Researchers in Brazil announced Thursday the “presence of the Zika virus” in Culex mosquitoes (the common house mosquito) in the eastern city of Recife. The findings were released with a word of caution: “The obtained data will require additional studies in order to assess the potential participation of Culex in the spread of Zika and its role in the epidemic.”
Researchers collected 500 mosquitoes and divided them into pools of between 1 and 10 mosquitoes. They found the virus in three pools of mosquitoes. The presence of the virus in these mosquitoes does not mean they can transmit the virus.
Before this study was completed by the Oswaldo Cruz Foundation (Fiocruz), Zika was thought to be carried solely by the Aedes aegypti mosquito. Culex mosquitoes are “20 times greater than the population of Aedes aegypti” in the Recife metropolitan area, according to the study.
Fiocruz is a public institution attached to the Brazilian Ministry of Health. It is one of Brazil’s oldest and most respected health care institutions and has been at the forefront of the fight against Zika.
The World Health Organization said the new research is a welcome addition to the existing body of Zika research but also cautioned that more study is needed to confirm whether Culex mosquitoes can transmit the Zika virus.
Dr. Raman Velayudhan, an expert in vector control and part of the WHO Zika response team, wrote in an email, “we also need to know the infection rates of wild-caught Culex compared to Aedes. Studies in other affected countries confirm the transmission by Aedes only. As we learn more, our interventions, recommendations and risk assessments will evolve to reflect new knowledge.”
Tom Skinner, the U.S. Centers for Disease Control and Prevention’s senior press officer, said Thursday in response to the study’s findings, “the study would need to be replicated to have a better understanding of possible implications. Body of scientific evidence to date clearly points to Aedes being the primary vector implicated in Zika outbreaks.”
Velayudhan said the same mosquito-control measures used against Aedes mosquitoes work against Culex quinquefasciatus mosquitoes, the species identified in this study.
A U.S. study published this week in the journal Emerging Infectious Diseases found that a different type of Culex mosquito, Culex pipiens, was not capable of transmitting the Zika virus, leading researchers to conclude that transmission in the U.S. from these mosquitoes is unlikely.
The virus has been spreading across the Americas since last year. The World Health Organization declared a public health emergency of international concern in February. Since then, researchers have found the virus can cause a devastating birth defect, called microcephaly, in babies born to women who were infected with the virus during pregnancy.
