Exposure of Gambian children to Anopheles gambiae malaria vectors in an irrigated rice production area.

Variation in exposure of children to malaria vectors of the Anopheles gambiae complex was recorded in a Gambian village situated near an irrigated area of rice cultivation. Observations were made in 1987 and 1988 during two dry seasons, when pumped water was used to grow rice, and two rainy seasons, when rice was produced using a combination of irrigated and rainfed paddies. Routine collections of mosquitoes were made from under bednets. Most of these specimens were assumed to have fed on the occupants of the net and thus represented a crude measure of exposure to malaria. Most nets in the village were in good condition, but even these were a poor defence against blood-seeking mosquitoes. Two annual peaks in the numbers of An.gambiae s.l. corresponded with the irrigation of rice paddies in the dry and wet seasons. When there were few vectors in the village the frequency distribution of mosquitoes caught under nets was described best by a Poisson process. When high numbers were present the daily distributions were over-dispersed and fitted a negative binomial model. The spatial distribution of mosquitoes varied between dry and wet seasons and was related to the predominant wind direction at night, suggesting that wind assisted the dispersal of mosquitoes from their breeding sites.(ABSTRACT TRUNCATED AT 250 WORDS)

Within-person variation in urinary sodium, potassium and creatinine concentrations, and their relationship to changes in the blood pressure of adult male Gambians.

Variation in urinary electrolyte and creatinine concentrations was studied in untimed, casual specimens obtained from 65 adult Gambian males over a 15-month period during which up to nine specimens were obtained from each subject. Measurements of blood pressure were made at the times when specimens were collected. The within-person variation in urinary creatinine, sodium and potassium concentrations were all found to be larger than that between persons. Within individual subjects, the sodium concentration tended to be comparatively low, and the potassium concentration high, in specimens in which the creatinine concentration was high. This suggests that the excretion of sodium was reduced at times of relative dehydration while the excretion of potassium may have been unrelated to the urine flow. The data also suggest that changes in the state of hydration were associated with changes in blood pressure since an individual subject's pressure was inversely related to the creatinine concentration. The negative relationship of the sodium:potassium ratio with creatinine concentration casts doubt on the simple use of this ratio as an indicator of dietary intake. After adjusting for creatinine concentration by multiple regression, changes in systolic pressure were shown to be positively correlated with changes in sodium concentration. These observations show the importance of replicating measurements of urinary electrolyte concentrations. The demonstration of complex inter-relationships between blood pressure and urinary concentrations of creatinine, sodium and potassium emphasizes the need for care in the interpretation of findings from causal, untimed urine specimens.

Reproducibility of measurements of blood pressure in a tropical environment.

The reproducibility of measurements of the blood pressure of 65 adult male Gambians was investigated to assess the role that replication of measurements may have in epidemiological studies in a tropical environment. Observations were made at approximately seven week intervals over a period of 15 months and measurements were repeated three times on each occasion a subject was seen. The magnitude of the variation of an individual subject's BP between occasions, and between readings on the same occasion, was comparable with those which have been observed in studies in developed countries in temperate climates. The variation between occasions was greater than that between readings on the same occasion. There was a significant fall in systolic pressure between the first and third occasions, and a more gradual fall in diastolic pressure. The observations suggest that an individual subject's BP level would be better characterized by making a second reading on another occasion than by making three or more readings on the same occasion. These results have implications for the design of epidemiological studies and for the diagnosis of hypertension in the tropics.

Time-motion analysis of and heart rate responses to amateur ice hockey officiating.

The physical activity of referees (n = 4) and linesmen (n = 6) was analyzed from videotapes of four varsity hockey games to determine the frequency, average duration, and total time spent in each of six activity categories. The average duration of activity was low while frequency of occurrence was high. Low intensity activities occupied 96% of total time for referees and 94% of time for linesmen. Heart rate responses were recorded every 5 seconds and synchronized to the videotapes for all referees and 5 linesmen. Heart rates were above 70% of maximum for 70% of the total ice time, which was greater than expected for the observed physical activity. Psychological stress during the course of a varsity hockey game could contribute to the high heart rate responses. It is concluded that training to increase aerobic fitness is an important aspect of ice hockey officiating to increase resistance to fatigue and aid in stress management.

Ability of Anopheles gambiae mosquitoes to transmit malaria during the dry and wet seasons in an area of irrigated rice cultivation in The Gambia.

