Deborah C Carson

Antibodies to blood stage antigens of Plasmodium falciparum in rural Gambians and their relation to protection against infection.

Cross-sectional and longitudinal studies were performed in a rural population living in The Gambia to examine the relationship between several in vitro assays of the host immune response to asexual stages of Plasmodium falciparum and protection from malaria in vivo. Assays included an enzyme-linked immunosorbent assay for antibodies to schizont antigens; an indirect immunofluorescence assay for total antiblood-stage antibodies; an immunofluorescence assay on glutaraldehyde-fixed parasites to detect antibodies to antigen Pf 155; an assay for serum inhibition of red blood cell invasion; a micro-agglutination assay to detect antibodies to neo-antigens on the surface of infected red blood cells; and an assay using polymorphonuclear leucocytes to detect antibodies capable of opsonizing schizont infected red blood cells. There were marked differences in the age-related pattern of response for different assays performed on sera obtained at a cross-sectional survey of 280 individuals. Examination of the correlation between the various immune responses and malariometric indices at the population level and at the individual level provided no evidence that any of the in vitro assays were related to protective immunity. The relationship between in vitro measurements of the anti-malarial immune response and protection from clinical episodes of malaria was examined in a group of 134 children aged 11 years and under who were monitored weekly throughout an entire malaria transmission season. The only immune factor to show a consistent protective effect against clinical malaria was the titre of antibodies to neo-antigens on the infected erythrocyte surface (P = 0.01). The same longitudinal techniques were used to examine the effect of two non-immunological factors, sickle cell trait and mosquito net usage, both of which showed significant protection against clinical episodes and malaria.

HIGH TOTAL AND CARDIOVASCULAR DISEASE MORTALITY IN ADULTS OF INDIAN DESCENT IN TRINIDAD, UNEXPLAINED BY MAJOR CORONARY RISK FACTORS

A prospective survey has been undertaken of a total community of 1343 men and 1149 women, aged 35-69 years at recruitment, living in Port-of-Spain, Trinidad. By comparison with adults of African descent, age-adjusted relative risks of death from all causes and from cardiovascular diseases were significantly increased in those of Indian origin (1.5 and 2.6, respectively) and reduced in those of mixed descent (0.5 and 0.3, respectively). Adults of European descent had an all-cause and cardiovascular mortality relative risk of 0.8 and 2.1, respectively. These ethnic differences in risk were not explained by systolic blood pressure, fasting blood glucose concentration, serum high-density lipoprotein or low-density lipoprotein concentration, or smoking habits. Differences in risk of cardiovascular death between Indian and European men seemed to be accounted for by the high prevalence of diabetes in Indians (19%) but other ethnic contrasts in mortality were unrelated to diabetes mellitus.

The Imo State (Nigeria) Drinking Water Supply and Sanitation Project. 2. Impact on dracunculiasis, diarrhoea and nutritional status.

Morbidity due to dracunculiasis (guinea worm disease) and diarrhoea in persons of all ages, and nutritional status of young children, were used as health impact indicators in the evaluation of the Imo State Drinking Water Supply and Sanitation Project in south-eastern Nigeria. Data were collected using repeated cross-sectional surveys and longitudinal follow-up. The study area was found to have a low level of endemicity of dracunculiasis. While no impact could be demonstrated on overall period or point prevalence rates in the cross-sectional surveys, a prospective longitudinal survey showed a significant reduction in the percentage of person-fortnights positive for dracunculiasis in areas served by the project, while the control areas showed no such change. In the cross-sectional surveys it was found that, in the project villages, those persons drinking only borehole water had significantly lower period prevalence rates one year later than others. Moreover, those living further from the nearest borehole had higher rates of dracunculiasis. An impact of the project on diarrhoea morbidity was found only in limited sub-groups of the population. A greater association with water availability rather than quality was suggested for rates in young children. The prevalence of wasting (less than 80% weight-for-height) among children aged less than 3 years decreased significantly over time in all 3 intervention villages; there was no such decline in the control villages.

Anti-sporozoite antibodies and immunity to malaria in a rural Gambian population.

A conserved repeated epitope, (NANP)3, of the circumsporozoite protein of Plasmodium falciparum has been identified previously as a putative target for artificially induced immunity to malaria. We examined the role of humoral responses to this epitope in acquired immunity to malaria in a rural African population. Seropositivity to (NANP)3 was slow to develop (9% positive in subjects aged 1-11 years; 88% in those of 30 years and above), and responses in younger subjects were transient. The poor response in younger subjects did not appear to be due to immunosuppression by concomitant blood stage parasitization. The relationship between levels of anti-(NANP)3 antibodies and parasitaemia changed from positive to negative with age. 126 subjects age 1-11 years were followed through an entire transmission season; those who were seropositive at the beginning ended the season with lower parasite rates (20% vs 59%) and experienced fewer episodes of clinical malaria (0.43 vs 0.67). However, the trend towards increasing susceptibility to clinical malaria in subjects entering the transmission season with lower levels of anti-(NANP)3 antibodies was modest, and combined cross-sectional and longitudinal data indicated that the humoral response to (NANP)3 did not play a major role in the development of immunity to clinical malaria in the population we studied.

Alternative measures of diarrhoeal morbidity and their association with social and environmental factors in urban children in The Gambia

Diarrhoeal morbidity was studied during a 15-week period of the rainy season in 244 children aged 6 to 35 months in an urban Gambian community. The average prevalence of diarrhoea was 12.0% and the mean number of episodes per child varied between 2.4 and 2.9 depending on the definition of an episode. The number of chronic episodes lasting 14 d or more was tripled when 7 rather than one diarrhoea-free days were required to define a new episode. Neither prevalence nor the number of episodes varied significantly with age or sex. There was little association between the social and environmental characteristics of the children and diarrhoeal morbidity. The implications of using differing measures of diarrhoeal morbidity are discussed.

High density lipoprotein cholesterol concentration as a predictor of coronary heart disease in West Indian men.

STUDY OBJECTIVE--The aim of the study was to determine whether the inverse association between high density lipoprotein cholesterol concentration and risk of coronary heart disease described in people of European stock was also present in other racial groups. DESIGN--The study was a prospective population survey. Cardiovascular risk factors were examined, including fasting serum lipid estimation (obtained at recruitment). SETTING--This was a community based study within a defined survey area in Trinidad. PARTICIPANTS--All men aged between 35 and 69 years within the survey area were identified and followed between 1977 and 1986. Analysis was confined to those of African, Asian Indian, and mixed descent who were free of coronary heart disease at entry (n = 960, 69% of age eligible men in the survey population). MEASUREMENTS AND MAIN RESULTS--64 men developed coronary heart disease during the study period. A strong inverse curvilinear relation was found between high density lipoprotein cholesterol and coronary heart disease incidence (p less than 0.005), independent of age or other relevant characteristics including low density lipoprotein cholesterol. CONCLUSIONS--A low serum concentration of high density lipoprotein cholesterol is a risk factor for coronary heart disease in non-whites as well as in whites.