Sunday, September 04, 2016

BioRxIv: Zika Virus Replication In Culex Quinquefasciatus In Brazil

Credit Wikipedia


As we've seen many times, it is not all that unusual to see conflicting results from similar scientific studies conducted by reputable research teams.

Just last month, in When Flu Vaccine Studies Collide, we looked at widely differing assessments on the effectiveness of the nasal spray (LAIV) flu vaccine from here in the United States and elsewhere in the world. 

On another front, over the past six months we've seen conflicting reports over whether non-Aedes mosquitoes - like the common  house (Culex) mosquito - can transmit the Zika virus.

In mid-July, we saw a press release from from FIOCRUZ (Fundação Oswaldo Cruz) - one of the oldest and most prestigious scientific research institutes in South America - describing A Culex Mosquito With The Potential To Transmit Zika.
That announcement built on earlier studies we'd seen by lead researcher Constance Ayres involving Zika and the Culex mosquito (see Fiocruz: Zika Virus Experimentally Introduced Into Culex Mosquitoes).

But that announcement also stated they had detected naturally infected Culex mosquitoes in the wild and that experimentally infected C. mosquitoes replicated the virus nearly as well as does the Aedes aegypti.

By contrast (also in July) in a letter to the EID Journal (see Culex pipiens and Aedes triseriatus Mosquito Susceptibility to Zika Virus) - attempts by researchers from the University of Wisconsin to experimentally infect these non-Aedes mosquitoes strongly suggested they were not competent vectors of Zika. 

And last week, in Eurosurveillance: Experimentally Infected Culex Mosquitoes Unable To Spread Zika, we saw two more studies that cast even greater doubt on the role of Culex mosquitoes in the spread of Zika.

While the prospect of Culex mosquitoes as competent vectors for Zika appeared to be dimming, scientists never like to say `never'.

Particularly when they continue to see conflicting research.

Which brings us to the early publication (h/t @MackayIM) of the study referenced in the July press release from FIOCRUZ -  that while not yet published in a peer-reviewed journal - has been offered as a preview on the BioRxiv (Bio Archive) site.

Follow the link below to read:

Zika virus replication in the mosquito Culex quinquefasciatus in Brazil
D. R. D. Guedes 1 † , M. H. S. Paiva 2 † , M. M. A. Donato 1 , P. P. Barbosa 1 , L. Krokovsky 1 , S. W. dos S. Rocha 1 , K. L. A. Saraiva 1 , M. M. Crespo 1 , R. M. R. Barbosa 1 , C. M. F. Oliveira 1 , M.A. V. Melo-Santos 1 , L. Pena 3 , M. T. Cordeiro 3 , R. F. de O. França 3 , A. L. S, de Oliveira 4 , W.S. Leal 5 , C. A. Peixoto 1 , C. F. J. Ayres 1 * .

As to what explains the difference in their findings, there are a lot of possibilities, including differences in methods. But one possibility:
There are hundreds of anthropophilic mosquito species around the world, including dozens of varieties of Culex. It is conceivable that what is true for one variety, in one region of the world, may not hold true for all of them. 

As much as we'd like quick and definitive answers, science is often messy, progress is made in fits and starts, and `Eureka!’ moments of sudden clarity are exceedingly rare. 

Which means we'll have to wait for more data before we can say with any confidence what role (if any) non-Aedes mosquitoes play in the spread of Zika.

Stay tuned.