Objective-To demonstrate the magnitude, timing, and cause of changes in blood pressure that occur in migrants from a low blood pressure population on moving to an urban area.Design-A controlled longitudinal observational study of migrants as soon after migration as possible and follow up at three, six, 12, 18, and 24 months after migration. A cohort of controls living in a rural area who were matched for age, sex, and locality were also observed at the same periods. Viliages on the northern shores of Lake Victoria in western Kenya and Nairobi. Main outcome measures-A medical questionnaire and three 24 hour diet histories were completed by migrants and controls. Height, weight, pulse, and blood pressure were measured. Three 12 hour overnight urine samples were collected from all participants and analysed for sodium, potassium, and creatinine concentrations.Results-The mean systolic blood pressure of migrants was significantly higher than that of controls throughout the study, and the distribution of blood pressure was shifted to the right compared with controls. The mean diastolic blood pressure of the two groups diverged over time. Blood pressure differences were not due to selective migration. The migrants' mean urinary sodium:potassium ratio was higher than that of controls (p<0-001) throughout, and weight and pulse rate were also higher among migrants, although differences diminished with time.

Intensities of re-infection were monitored at three-monthly intervals after treatment of Schistosoma mansoni infections in a group of 119 Kenyan schoolchildren, whose levels of water contact were also observed. 22 children showed high reinfection intensities (greater than 100 eggs per gram of faeces) by 12 months after treatment, and were considered to be susceptible. Out of 70 children who showed low reinfection intensities during the same period (less than 30 eggs per gram), 35 showed high levels both of total water contact and of contact with sites containing infected snails. In these children, the relative lack of reinfection could not be attributed to a lack of exposure, and they were classified as resistant to reinfection. Comparison of the two groups, resistant and susceptible, revealed no difference in pretreatment intensities of infection. However, there was a marked difference in age, the mean age of the resistant group being two years greater than that of the susceptible group, within a restricted starting age range. These findings indicated that resistance was an acquired and age-dependent phenomenon, not obviously related to previous egg-induced pathology. Studies of immune responses revealed no clearcut correlate of resistance, but there were interesting differences between the two groups. Whereas anti-egg antigen responses declined after treatment to a greater extent in the resistant than in the susceptible group, antibodies mediating eosinophil-dependent killing of schistosomula rose markedly in both groups, strongly suggesting that the resistant children were being exposed to cercariae. Anti-adult worm antibodies rose sharply in both groups immediately after treatment, and thereafter declined to pretreatment levels. Although some individual children showed high levels of IgE anti-schistosomulum antibodies, there were no significant differences between the two groups. Since all children showed detectable levels of antibodies mediating eosinophil-dependent killing of schistosomula, the possibility was considered that such antibodies might be a necessary, but not a limiting, factor in immunity. Instead, the functional state of the effector cells mediating antibody-dependent killing might be limiting. Eosinophil levels, measured as an indirect estimate of eosinophil functional activity, did not differ between the two groups. There were, however, marked differences between different individuals in their capacity to produce eosinophil-stimulating monocyte mediators, and although this cannot yet be related to resistance, this aspect is worth further study.(ABSTRACT TRUNCATED AT 400 WORDS)

An enzyme-linked immunosorbent assay (ELISA) using a monoclonal antibody that recognizes a repetitive epitope on the circumsporozoite protein of Plasmodium falciparum was used in Kenya to assess malaria infections in Anopheles gambiae s.l. and An. funestus. The ELISA confirmed that 88% of 44 sporozoite-positive gland dissections were P. falciparum. The ELISA infection rate of 18.6% (n = 736) for individually tested mosquitoes for both species was significantly higher than the 10.4% (n = 537) salivary gland sporozoite rate determined by dissection. This difference was due to ELISA detection of medium and large sized oocysts on the midguts of infected mosquitoes which did not contain salivary gland sporozoites. From a series of 379 Anopheles that were cut at the thorax, ELISA tests on "head" and "body" portions showed that 29.5% of 95 positive mosquitoes contained circumsporozoite antigen in the body portion in the absence of salivary gland infections. This field evaluation demonstrates that the ELISA can most accurately be used to estimate sporozoite rates by cutting mosquitoes at the thorax and testing anterior portions.

The first human vaccines against the malaria parasite have been designed to elicit antibodies to the circumsporozoite protein of Plasmodium falciparum. However, it is not known whether any level of naturally acquired antibodies to the circumsporozoite protein can predict resistance to Plasmodium falciparum malaria. In this study, 83 adults in a malaria-endemic region of Kenya were tested for circumsporozoite antibodies and then treated for malaria. They were monitored for the development of new malaria infections for 98 days. Antibody levels, as determined by four assays in vitro, were indistinguishable between the 60 individuals who did and the 23 who did not develop parasitemia during follow-up, and there was no apparent relation between day of onset of parasitemia and level of antibodies to circumsporozoite protein. Unless immunization with sporozoite vaccines induces antibodies that are quantitatively or qualitatively superior to the circumsporozoite antibodies in these adults, it is unlikely that such antibodies will prevent infection in areas with as intense malaria transmission as western Kenya.

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