The seasonality of malaria transmission was studied in a Gambian village situated in an area where rice was cultivated. Observations were made during two dry seasons, when pump-fed irrigation was used to grow rice, and in the intervening rainy season, when rice was cultivated using a combination of irrigated and rain-fed paddies. Clinical episodes of malaria were mainly confined to the months during and soon after the rainy season. In the wet season the prevalence of parasitaemia was higher in febrile subjects than in afebrile controls but the reverse applied during the dry seasons. However, the biting rates of Anopheles gambiae complex mosquitoes in the two dry seasons (2.5 and 0.8 bites/child/night respectively) were greater than or similar to that in the rainy season (0.6 bites/child/night). The proportion of human bloodmeals (0.53 vs 0.75) and the survival of mosquitoes (parity rates of 0.41 vs 0.58) were both lower in the dry seasons than in the rains. The low prevalence of morbidity due to malaria in the dry season and the observed fall in the sporozoite rate may therefore have been due to a reduction in the vectorial capacity of the An. gambiae population. However, reduced transmission in the dry season may also have been due to the direct effect of high temperatures on the parasite in the vector.

Human IgE, IgG4 and resistance to reinfection with Schistosoma haematobium.

A well recognized feature of the immune response to parasitic helminth infections, including schistosomiasis, is the production of large amounts of specific and nonspecific IgE1,2. Immunological pathways involving IgE can lead to damage to the developing schistosomulum and it has been suggested that responses involving IgE could have evolved as protection against helminth infections. There has been no epidemiological evidence to support this idea and the only significant IgE responses known in man are those involved in the pathogenesis of allergic disease. Here we measure serological response during reinfection with S. haematobium and demonstrate that IgE antibodies in man can be beneficial. Our results support the hypothesis that the slow build-up of IgE to high levels and the early production of IgG4 antibodies, which may block IgE pathways are responsible for delaying the development of protective immunity to S. haematobium.

AIDS following mother-to-child transmission of HIV-2.

Mother-to-child infection with HIV-2 is thought to be rare, and there have been few previous reports of transmission by this route. Reports of morbidity associated with HIV-2 infection in children are also rare. We describe eight children born to mothers who were infected with HIV-2; five developed AIDS, and three were still seropositive at 17-49 months of age. The only apparent route of HIV-2 transmission was from mother to child, except for one child who had been transfused. Three of the children with AIDS died, all having decreased CD4+ lymphocytes and mitogen responses. Further studies are needed to determine the prevalence and natural history of mother-to-child transmission of HIV-2.

PIP: Eight cases of mother-to-child transmission of HIV-2 were documented by ELISA and Western blot in Gambia between January 1988-September 1989 from a hospital-based screening of 205 malnourished children, 864 subjects in a malaria study, 34 patients with probable immunodeficiency and 24 children of 17 HIV-2 seropositive mothers. AIDS was diagnosed by WHO clinical definition. Diagnosis of HIV-2 was made if sera were positive by ELISA and Western blot (LAV Blot2, Diagnostics Pasteur, Marnes-La-Coquette, France) and negative by Wellcozyme I competitive ELISA to HIV-a (Wellcome Diagnostics, Dartford, UK). The children ranged in age from 17 months-5 years, and in ponderal index from 50-90%. 6 had CD4 percentages or counts below the normal range. 7 of the 8 could only have been infected pre- or perinatally, while 1 had been transfused from her mother. The clinical features included 5 with diarrhea 1 month; 3 with Cryptosporidium, 3 with Candida, a pneumonia, an interstitial pneumonia by x-ray, a streptococcus abscess, a staphylococcus abscess, 1 infant with failure to thrive and 1 4-year old who was asymptomatic. This group of patients was more severely affected than a series reported from Guinea Bissau: their mothers also had advanced AIDS in comparison to asymptomatic mothers in the other series. While mother-to-child transmission of HIV-1 occurs in approximately 33% of children of HIV-1 seropositive mothers, these data cannot estimate the actual rate of transmission of HIV-2.

Antibody to schistosomulum surface carbohydrate epitopes in subjects infected with Schistosoma haematobium.

The binding of immunoglobulin to carbohydrate epitopes on the surface of Schistosoma mansoni schistosomula was measured with 125I-labelled protein A in sera from 67 Gambian subjects living in a focus of intense S. haematobium transmission. The levels of such antibody differed considerably between subjects and there was significant variation between age groups. The highest mean level, in subjects aged between 8 and 14 years, was significantly greater than that in older subjects. Previous studies have shown that resistance to post-treatment reinfection with S. haematobium is related to age in this focus, and is greatest in those aged 15 or more years. These differing relationships with age suggest that antibodies directed against carbohydrate epitopes on the surface of the schistosomulum do not have a major protective role in man.

