Falciparum malaria in a displaced Haitian population.

Falciparum malaria was a major problem among displaced Haitians in temporary camps at the US Naval Base, Guantanamo Bay, Cuba. From December 1991 to March 1992, 235 cases of unmixed falciparum malaria were diagnosed in the laboratory, giving a cumulative attack rate of 160 per 10 000 camp residents. All cases were successfully treated with oral chloroquine. Children under 16 years of age, and especially females, were at substantially higher risk of infection (attack rate 481/10 000 versus 278/ 10 000 for males in the same age range). Malaria attack rates by place of birth in Haiti were calculated per 10 000 people as Cayemite, 530; Baraderes, 375; Pestel, 285; Port Au Prince, 247; and La Gonave, 36. The time to onset of clinical malaria after embarking at the Naval Base ranged from one to 58 d. No malaria transmission was demonstrated in the migrant camp. A non-systematic survey showed a 1.7% prevalence (95% confidence interval +/- 1.9%) of falciparum malaria among asymptomatic residents. Health practitioners in areas that may receive Haitian migrants should plan to care for malaria and preventive medicine measures are indicated, as imported malaria could be transmitted in areas where competent vectors are indigenous.

Improvement of the merthiolate-iodine-formalin (MIF) fecal technique for hookworm, Trichuris trichiura, and Ascaris lumbricoides eggs.

The merthiolate-iodine-formalin (MIF) technique to detect human intestinal parasites in feces was inefficient for the detection of hookworm and Trichuris trichiura eggs. Addition of a saturated-brine flotation step increased recovery of hookworm eggs by 77% and Trichuris trichiura eggs by 87%. Recovery of Ascaris lumbricoides also was increased by 71%. This was a significant improvement in the sensitivity of the MIF technique for these 3 kinds of human parasite.

Specific identification of Plasmodium sporozoites using an indirect fluorescent antibody method.

The specific identification of plasmodial sporozoites is not possible on morphological grounds. This study presents a serological method for the identification of sporozoite species, indicating the suitability of this approach for detection and determination of sporozoites in wild vectors collected from malaria endemic areas. Specific antisera and monoclonal antibodies prepared against each of two species of rodent malaria (Plasmodium berghei or P. yoelii) were evaluated for their ability to discriminate among sporozoites of different malaria species (P. vivax, P. gallinaceum, P. berghei, P. yoelii) from varied host types. Antisera produced by intravenous immunization of rabbits or mice and hybridoma-produced monoclonal antibodies reacted only with homologous sporozoites in an immunofluorescent antibody test. Antisera produced by intravenous challenge showed no significant difference in reactivity with fresh sporozoites as compared with sporozoites frozen at -80 degrees C for up to six months, whereas antisera produced by infective mosquito bites showed reduced sensitivity to frozen-stored homologous sporozoites and some cross-reactions with heterologous sporozoites. Antisera prepared against the erythrocytic stages of P. berghei or P. yoelii also cross-reacted with sporozoites of all four plasmodia tested, indicating that it is advantageous to use anti-sporozoite antibodies for the identification of malaria sporozoite species by means of serological tests.

Rapid, large-scale isolation of Plasmodium berghei sporozoites from infected mosquitoes.

The discontinuous gradient technique for recovery of malarial sporozoites from mosquitoes (Beaudoin et al., 1977) has been modified to speed up recovery and prevent sensitization of mice by components of the gradient which contaminate the sporozoites used as antigen. Mouse serum was substituted for BSA in the gradient because the latter produced hypersensitivity. Best results were obtained with gradients consisting of Medium 199, Renografin and mouse serum. Heavy and light solution of gradient components are layered in a centrifuge tube. Centrifugation of comminuted, infected mosquitoes applied to the top of the discontinuous gradient concentrates sporozoites at the interface. Sporozoites recovered from the gradient were infective, immunogenic, and relatively free of mosquito tissue. This improved method enables recovery of 100,000 sporozoites from each Anopheles stephensi infected with the ANKA strain of Plasmodium berghei. As many as 2,800 mosquitoes have been processed in 2 hr without a significant decrease in yield.

Malaria vaccination with irradiated sporozoites: serological evaluation of the antigen and antibody responses.

Vaccination against Plasmodium falciparum with attenuated sporozoites is the goal of the US Navy's Malaria Vaccine Program. One requirement in the development of this vaccine is an immunological test to study the sporozoite antigen and immune responses it induces. Using an indirect fluorescent antibody test (IFAT) and P. berghei in the mouse or rat as a model, we have made significant progress toward this goal. Four antigens were detected in vaccine preparations: sporozoite-specific antigens, mosquito antigens, antigens on the sporozoite that are common to erythrocytic stages, and bovine serum albumm, an antigenic element of the isolation medium no longer employed. The IFAT was a reliable monitor of vaccination in a mouse and rat model in conjunction with protection to challenge. The test was a sensitive monitor of vaccine quality. Anamnestic responses to bites of infected mosquitos were detected in mice previously immunized with irradiated sporozoites.

The use of membrane screen filters in the isolation of Plasmodium berghei sporozoites from mosquitos.

An improved procedure is presented for the isolation of Plasmodium berghei sporozoites from host mosquitos. The method employs filtration through a series of Nuclepore membranes followed by two consecutive centrifugations of the filtrate layered over Renografin-60 solutions of different densities. A Coulter Counter was used to compare isolations prepared by this technique with those prepared by a routinely employed discontinuous gradient method. When the sporozoite concentration in each preparation was standardized at 300 sporozoites per ml, isolations prepared by the new technique were significantly cleaner than isolations prepared by the discontinuous gradient method, containing an average of 1706 total particles per ml compared with 46 107 total particles per ml. The latter procedure was more effective, however, in removing viable microorganisms. Sporozoites isolated by both techniques were similar in immunogenicity and virulence.