Raw sewage as breeding site to Aedes (Stegomyia) aegypti (Diptera, culicidae)

The selection of oviposition sites by females of Aedes (Stegomyia) aegypti is a key factor for the larval survival and egg dispersion and has a direct influence in vector control programs. In this study, we evaluated the aspects of reproductive physiology of Ae. aegypti mosquitoes tested in the presence of raw sewage. Ae. aegypti females were used in oviposition bioassays according to two methodologies: (i) choice assay, in which three oviposition substrates were offered in the same cage: treatment (raw sewage), positive control (distilled water) and negative control (1% sodium hypochlorite) and; (ii) no choice assay, in which only one substrate was available. The physicochemical and microbiological analysis of the raw sewage used in this study indicated virtually no levels of chlorine, low levels of dissolved oxygen and high levels of nitrogenous compounds as well as the presence of Escherichia coli and total fecal coliforms. After 72h of oviposition, the eggs were counted and there was no statistically significant difference (p>0.05) in the oviposition rate between raw sewage and positive control in both methodologies. In addition, females were dissected to evaluate egg-retention and also there were no appreciable differences in egg retention even when raw sewage was the only substrate offered. The data also showed that egg hatching and larvae development occurred normally in the raw sewage. Therefore, the present study suggests that Ae. aegypti can adapt to new sites and lay eggs in polluted water, such as the raw sewage. These findings are of particular importance for the control and surveillance programs against Ae. aegypti in countries where the conditions of poor infrastructure and lack of basic sanitation are still an issue.

Advances in tropical diseases

There are six diseases that WHO considers as the major threat in developing countries, leprosy, filariasis, malaria, schistosomiasis, Chagas disease and leishmaniasis; and of these only malaria does not present skin lesions. These diseases are among the so called tropical diseases found in countries of tropical climate, usually infections and infestations considered exotic and rare in European and North American countries. It is extremely important for doctors of all countries to be able to provide correct pre travel counseling and to make early diagnosis and treatment, thus avoiding dissemination of these dieases to non endemic areas. The authors review some important tropical diseases seen in Brazil, as paracoccidiodomycosis, lobomycosis, myiasis, tungiasis, and cutaneous schistosomiasis and discuss new information about them.