Reinfection after treatment of schistosome infections.

Today, chemotherapy has a central role in the control of schistosome infections. Although the costs involved may be high in relation to local expenditures on health, externally funded mass treatment programmes can lead to large reductions in the prevalence and intensity of schistosome infections. But the benefits of treatment to a community that has been involved in a mass chemotherapy programme, or to an individual patient seen in a health centre, will be limited if reinfection after treatment is rapid and intense. Despite the efficacy of the available drugs few, if any, control programmes based on mass chemotherapy have interrupted transmission and come anywhere near to eradicating schistosome infection.

Knowledge of AIDS, use of condoms and results of counselling subjects with asymptomatic HIV2 infection in The Gambia.

A questionnaire administered to subjects seen during a serological survey in The Gambia revealed that knowledge of AIDS and HIV infection was limited. Males, those with a secondary education and people who lived in urban areas had a better understanding but only 17% of women seen in rural areas had any knowledge of the condition. Only 8% of the subjects seen had used condoms in the preceding 12 months; during this time half of them had done so on less than five occasions. Subjects with a secondary education were more likely to have used condoms. A counsellor met 31 asymptomatic seropositive subjects identified during this survey on two occasions. In the majority, the information given caused anxiety rather than modification of behaviour and, at the time of the second interview, only one subject had discussed the situation with the partner and begun using condoms. Some of the cultural factors which may affect the outcome of counselling in an African society are discussed in the light of these findings.

PIP: Questionnaires given to people from rural and urban populations seen during a serological survey in The Gambia revealed knowledge about AIDS and HIV infection to be limited. Data was received on 1,898 subjects aged at least 15 years. While only 17% of women in rural areas were aware of the existence of AIDS, males, those with secondary education, and those in urban areas demonstrated better understanding of the disease. 8%, however had used condoms over the past 12 months, with 1/2 doing so on less than 5 occasions. Secondary education generally signaled greater likelihood of condom use among respondents. A counsellor met with 31 asymptomatic, HIV-positive subjects in their homes on 2 occasions during the survey. Failing to generate behavior modifications, information provided by the counsellor largely produced anxiety. By the 2nd interview, only 1 subject had discussed AIDS and HIV infection with the partner and began using condoms. Health education programs targeted to underserved rural areas, women, and those without secondary education are severely needed. Radio, used as the key mode of message dissemination, is challenged on the basis of its audience being potentially limited due to gender and/or socioeconomic factors. Limited education, limited knowledge of AIDS in the community as a whole, sociocultural and attitudinal factors fostering social rejection of the seropositive individual, and gaining acceptability for the condom are potential obstacles to effective counselling for improved education and behavioral change. Joint sessions with partners, group sessions, and repeated exposure to a counsellor are suggested approaches. Research is suggested for alternative approaches.

Surface and species-specific antigens of Schistosoma haematobium.

Of the surface antigens identified by radio-iodination, two-dimensional gel analyses showed no similarities between those of Schistosoma haematobium and Schistosoma mansoni, thus providing a basis for the species specificity of these antigens described previously (Simpson, Knight, Hagan, Hodgson, Wilkins & Smithers (1985) Parasitology 90, 499-508). The surface antigens of S. haematobium were glycosylated and comprised an acidic polypeptide of Mr 17,000 as well as a complex set of polypeptides of approximate pI 6-7, which resolved in the Mr range 20,000-30,000. At least one of the lower Mr forms of this complex is also present in the adult worm. Limited cross-reaction was observed with S. mansoni infection sera and this may be due to a shared carbohydrate epitope. In contrast, extensive cross-reaction was observed using sera from mice immunized with S. bovis. This pattern parallels the species-specificity of vaccine-induced immunity. Extensive cross-reaction was also observed within cell-free translation products of m-RNA from adult worms of S. haematobium and S. mansoni by use of heterologous human infection sera. The few antigens which were species-specific may represent surface antigens.

Comparative trials of regimes for the treatment of urinary schistosomiasis in The Gambia.

