Zika virus may be be carried by mosquito found in NZ – Expert reaction

The Zika virus may be carried by a mosquito species found in New Zealand, according to preliminary results from Brazilian researchers.

Culex quinquefasciatus. Credit: vectorbase

Reuters reports that scientists have shown Culex quinquefasciatus – a mosquito species found in New Zealand – can be infected with the Zika virus in the lab. The researchers said more studies are needed to learn whether the Culex mosquitoes can transmit Zika in the wild.

The SMC gathered the following expert commentary on the reported findings.

Dr Julia Kasper, Principal Entomologist, NZ BioSecure, comments:
“Culex quinquefasciatus is a common species worldwide and has been introduced to New Zealand between 1830 and 1850.

“Recent laboratory results of a Brazilian study showed that local Cx quinquefasciatus could be infected with Zika but the risk for New Zealand is still very low.

“Other studies in the past have shown that this species can transmit several diseases at some level under laboratory conditions but the transmission in the wild is not proven or is only possible if a major vector (eg. Aedes aegypti) is present and the level of the disease is high in the human population. Additionally, a geographic difference in the vector competence may exist, which could relate to the introgression of a species of the same species group (Cx. pipiens) that has a general  higher vector competence. Cx. pipiens is not present in New Zealand.”

Dr José G B Derraik, Senior Research Fellow, Liggins Institute, University of Auckland, comments:

“Researchers from the Oswaldo Cruz Foundation (Fiocruz) in northeastern Brazil were able to detect Zika virus in the salivary glands of Culex quinquefasciatus mosquitoes, which had been infected with the virus in laboratory conditions.

“It seems that both the viral load in salivary glands and the rate of infection among mosquitoes were high, providing evidence that Culex quinquefasciatus may also be a vector of Zika virus. The results are preliminary, and researchers are now collecting specimens from areas where Zika virus is circulating, to identify whether the mosquitoes in the ‘wild’ are indeed carrying the virus.

“These developments indicate that the widespread claim that Zika is transmitted only by Aedes mosquitoes is probably erroneous, as it has been based on assumptions rather than on thorough investigation of the ecology of the virus.

“Importantly, these findings highlight an issue that has been misunderstood by many commenting on the risk posed by Zika virus to New Zealand. It is true that the mosquitoes said to have been transmitting the virus overseas (i.e. mainly Aedes aegypti and Aedes albopictus) do not occur in this country. However, there are 15 mosquito species present in New Zealand.

“So, while it is correct to say that the known mosquito vectors of Zika virus are not present in New Zealand, it is misguided (and potentially dangerous) to assume that we do not have mosquito vectors capable of transmitting the virus. Zika virus in particular, has been very poorly studied until the outbreak in Brazil, which means that we simply do not know whether the species of mosquitoes in New Zealand are able to transmit the virus to humans.

“Therefore, the latest findings by Fiocruz are of relevance for New Zealand. Culex quinquefasciatus was the first foreign mosquito to become established in this country, having been here since at least 1848. It is present in much of the North Island and in northern areas of the South Island.

“It is considered to be a species of ‘domestic’ habits, with a tendency to live in association with humans. It breeds in a variety of man-made habitats, including polluted waters in drains and septic tanks. Culex quinquefasciatus is considered a pest in some urban areas, and it will often come indoors to bite humans in the night time.

“As a result, even though the risk of mosquitoes transmitting viruses to humans in New Zealand is lower than in other countries, this possibility cannot be simply disregarded. Those arriving from overseas infected with an exotic virus (such as Zika) should avoid being bitten my mosquitoes in New Zealand, to minimize the chances of local transmission.”