Circumsporozoite proteins of human malaria parasites Plasmodium falciparum and Plasmodium vivax.

Monoclonal antibodies were raised against sporozoites of two species of malaria parasites, Plasmodium falciparum and Plasmodium vivax. The antibodies reacted with polypeptides (circumsporozoite proteins) that are uniformly distributed over the entire surface of sporozoites, as shown by indirect immunofluorescence and by the circumsporozoite precipitin reaction. The epitopes recognized by the monoclonal antibodies were expressed on sporozoites from different geographical isolates of the homologous species but were not detected on sporozoites of heterologous species nor on blood forms of the parasite. The monoclonal antibody to P. falciparum specifically immunoprecipitated two polypeptides of apparent 67,000 mol wt (Pf67) and 58,000 mol wt (Pf58) from extracts of [35S]methionine-labeled P. falciparum sporozoites. Similarly, the anti-P. vivax monoclonal immunoprecipitated two proteins of 51,000 mol wt (Pv51) and 45,000 mol wt (Pv45) from extracts of metabolically labeled P. vivax sporozoites. The extracts were also reacted with the serum of human volunteers successfully vaccinated with sporozoites of either P. vivax or P. falciparum. The patterns of immunoprecipitation were almost identical to those obtained with the corresponding monoclonal antibodies. The circumsporozoite proteins of P. falciparum and P. vivax play a role in immune protection. Incubation of the appropriate monoclonal antibody with viable sporozoites of the homologous species significantly reduced parasite infectivity, as determined by sporozoite neutralization assays carried out in splenectomized chimpanzees.

Antibodies against malaria sporozoites in patients with acute uncomplicated malaria and patients with cerebral malaria.

Serum samples from 95 patients with acute uncomplicated falciparum malaria (AM) and 95 patients with cerebral malaria (CM) were tested by the indirect immunofluorescent assay (IFA) for IgG and IgM antibodies against Plasmodium falciparum and P. vivax sporozoites. Forty-six (48%) CM patients were positive for antibodies against P. falciparum sporozoites whereas only 23 (24%) were positive for antibodies against P. vivax sporozoites (P less than 0.002). A similar result was obtained in AM patients. However, CM patients had significantly lower mean IgG anti-sporozoite titer for P. falciparum than did AM patients (P less than 0.05), especially when only anti-sporozoite antibody-positive CM and AM patients were compared (P less than 0.0005), suggesting that CM patients had relatively less exposure and were probably less immune to malaria than were AM patients. The persistence of anti-sporozoite antibodies also was investigated in paired sera taken 63 days apart from 108 patients with acute falciparum malaria. There were significant decreases in the mean antibody titers in the follow-up sera during the period of stay in the malaria-free area. It was proposed that determination of anti-sporozoite antibody be made as a substitute for, or in addition to, anti-blood stage antibody for seroepidemiological study of malaria, especially in the monitoring of the success of the malaria control program.

Preliminary field trial of a radioimmunoassay for the diagnosis of malaria.

A radioimmunoassay (RIA) has been developed for the detection of Plasmodium falciparum in infected blood. The assay is based on the ability of solubilized, infected red blood cells (RBC) (P. falciparum "antigen") to combine with anti-P. falciparum antibodies and thus prevent the subsequent interaction of the latter with "antigen"-coated microtiter plates. A preliminary trial was carried out in Thailand to determine the usefulness of the RIA for the immunodiagnosis of malaria. Blood samples from malarious and non-malarious patients were examined both by standard microscopy and by RIA. Efficient solubilization of the parasites proved to be a major requirement for the successful performance of the RIA. Sonication or freezing and thawing, which were perfectly satisfactory for the solubilization of cultured, infected RBC, were found to be totally inadequate when applied to RBC taken from patients. However, parasites in RBC from patients could be solubilized efficiently by treatment with detergents (e.g., NP40, Triton X-100, etc.). Of the 108 blood samples tested, 23 were found positive for falciparum parasitemia by microscopy and 39 by RIA. One sample from a patient with patent falciparum parasitemia and three with patent vivax parasitemia were negative by RIA. Ten of the samples positive only by RIA belonged to patients with recent malarial infection, as shown by microscopy. Thus, the RIA detected almost all of the patients with microscopic evidence of falciparum malaria. The proportion of false positives in the RIA test was low.

Plasmodicidal effect of desferrioxamine B in human vivax or falciparum malaria from Thailand.

Desferrioxamine B (DFO, Desferal), an iron chelator, was earlier shown to be active against Plasmodium falciparum in vitro and in vivo. The present open pilot study served to assess its clinical tolerability and efficacy in human malaria under hospital conditions. Continuous intravenous DFO was administered to 28 Thai males at a dose of 100 mg/kg over 24 h for 3 consecutive days. No other antimalarial therapy was administered unless recrudescence had occurred. The first 14 patients had symptomatic Plasmodium vivax (P.v.) malaria, while the other 14 patients were suffering from uncomplicated Plasmodium falciparum malaria (P.f.). Both groups were treated in Bangkok, where malaria transmission does not take place, and followed up, on the ward, for 3 weeks (P.v. group) or 4 weeks (P.f. group) after the start of therapy. In both groups DFO reduced the parasitaemia to zero within 106 and 57 h respectively. The fever clearance time was 55 and 60 h, respectively. The overall tolerability of DFO was good but 4 P.v. and 5 P.f. patients had transient visual blurring. Recrudescences were observed on average 15, respectively 10 days after the start of therapy. Only 2 P.v. patients and none of the P.f. patients remained free of recrudescences during the observation period. There was no apparent gametocytocidal effect of DFO on P.f.

Liver and intestinal flukes.

A number of trematodes besides schistosomes parasitize humans and domesticated animals. Although they do not have as great a public health impact as schistosomiasis, they are prevalent in Southeast Asia as well as among the greater than 1 million immigrants from this region to North America. The human biliary flukes include C. sinensis, O. viverrini, and O. felineus. These chronic infections are often asymptomatic but over time may cause biliary thickening, cholangitis, and a predisposition to cholangiocarcinoma. Zoonotic trematode infections include the sheep liver fluke F. hepatica and the intestinal flukes Fasciolopsis, Echinostoma, Heterophyes, and Metagonimus.