Alternative regimes for the treatment of Schistosoma haematobium infection were compared in two trials. Praziquantel at a dose of 40 mg kg-1 appeared to cure 63% of a random sample of heavily infected subjects; significantly more than the 18% cured by three fortnightly doses of metrifonate at 10 mg kg-1. However, praziquantel led to a greater incidence of mild, transient side-effects. A single dose of metrifonate was found to be an inadequate treatment in the same group of subjects as it left 53% with an egg count of at least 100 ova/10 ml. A combination of 10 mg kg-1 of metrifonate and 25 mg kg-1 of niridazole had a similar effect to that of a single dose of metrifonate alone and it had more side-effects. Reduced doses of praziquantel had less effect on egg counts than the standard regime, but the difference was not significant in the case of 20 mg kg-1. Although a combination of metrifonate and praziquantel, each at 10 mg kg-1, had a greater effect than either constituent alone, the difference was not significant. Factors affecting the choice of drug for use in mass treatment of urinary schistosomiasis in The Gambia are discussed. The present findings suggest that the standard regime of praziquantel should be used or, if this is not possible, a three-dose metrifonate regime.

Resistance to reinfection after treatment of urinary schistosomiasis.

The process of reinfection after treatment was studied in a cohort of subjects in a focus of intense Schistosoma haematobium infection. Detailed observations were made at water contact sites of cercarial densities and of water contact by members of the cohort. Individual values of a cumulative index of exposure to infection were calculated using these observations and assumptions which were made about the effect of different water contact activities on the entry of cercariae into the skin. Among groups of subjects with an apparently similar intensity of exposure to infection, reinfection tended to be much heavier in children under 10 years of age than in 10 to 14-year-olds, while only light infections were found in the few adults who became reinfected. This trend for reinfection to decrease with increasing age, after an allowance for variation in exposure, was highly significant (p less than 0.001). These observations suggest that subjects in this area slowly acquire an increasing degree of immunity to the acquisition of S. haematobium infection which is effective in the absence of a mature egg laying infection.

Are measurements of intensity of infection or morbidity necessary to evaluate schistosomiasis control within PHC?

Techniques that can be used to monitor changes in morbidity in large scale control schemes carried out through the PHC structure by a local health administration differ from those that can be used in well funded, small scale research programmes. Above all they must be cheap, simple, rapid and objective. They should demonstrate the effects of intervention soon after it has taken place and be directed to phenomena that have high prevalences. Monitoring of liver and spleen size in S. mansoni foci to some extent meets these criteria but can only be seen as an adjunct to quantitative microscopy. Urinalysis with reagent strips, or even simpler methods, may have a more important role in evaluating control of urinary schistosomiasis and practical constraints may make it easier to carry out than quantitative microscopy. However, the latter conveys more information and is of greater value in planning and urinalysis must be seen as an inadequate substitute for quantitative microscopy.

In-vitro antibody-dependent killing of schistosomula of Schistosoma haematobium by human eosinophils.

Schistosomula of S. haematobium have been shown to be susceptible to in vitro killing by eosinophils in the presence of serum from an infected individual. The highest level of killing was found after 48 h in culture. Killing was related to the eosinophil to schistosomula ratio, being highest at 5000: 1. Killing was also related to serum concentration, being highest at a 1/10 final dilution, falling to background levels at a 1/120 final dilution. At a cell: target ratio of 2000: 1 and at a serum dilution of 1/10 eosinophils from subjects with high peripheral blood eosinophil counts were, cell for cell, more active in killing S. haematobium schistosomula than were eosinophils from subjects with lower counts. Sera taken from adults resident in an endemic area gave higher levels of killing in the presence of eosinophils than did sera taken from adults with no history of exposure.

Eosinophilia and resistance to Schistosoma haematobium in man.

We have measured the levels of infection with Schistosoma haematobium in children resident in an endemic area of The Gambia before and 3 months after successful chemotherapy and following reinfection. An exposure index was calculated from data collected on water contact, cercarial densities and infected snail densities at water contact sites. Peripheral blood eosinophil levels were recorded and the ability of serum (heat inactivated) from the children to allow killing of schistosomula of S. haematobium was examined. Of 50 children with a post-treatment egg count of less than 1 ovum/10 ml urine, 26 were classified as reinfected, acquiring greater than 1 ovum/10 ml urine over the transmission season. Twenty-four were classified as not reinfected, acquiring less than 1 ovum/10 ml of urine over the same period. These two groups did not differ with respect to their estimated age, weight or pretreatment egg counts. Children who were reinfected had significantly higher levels of exposure and significantly lower peripheral blood eosinophil counts than children who were not reinfected. At all levels of exposure children with high eosinophil counts were less likely to be reinfected than those with lower counts. But antibody-dependent, complement-independent killing of schistosomula of S. haematobium by eosinophils was barely detectable and did not differ between reinfected and non reinfected groups. These observations suggest that subjects with elevated counts are less susceptible to reinfection but the mechanisms involved are not apparent.