Innate immunity, gut integrity, and vitamin A in Gambian and Indian infants.

Gut integrity, which can be measured by the urinary lactulose:mannitol excretion test, deteriorates with the introduction of weaning foods. In The Gambia, gut integrity measured monthly over 15 months in 119 infants (aged 2-15 months) was least impaired from April to June. This coincides with the time of year of maximum vitamin A (VA) intake-the mango season. Subsequently, two VA intervention studies were done in infants in India. Eighty infants attending a community health center received 16,700 IU weekly or placebo. In another study, 94 hospitalized infants were given 200, 000 IU VA or placebo: 31 received VA on admission, while the rest (32 VA, 31 placebo) received treatment on discharge. All VA-treated groups had more rapid improvement in gut integrity than the placebo groups, but no group had gut integrity normalized by Western standards. The data suggest that VA status may influence gut integrity.

The effect of vitamin A on epithelial integrity.

Vitamin A is the generic term for a variety of fat-soluble substances including retinol, retinyl palmitate and the provitamin A carotenoids such as all-trans-beta-carotene. Vitamin A is commonly known as the anti-infective vitamin and has an essential role in vision and cellular differentiation, the latter providing a unique core mechanism helping to explain the influence of vitamin A on epithelial barriers. Alterations in the epithelial lining of vital organs occur early in deficiency, suggesting a potentially important role for the barrier function. Vitamin A deficiency (VAD) is most commonly recognized in the eye. The conjunctival-impression cytology test detects the presence of larger irregular keratinized cells and the absence of mucous-secreting goblet cells, indicative of VAD. The method is simple, quick and sensitive in populations where VAD is present. In the respiratory tract, observational studies all show an association with VAD, although vitamin A supplementation studies appear to have little effect on respiratory disease. Organ-specific targeting may improve success rates. The dual-sugar intestinal-permeability test allows the effect of vitamin A supplementation to be monitored on the gastrointestinal tract. Two vitamin A supplementation studies were carried out recently in Orissa State, India. Healthy infants of weaning age were administered orally eight weekly doses of 5.0 mg retinol equivalents and hospitalized infants received one large oral dose 60 mg retinol equivalents in the form of retinyl palmitate. Improvements in gut integrity and haematological status were observed in both studies. In summary, the response of the eye to vitamin A supplementation is well established; the present review highlights some of the more recent observations examining the effects of vitamin A.

Metrifonate in the control of urinary schistosomiasis in Zanzibar.

Selective population chemotherapy using three doses of metrifonate (7.5 mg/kg body weight each time) at two-week intervals was assessed in an entire community in Kinyasini district in Zanzibar, United Republic of Tanzania. The objectives of the study were to (1) reduce the prevalence of heavy infections (defined as greater than or equal to 50 S. haematobium eggs per 10 ml of urine) by 75% in two years, and (2) reduce the overall prevalence of infection by 50% in two years. A total of 4113 people were examined at least once during the two-year period. In the initial survey the highest proportion of infected individuals was in the 10-14-year age group, and in all subsequent surveys in the 5-9-year age group. The age group with the highest proportion of heavily infected individuals was 5-9 years for all surveys. The overall reduction of prevalence of infection from survey 1 to survey 4 was 52.9% and the prevalence of heavy infection was reduced by 62.2%. The conversion rates (negative to positive in two consecutive surveys) were highest in the longest interval of 12 months and the rates of reversion (positive to negative in two consecutive surveys, without a history of treatment) were highest in the shortest interval of 4 months. Some statistically significant relationships were observed between the number of doses and the egg reduction rates. However, for the egg-negative rates, no statistically significant relationship was observed. In the 4-month interval a 67.6% egg-negative rate was observed among those who took at least one dose; with the 12-month interval a 48.3% egg-negative rate was observed. Thus, selective population chemotherapy with metrifonate was shown to reduce the prevalence and intensity of infection due to S. haematobium over a 24-month period.

Ethiopian plants with proven and suspected molluscicidal activity: a new approach in plant evaluation.

