Serologic and parasitologic studies of Entamoeba histolytica in El Salvador, 1974-1978.

Serologic and parasitologic studies were done in El Salvador, C.A., from 1974-1978 to examine the reliability of the diagnosis of Entamoeba histolytica infection in an endemic area and to confirm the estimates of morbidity and mortality due to amebiasis. The results suggest that infection with E. histolytica is common, but the estimated prevalence is too high. Misdiagnosis occurring in hospital and public health laboratories was documented. Data collected from examining family members of persons with E. histolytica infection and disease indicate that most infections are asymptomatic, and support the hypothesis that estimates of morbidity and mortality rates are excessive.

Seroepidemiologic investigations of malaria in Guyana.

The results of longitudinal seroepidemiologic malaria surveys with the indirect haemagglutination test in four sectors in the interior of Guyana did not suggest recent malaria transmission. Indigenous malaria cases had not been detected in these sectors since 1968 but malaria surveillance here had been incomplete. The multi-stage cluster sampling method used proved to be efficient and permitted the survey of a large and sparsely populated area to be concentrated in relatively few localities. Observation of a group of 147 seropositive and seronegative persons after one year showed a four-fold or greater decline of antibody titres in five per cent of the cohort population and no such titre increases were seen, thus confirming the absence of recent malaria infections. Seropositivity rates were higher in persons with a history of malaria than in those without such a history. Collecting blood on filter paper facilitated obtaining material for serologic testing especially in the younger age group and no refusals were encountered. This advantage compensates for the slight loss in sensitivity when filter paper eluates are titrated instead of sera. The difference between the past infection probabilities of the age groups over and under 20 years old suggests that the disappearance of malaria from the interior was related more to the elimination of malaria transmission along the coast than to the specific malaria campaign in the interior.

Plasmodium brasilianum antigen for use in the indirect hemagglutination test.

Antigen was prepared from Plasmodium brasilianum harvested from an infected spider monkey. This antigen was attached to aldehyde-fixed, human type O cells, and was tested against sera from human cases of P. malaria, P. vivax, P. falciparum, and P. ovale infection, and sera from noninfected persons. At dilutions of 1:16 or greater the antigen failed to react in sera from noninfected persons. It reacted at titers of 16 or above with sera from 85% of the persons with P. malariae infection, 83% with P. vivax infection, 70% with P. falciparum infection, and 70% with P. ovale infection.

Interpretation of IHA titres for the study of malaria epidemiology.

The results of IHA test surveys of persons with malaria parasitaemia in Ethiopia and the Philippines suggest that the antibody response may be influenced by the frequency and intensity of the antigenic stimulations and also be age-dependent. Antibody frequency distribution curves from four different areas suggest that the shape of such curves can provide some information about the endemicity of malaria. Results of similar and of parasitological surveys in Bangladesh, Ethiopia, Haiti, and the Philippines were compared and related to available malaria surveillance information. The results indicate that a serologic population profile may provide an indication of the history and status of malaria. Technical aspects of the IHA test are reviewed; it may be desirable to use homologous antigens instead of a simian Plasmodium antigen. To obtain the most useful additional epidemiological information about a malaria situation, serologic data need to be age-related, and longitudinal surveys are usually more informative than a cross-sectional survey.

Seroepidemiological studies by indirect haemagglutination tests for malaria. Military recruit collections from Argentina, Brazil, Colombia, and the United States of America.

Seroepidemiological studies of 10 956 sera of military recruits from 4 countries in the Western Hemisphere suggest that the indirect haemagglutination test employing an antigen prepared from Plasmodium knowlesi adsorbed to human group O erythrocytes may be useful in epidemiological studies of malaria. Based on a titre of 1: 8, or higher, in a micro-titration of serum, the prevalence of serological reactors in the collection of sera from USA recruits was 0.9%, in the Argentina collection 4.6%, in the Brazil collection 20.8%, and in the Colombia collection 21.3%. In Brazil and Colombia the distribution of serological reactors correlated with the distribution of malaria as determined by active and passive surveillance. In Argentina, serological reactors were found in states where active and passive surveillance indicated that malaria had been eradicated years ago.