With the caveat that there are a lot of different species of Culex mosquitoes - and earlier this week we saw a report that cast serious doubt on the ability of the Culex pipiens mosquito to transmit Zika - today researchers at Brazil's FIOCRUZ Institute have announced they have found a Culex mosquito they believe has the potential to vector the Zika virus.
The mosquito in question is the Culex quinquefasciatus - aka the Southern House Mosquito - which can be found in a broad band ranging between latitudes 36° N and 36° S.
Like the Aedes mosquitoes, C. quinquefasciatus is primarily a tropical and subtropical mosquito, although it has been reported as far north as Indiana (cite) in North America and may mate with C. pipiens (Northern House Mosquito).
Today's announcement builds on earlier studies we've seen by lead researcher Constance Ayres involving Zika and the Culex mosquito (see Fiocruz: Zika Virus Experimentally Introduced Into Culex Mosquitoes).
Today's report goes beyond simply infecting Culex mosquitoes in the lab. They have now detected naturally Zika infected Culex mosquitoes in the wild and they have shown that experimentally infected Culex mosquitoes replicate the virus about as well as does the Aedes aegypti.
From their report:
Besides the detection of virus in these tissues (intestine, and salivary gland), saliva samples were investigated expelled by mosquitoes infected by quantitative RT-PCR. The viral load found in two species ( Aedes aegypti and Culex quinquefasciatus ) was similar.
While important findings - that suggest this species of Culex has at least the potential to transmit Zika - it doesn't tell us how much of a role (if any) this species actually plays in the transmission of the virus to humans in the wild.
The report states:
From the data obtained will require additional studies to assess the potential participation of Culex in the spread of zika virus and its role in the epidemic. The current study is very important, since the vector control measures are different.
Until the results of new evidence, the zika epidemic control policy will remain guided by the same guidelines, with its central focus on the control of Aedes aegypti .
A h/t to Sharon Sanders for the link, the full (translated) announcement from FIOCRUZ follows.
Fiocruz identifies Culex in Recife with the potential to transmit the virus zika
Oswaldo Cruz Foundation (Fiocruz)
Unpublished research conducted by the Oswaldo Cruz Foundation (Fiocruz) detected the presence of zika virus in mosquito Culex quinquefasciatus (the popular muriçoca or house mosquito) collected in the city of Recife. This finding confirms the species as a potential vector of the virus that zika, a situation which, according to scientific literature, had not been proven to date.
The survey was conducted by Fiocruz Pernambuco in the metropolitan area of Recife, where the population of Culex quinquefasciatus is about twenty times greater than the population of Aedes aegypti . Preliminary results of field research identified the presence of Culex quinquefasciatus naturally infected zika virus in three of the 80 pools * (groups) of mosquitoes analyzed to date. In two of these samples they were not fed mosquitoes, indicating that the virus was widespread in the insect body and not in a recent power in an infected host.
The technique used in the experiment was quantitative RT-PCR based detection of RNA (genetic material) virus. The material of these positive pools was used to isolate the circulating virus strains in Reef, in cell culture, where it was observed cytopathic effect induced in the cells - i.e., destruction or damage of vero cells was observed, which proves the presence viral activity.
The collection of mosquitoes was made based on the addresses of the reported cases of zika in the cities of Recife and Arcoverde, obtained from the Health Department of Pernambuco State (SES-PE). The total number of mosquitoes examined in the study was approximately 500. The aim of the project is to compare the role of some species of mosquitoes in Brazil of arbovirus transmission. Priority was given to zika virus because the epidemic of the disease in Brazil and its connection with microcephaly.
In the laboratory stage, in order to investigate the vector competence of the species Culex quinquefasciatus and Aedes aegypti , mosquitoes were fed a mixture of blood and viruses, allowing the monitoring of pathogen replication process within the insect. There were two mosquito infections each infection with two different virus concentrations (104 and 106) of Ziku BRPE243 / 2015 lineage. "The smallest simulates viremia condition of a real patient. Then the mosquitoes were collected at different times: at time zero (after infection), three days, seven days, 11 and 15 days after virus infection, "says Constance Ayres, coordinator of the study.
A control group with mosquitoes fed on blood without the virus, was also maintained. Each mosquitoes was dissected to extract the intestine, and salivary gland tissues that present barriers to the development of the virus. The procedure takes place so that, if species vector is not at a given moment the development of the virus is blocked by the mosquito. However, if it is vector, virus replication occurs, spreads in the insect body and just infecting the salivary gland, from which can be transmitted to other hosts during the blood meal, the release of saliva containing virus. According Constancia, from the third day after artificial feeding has been possible to detect the presence of the virus in the salivary glands of both species of mosquito investigated. After seven days, it was observed the peak of infection in the salivary glands which was confirmed by electron microscopy.
Besides the detection of virus in these tissues (intestine , and salivary gland), saliva samples were investigated expelled by mosquitoes infected by quantitative RT-PCR. The viral load found in two species ( Aedes aegypti and Culex quinquefasciatus ) was similar.
From the data obtained will require additional studies to assess the potential participation of Culex in the spread of zika virus and its role in the epidemic. The current study is very important, since the vector control measures are different. Until the results of new evidence, the zika epidemic control policy will remain guided by the same guidelines, with its central focus on the control of Aedes aegypti .
* A pool of mosquitoes consists of 1 to 10 mosquitoes collected in each location, separated by sex and species