Using available information on the toxicity, phytochemistry, ethnomedical uses and geographic distribution of plants, potentially suitable species are identified for the control of intermediate hosts of schistosomiasis in Ethiopia's lowlands where endod (Phytolacca dodecandra) is not available. Of 46 species with moderate to high snail-killing potency, 35 are indigenous to Ethiopia. They include 12 plant species with molluscicidal levels similar to those of endod, four of which are particularly suitable for snail control because of their low mammalian toxicity. Another 127 species indigenous to Ethiopia belong to genera with proven molluscicidal activity. The model for plant screening used here permits preliminary assessment of the suitability of plant resources in a given region or locality for snail control programs using existing data, without prior testing of local plants, making this approach appropriate for many developing countries.

Odynophagia in patients with malignant disorders.

The differential diagnosis of odynophagia in patients with malignant disorders usually includes esophagitis due to herpes, Candida, or gastroesophageal reflux. Two cases and a review of the literature are presented that illustrate that leukemic infiltration of the esophagus and necrosis of the esophageal mucosa following chemotherapy should be considered in addition to the more commonly recognized causes. Esophagoscopy with biopsy and brushing for fungal stains is essential for the correct diagnosis since the various causes for odynophagia may be clinically and radiographically indistinguishable.

Elimination of Biomphalaria pfeifferi, Bulinus tropicus and Lymnaea natalensis by the ampullarid snail, Marisa cornuarietis, in a man-made dam in northern Tanzania.

Marisa cornuarietis is a well known ampullarid competitor/predator of Biomphalaria glabrata in Puerto Rico. For the first time in Africa a flourishing population of Marisa has been established in a small, permanent, man-made dam at Kisangara, near Moshi, Tanzania. Prior to the release of M. cornuarietis in June 1977, this dam supported thriving populations of the pulmonate snail hosts Biomphalaria pfeifferi and Lymnaea natalensis; Bulinus tropicus and the melaniid Melanoides tuberculata were also common. Some 24 months after the establishment of Marisa the three pulmonate species had been eliminated; only M. tuberculata remained at about the same population density as originally recorded. Marisa has not caused any obvious adverse environmental impact in the dam. There is at present no valid evidence that this ampullarid would be a threat to local rice production, which is the only crop at risk, but carefully designed field trials should be undertaken to confirm or refute this view. In view of the vast number of permanent, lentic habitats throughout the Afrotropical region, which act as important transmission sites of schistosomiasis and fascioliasis, the role of Marisa cornuarietis as a cost-effective biological control agent in integrated control operations deserves henceforth to be energetically explored.

Biological control of the snail intermediate hosts of human Schistosoma spp.: a review of its present status and future prospects.

The biological control of freshwater snail hosts of schistosome parasites has attracted much attention in recent years, but the efficiency of such bio-control agents has rarely been tested outside laboratory conditions. The present paper attempts to summarize the present status of biological control of snails intermediate hosts, to indicate some major gaps in our knowledge of this subject, especially those of a practical kind and, not least, to identify studies and activities which apparently merit priority for further sponsorship and support.

Molluscicides in schistosomiasis control.

Although mollusciciding can be a cost-effective method of controlling schistosomiasis transmission, only one organic molluscicide, niclosamide, is now being produced commercially, and only a few compounds are at present being tested in the laboratory. In future, improved cost-effective use of molluscicides will require more precise knowledge of schistosomiasis transmission patterns in each endemic area and improved application techniques. In snail control studies using controlled-release formulations only the organotins, especially tributyltin oxide (TBTO), have given satisfactory long-term results. However, large-scale field trials of organotin formulations have not been implemented and their use cannot be recommended as their chronic toxicity in mammals has not yet been determined. The development of molluscicides of indigenous plant origin deserves support. Endod, derived from the berries of the climbing plant Phytolacca dodecandra, is the most extensively tested plant molluscicide, but data on its chronic toxicity to non-target organisms are lacking. The mode of action of molluscicides has not been extensively studied, though knowledge of the properties required of molluscicidal molecules has contributed to the discovery and development of niclosamide and nicotinanilide. In general, molluscicides probably cause stress on the water balance system, which in gastropods in thought to be under neurosecretory control.