Avaliação da presença de Pythium insidiosum em imaturos e adultos de Culex quinquefasciatus

Abstract

Pythium insidiosum is an oomycete that causes pythiosis, an infection that affects different species of mammals, including humans. It inhabits swampy ecosystems in regions with tropical, subtropical and temperate climates in the world. The presence of this microorganism has been described in culicid larvae such as Culex quinquefasciatus and Aedes aegypti. The present study evaluated the ability of P. insidiosum to infect immature and adults of C. quinquefasciatus. Immatures (egg, L1, L2, L3, L4 and pupa) of C. quinquefasciatus were exposed to the zoospores (8x103 zoospores / mL) of the oomycete for 24 hours. In addition, infection from the L1 stage to adults was also assessed. The detection of P. insidiosum was carried out through microbiological culture on Bendazol and Pentachlor agar, PCR and histopathological analysis. A total of 2400 larvae in stage L1 and L2 (48 pools of 50 larvae); 2400 larvae in stages L3 and L4 (48 pools of 50 larvae); 1200 pupae (24 pools of 50 pupae) and 500 eggs (10 pools of 50 eggs) were evaluated in the microbiological analysis. It was shown that all larval stages were infected with P. insidiosum zoospores. In the molecular analysis of immature and adult forms, the presence of P. insidiosum DNA was detected only in the pools of larval stages L3 and L4. In eggs, pupae and adults it was not possible to detect the presence of the oomycete. In the histology of L4 larvae infected with P. insidiosum, no histological changes were observed in H&E. However, it is possible to observe the presence of negative images suggestive of P. insidiosum hyphae. Additionally, in the Grocott, large tubuliform structures were observed, impregnated by silver, consistent with hyphae of P. insidiosum. The results suggest that the oomycete can use the larvae of this invertebrate host to maintain its life cycle in aquatic ecosystems; however the culicid does not constitute a vector of this microorganism to vertebrate hosts.