Uso do xenomonitoramento como ferramenta para avaliação da interrupção da transmissão da filariose linfática nas cidades de Belém (PA) e Maceió (AL)

Abstract

Lymphatic filariasis is an infection caused in the Americas by the helminth species Wuchereria bancrofti. This parasite exclusively infects humans, the only source of infection for the mosquito vector Culex quinquefasciatus. In Brazil a national programme to eliminate Bancroftian filariasis was implemented and currently distribution of the infection is almost restricted to Recife and its Greater Metropolitan area, in Pernambuco State. In Maceió-Alagoas, and Belém-Pará, lymphatic filariasis transmission are about to be eliminated. As part of the assessment of the effectiveness of control strategies for filariasis in these two cities, molecular xenomonitoring was conducted in order to verify interruption of Wuchereria transmission. Xenomonitoring is polymerase chain reaction (PCR)-based method for the detection of W. bancrofti in mosquitoes. This technique detects parasite DNA by PCR in blood engorged female mosquitoes collected in an endemic area. Xenomonitoring is a useful and sensitive marker to estimate natural infection with filarial larvae in the vector mosquitoes. It is also a tool for assessing indirectly filariasis prevalence in the human population because it reveals blood microfilariae recently ingested by the insect. Field collected mosquitoes, mainly through the xenomonitoring, from Maceió and Belém, two areas under the filariasis control programme in Brazil, were processed by PCR assay for the detection of infection. A simple and rapid DNA extraction method was standardized. Identification of the parasite was based on amplification of the SspI repeat DNA sequence to W. bancrofti, using species specific NV1 and NV2 primers. A total of 2,583 mosquitoes from the three city sectors endemic for lymphatic filariasis in Maceió, and 59,583 from the eight administrative districts of Belém, were submitted to PCR analysis. No W. bancrofti-infected mosquitoes were found, suggesting an interruption of filariasis transmission in the studied areas. The objective of the World Health Organization (WHO) is to eliminate filariasis as a public health problem in the world by the year 2020. Brazil is among the countries that joined the WHO global efforts. According to the present data, Belém and Maceió will achieve that goal antecipating WHO target date for the global elimination. Nevertheless, to maintain this trend, surveillance measures must be conducted in order to detect and promptly treat patients, to prevent the risk of resurgence of foci apparently under control.