC than by BCG-PEC. Superoxide levels, however, were similar between the 3 cell populations. It therefore appears that the efficiency of PEC to kill schistosomules in vitro correlates with H2O2 rather than superoxide levels. It was found that there was a sharp concentration threshold in H2O2 mediated killing of schistosomula. A depression in the levels of H2O2 produced may be a mechanism by which the parasite can partially evade the host immune system.

Capillaria philippinensis eggs, larvae, and adults were identified in the stool of a 41-year-old female physician from Cairo, Egypt, who had never traveled abroad. She had eaten local and imported fish. She suffered from borborygmi, abdominal pain, severe diarrhea, vomiting, and loss of weight for >3 months. Treatment with Flubendazole (R17889-Janssen) 200 mg twice daily for 30 days resulted in clinical and parasitological cure.

The shell vial technique for isolation of cytomegalovirus was adapted to detect Rickettsia conorii in blood culture using human fibroblast monolayers. The inoculation was performed with low speed centrifugation and the rickettsiae demonstrated by immunofluorescence 24–120 hr after inoculation. R. conorii was identified in 11 of 13 patients with Mediterranean spotted fever in 48–72 hr.

To determine the prevalence of and risk factors for hepatitis B infection in rural Sudan, 2 villages in the Gezira were surveyed. There were 851 subjects (age 1–89 years; mean age 24.6 years) of equal sex distribution, 408 from Khalawaat and 443 from Saleim. HBsAg was found in 18.7%, and seropositivity for any hepatitis marker (HBsAg, anti-HBs, or anti-HBc) was found in 63.9%. The prevalence of HBsAg was highest in subjects <5 years of age (32.3%). Seropositivity for any hepatitis marker increased from 48.4% in subjects <5 years to 88.5% in persons ≥50 years of age. HBeAg was present in 70% of HBsAg-positive women of childbearing age. Residence in Khalawaat and parenteral therapy for malaria were found to be independent risk factors for HBsAg-positivity. Age, residence in Khalawaat, crowding, and having had a tattoo were predictive of seropositivity for any hepatitis marker. The reason for increased markers of hepatitis B in Khalawaat compared to Saleim was not apparent.

Larval Hyalomma truncatum ticks were infected with Crimean-Congo hemorrhagic fever (CCHF) virus by allowing them to engorge on viremic newborn mice. The overall tick infection rate was 4.4% (24/542). Virus was detected in specimens for ≥160 days postinfection. Transstadial transmission to the adult tick stage was observed and horizontal transmission to a mammalian host was demonstrated. Horizontal transmission of CCHF virus to uninfected adult ticks occurred while feeding with transstadially infected ticks on the same host. No evidence of transovarial virus transmission from infected female ticks to their 1st generation progeny was observed.

A novel virus-like infectious agent (VLIA), obtained by direct transfection of DNA from Kaposi's sarcoma of a patient with acquired immune deficiency syndrome (AIDS), was transmissible from culture to culture by cell-free filtrate. VLIA contained an outer limiting membrane and had a buoyant density of 1.17–1.20 g/ml in a sucrose gradient. The DNA genome of VLIA was estimated to be >150 kilobase (kb) pairs and carried repetitive sequences. An 8.6 kb pair cloned probe (psb-8.6) and a 2.2 kb pair cloned probe (psb-2.2) of VLIA detected specific sequences in DNA of VLIA infected cells, but not in DNA of uninfected NIH/3T3 cells. By Southern blot hybridization analysis, VLIA was distinct from all known members of human herpes virus, from vaccinia virus, monkey herpes virus saimiri (HVS), and mouse cytomegalovirus (MCMV). Using synthetic primers with the VLIA specific DNA sequences and the polymerase chain reaction (PCR) method, we detected VLIA sequences in DNA isolated from 7 out of 10 patients with AIDS. VLIA infection was identified in spleen, liver, brain, lymph node, Kaposi's sarcoma tissues, or peripheral blood mononuclear cells from these patients, but not in 5 different organs and a tumor from 5 subjects without AIDS. Antiserum raised against VLIA in rabbit positively immunostained brain and lymph node tissues from these AIDS patients.