Variable antigen type (VAT) composition of Trypanosoma brucei rhodesiense: discrepancy between results obtained using VAT-specific monoclonal antibodies and rabbit antisera.

Monoclonal antibodies have been made against clones of Trypanosoma brucei rhodesiense from the WRATAR 1 serodeme and analyzed by indirect immunofluorescence assay for specificity against homologous and heterologous clones. These antibodies were shown to be variable antigen type (VAT)-specific as they identified the majority of parasites in the homologous clones but few parasites in other clones. The reactivities of these VAT-specific monoclonal antibodies with uncloned human trypanosome isolates from Kenya were compared with the reactivities of polyvalent, VAT-specific rabbit sera on the same isolates. Different reaction patterns were obtained with the two sets of reagents and concordant reactions were less than 20%. Our data indicate that single monoclonal antibodies are not interchangeable for sera in the typing of antigenic variants of African trypanosomes, and multiple monoclonal antibodies for each antigenic variant will probably be needed.

Isolation and characterization of a new serodeme of Trypanosoma rhodesiense.

The isolation and characterization of a new serodeme of Trypanosoma brucei rhodesiense is described. A clone of organisms derived from a human infection produced chronic infections in mice. Additional clones of differing antigenic specificities were isolated from peaks of parasitemia which occurred in these mice. The variable antigen types (VATs) of these clones were determined by agglutination, immunofluorescence, and protection of actively immunized mice. Thirteen distinct VATs were isolated and designated Walter Reed Army Trypanozoon antigenic types. The described methodology and reagents, together with the chronicity of the infection produced in mice by this serodeme, provide a model for further study of immunopathology and antigenic variation in African trypanosomiasis. The use of these reagents in determining the incidence of VATs in an endemic area may allow an assessment of the feasibility of immunoprophylaxis.

Plasmodium vivax infections in U.S. Army troops: failure of primaquine to prevent relapse in studies from Somalia.

Different strains of Plasmodium vivax vary in their sensitivity to primaquine, the only drug that prevents relapses. Described are the clinical data and relapse pattern for 75 soldiers treated for vivax malaria since returning from Somalia. Following their initial attack of malaria, 60 of the 75 cases received a standard course of primaquine (15 mg base daily for 14 days). Twenty-six of the 60 soldiers subsequently relapsed for a failure rate of 43%. Eight soldiers had a second relapse following primaquine therapy after both the primary attack and first relapse. Three of these soldiers had received a higher dosage of primaquine (30 mg base daily for 14 days) after their second attack. The apparent ineffectiveness of primaquine therapy in preventing relapses suggests the presence of primaquine-resistant P. vivax strains in Somalia.

The response of Kenyan kala-azar to treatment with sodium stibogluconate.

Of 16 patients with kala-azar treated with sodium stibogluconate (0.1 ml/kg body weight a day), one died on the 12th day of treatment and nine were cured by a 30-day course, although two subsequently relapsed. Extending the course cured a further five patients, and in one patient allopurinol was used in addition before a cure was achieved. Clinical and hematological recovery began within a few days of the start of treatment, but parasites continued to be seen in splenic aspirates for 3 weeks or more.

Acridine orange diagnosis of Plasmodium falciparum: evaluation after experimental infection.

The value and role of the acridine orange/microhematocrit tube method (quantitative buffy coat [QBC] analysis) in the diagnosis of malaria remains controversial. To establish the true sensitivity of this test in comparison with the thick blood film, we studied 49 subjects who were experimentally infected with Plasmodium falciparum in 10 malaria vaccine and infectivity trials. Diagnosis was made by the acridine orange staining method 1-3 days earlier than by the thick blood film in 23 subjects (47%) and at the same time as the thick blood film in 20. On the other hand, diagnosis was made by thick blood film earlier than by the acridine orange staining method in six individuals. There were no false positive results using acridine orange among 584 specimens studied. Diagnosis was made using acridine orange at a parasitemia of less than 11 parasites/microliters of blood in 65% of cases. Where available, the acridine orange assay is clearly preferable in terms of speed and accuracy to the thick blood film for diagnosis with parasitemias of less than 150/microliters of blood, and perhaps as important, for ruling out infection with P. falciparum in a symptomatic patient.

Passive transfer of growth-inhibitory antibodies raised against yeast-expressed recombinant Plasmodium falciparum merozoite surface protein-1(19).

Purified rabbit immunoglobulin raised against yeast-expressed recombinant FVO or 3D7 Plasmodium falciparum merozoite surface protein-1 (MSP-1) 19k-D C terminal fragment (MSP-1(19)) was transfused into malaria-naive Aotus nancymai monkeys that were immediately challenged with FVO asexual stage malaria parasites. Control monkeys received rabbit immunoglobulin raised against the sexual stage antigen Pfs25 or Aotus hyperimmune serum obtained from monkeys immunized by P. falciparum infection and drug cure. Passive transfer of rabbit anti-MSP-1(19) failed to protect against homologous or heterologous challenge and, when compared with negative controls, there were no differences in prepatent periods or time to treatment. Interestingly, rabbit anti-MSP-1(19), but not anti-Pfs25, immunoglobulin, and immune monkey serum prevented the development of antibodies directed against MSP-1(19) fragment by infected monkeys, indicating that the antibodies were reactive with native MSP-1(19) antigen in vivo. The prepatent period and time to treatment was greatly delayed in the two monkeys that received Aotus immune serum, both of which developed a chronic intermittent low level infection. In vitro parasite growth inhibition assays (GIAs) confirmed the presence of inhibitory activity (40% maximum inhibition) in concentrated anti-MSP-1(19) immunoglobulin (4.8 mg/ml), but the peak concentrations we achieved in vivo (1 mg/ml) were not inhibitory in vitro. Subinhibitory levels of anti-MSP-1(19) antibodies achieved by passive transfer were not protective against P. falciparum challenge.

Characterization of Trypanozoon stocks from the South Nyanza sleeping sickness focus in Western Kenya.

220 Trypanosoma (Trypanozoon) brucei sp. stocks isolated between 1969 and 1983 from the Lambwe valley sleeping sickness focus in South Nyanza, Western Kenya, were characterized by isoenzyme electrophoresis using 12 enzymes. 12 different zymodemes of T. (T.) b. rhodesiense were isolated from patients during the 13-year period and identical stocks were also found in cattle, reedbuck (Redunca redunca) and tsetse (Glossina pallidipes). Cattle may have played an important role in maintaining and increasing peridomestic transmission of trypanosomes during the 1980 outbreak of sleeping sickness in the valley, even though they themselves suffered heavy mortality. Sleeping sickness in Lambwe valley is unlikely to have been introduced from elsewhere, since T. (T.) b. rhodesiense stocks isolated from the valley were different from those from neighbouring epidemic areas. Alternatively, the recent outbreak may have been caused by the increased transmission associated with an expanding tsetse population. The possibility that genetic exchange contributed to the biochemical diversity of the trypanosomes examined is discussed.

Allopurinol in the treatment of visceral leishmaniasis.

Allopurinol was used in the treatment of 10 patients with kala-azar. Of six patients who had previously failed to respond satisfactorily to Pentostam, "cures" were achieved in four. However, it was necessary to add Pentostam to the allopurinol in one, and another relapsed after apparent "cure" but again responded to allopurinol. The response of four patients who had had no previous treatment for kala-azar was less satisfactory.