Detection of Wuchereria bancrofti in the city of Sao Luis, state of Maranhao, Brazil: New incursion or persisting problem?

BackgroundThe elimination of lymphatic filariasis (LF) from Brazil by 2020 was not accomplished; however, this goal can be achieved in the upcoming years with the assistance of specific strategies. The surveillance of LF can be performed using molecular xenomonitoring (MX), a noninvasive method used to infer the presence of the parasite in the human population. Herein, Sao Luis (state of Maranhao) was the first city to be investigated to identify whether LF transmission in Brazil has been interrupted and if there were any new incursions. Methodology/Principal findingsMosquitoes were collected by aspiration at 901 points distributed among 11 neighborhoods in Sao Luis with records of patients with microfilaremia. Pools of engorged or gravid Culex quinquefasciatus females were evaluated by WbCx duplex PCR with endogenous control for mosquitoes and target for W. bancrofti for determining the vector infection rate. Among the 10,428 collected mosquitoes, the most abundant species were C. quinquefasciatus (85%) and Aedes aegypti (12%). Significantly larger numbers of mosquitoes were collected from the neighborhoods of Areinha and Coreia (p<0.05). MX performed using PCR validated 705 pools of engorged or gravid females, fifteen of which were positive for Wuchereria bancrofti in two neighborhoods. ConclusionsThe high density of engorged C. quinquefasciatus females per home, inadequate sanitation, and detection of W. bancrofti-infected mosquitoes in the city of Sao Luis represent a warning of the possible upsurge of LF, a disease that is still neglected; this underscores the need for the ostensive monitoring of LF in Brazil. Author summaryIn the diagnosis of lymphatic filariasis (LF) using molecular xenomonitoring, the collection of mosquitoes is a critical step. Catching insects within the residence after the blood meal is ideal because the use of engorged or gravid females increases the odds of finding the parasite ingested during a meal and indicates the occurrence of microfilaremia patients in the region. In Sao Luis, more than ten thousand adult mosquitoes were removed from the residences in the study period. Considering the confirmation of the pools of Wuchereria bancrofti-infected C. quinquefasciatus females, it is necessary to initiate chemotherapeutic treatment to avoid the recrudescence of LF. Several cities in Brazil have environmental and socioeconomic profiles similar to those found in Sao Luis, especially those that were considered endemic for LF at some time in the public health history of the country. The collection and diagnostic methods used in the present study can and should be used in other Brazilian states for verifying the interruption of LF transmission.