West Nile virus passes from female to eggs, but less so from larvae to adults

March 5, 2013

In California Culex mosquitoes are considered to be the principle vectors of West Nile virus (WNV), which infects birds, humans, and other mammals during the summer. In addition, these mosquitoes may also serve as overwintering reservoir hosts as the virus is passed "vertically" from female mosquito to egg, then larva, and then adult.

To find out how often this happens, California researchers monitored WNV in mosquitoes in the field and in the lab, and observed how the virus is transmitted between generations and between insect stages. The results are published in the March, 2013 issue of the in an article called "Experimental and Natural Vertical Transmission of by California Culex (Diptera: Culicidae) Mosquitoes."

In the field, the researchers captured 934 and found in 34 of them. These 34 females then laid egg rafts, and the first-instar larvae from nine of them tested positive for the virus.

In the lab, two groups of infected females were observed, one to see how many transmitted the virus to their first-instar larvae, and the other to see how many transmitted the virus all the way to the adult stage of their progeny. Overall, were significantly higher when measured for first-instar larvae compared with adults. In the first group, they found that 23 out of 28 infected females transmitted the virus to their larval offspring, while in the second group only two out of 25 adult offspring of infected females were found to carry the virus. This demonstrates that a considerable number of may be lost during to the adult stage, but it is unclear why.

The percentage of females passing on the virus was also estimated by testing egg rafts. Interestingly, the presence of WNV in egg rafts did not ensure that the larvae would become infected. Among females transmitting to larvae, seven had negative egg rafts and positive larvae, and one had a positive egg raft and negative larvae. One possible explanation is that larvae may acquire the virus by feeding on infected egg rafts after emerging.

The authors conclude that future studies are needed to explain how WNV is vertically transmitted, if larvae can become infected by feeding on infected eggs, and why the virus seems to be frequently degraded during metamorphosis.

"This could be used as a tool for identifying foci of virus transmission during the WNV season," said Brittany Nelms, one of the authors of the study. "Although we found that the is lost from the larval to the adult stage, we can still identify areas where vertical transmission is taking place in nature."

Explore further: Heat, rainfall affect pathogenic mosquito abundance in catch basins

Related Stories

Heat, rainfall affect pathogenic mosquito abundance in catch basins

July 6, 2012
(Medical Xpress) -- Rainfall and temperature affect the abundance of two mosquito species linked to West Nile Virus in storm catch basins in suburban Chicago, two University of Illinois researchers report.

Did wild birds cause the 2010 deadly West Nile virus outbreak in Greece?

November 11, 2012
In 2010, 35 people in Greece died from a West Nile virus (WNV) outbreak, with a further 262 laboratory-confirmed human cases. A new article published in BioMedCentral's open access journal Virology Journal examines whether ...

Continental mosquito with 'vector' potential found breeding in UK after 60 year absence

February 9, 2012
A species of mosquito has been discovered breeding in the UK that has not been seen in the country since 1945. Populations of the mosquito, found across mainland Europe and known only by its Latin name Culex modestus, were ...

Recommended for you

Google searches can be used to track dengue in underdeveloped countries

July 20, 2017
An analytical tool that combines Google search data with government-provided clinical data can quickly and accurately track dengue fever in less-developed countries, according to new research published in PLOS Computational ...

MRSA emerged years before methicillin was even discovered

July 19, 2017
Methicillin resistant Staphylococcus aureus (MRSA) emerged long before the introduction of the antibiotic methicillin into clinical practice, according to a study published in the open access journal Genome Biology. It was ...

New test distinguishes Zika from similar viral infections

July 18, 2017
A new test is the best-to-date in differentiating Zika virus infections from infections caused by similar viruses. The antibody-based assay, developed by researchers at UC Berkeley and Humabs BioMed, a private biotechnology ...

'Superbugs' study reveals complex picture of E. coli bloodstream infections

July 18, 2017
The first large-scale genetic study of Escherichia coli (E. coli) cultured from patients with bloodstream infections in England showed that drug resistant 'superbugs' are not always out-competing other strains. Research by ...

Ebola virus can persist in monkeys that survived disease, even after symptoms disappear

July 17, 2017
Ebola virus infection can be detected in rhesus monkeys that survive the disease and no longer show symptoms, according to research published by Army scientists in today's online edition of the journal Nature Microbiology. ...

Mountain gorillas have herpes virus similar to that found in humans

July 13, 2017
Scientists from the University of California, Davis, have detected a herpes virus in wild mountain gorillas that is very similar to the Epstein-Barr virus in humans, according to a study published today in the journal Scientific ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.