Monday, February 08, 2016

Climate change may exacerbate bird flu, Zika, and other infectious diseases

Sonia Shah has a booklet-length article (or “opinion”) in the New York Times Sunday Review, “Is Bird Flu Back?”, titled “What you get when you mix chickens, China and climate change” online.  The writer gives a vivid account of her personal visit to village and farm areas in  Guangdong province near Guangzhou, with the “closeness” of people to their poultry. 
She also makes strong arguments that climate change, with accelerated warming in polar latitudes (it was actually above freezing one day at the North Pole around Christmas, as a result of a big Atlantic storm) makes it easier for birds and their diseases to migrate to the Americas.

We still don’t seem to have done much work on vaccines against H5N1, H9N7, H10N8, etc.  So far, none of them seem to move person to person, once someone is infected from birds.  They also seem to be quite virulent, going to the lungs and GI tract.  It’s not clear if a pandemic would cause the catastrophic illnesses we saw in 1918, but it sounds possible.

In the meantime, the CDC has issued guidelines regarding possible sexual transmission of Zika, posing an apparent risk to unborn children.  Zika often produces mild or no symptoms in most adults, and there are concerns over whether mosquitoes could carry them in the US from an infected person eventually, or whether the virus could be transmitted in saliva.  Arboviruses tend to be rather species specific in vectors, so the former idea sounds unlikely.  The saliva exposure is speculative.  But one can imagine sci-fi scenarios (and the moralizing that follows) where the “behavior” of otherwise healthy adults is seen as amplifying a Trojan virus that endangers the unborn or leads to sterility.  We saw that ugly debate in the 1980s.     

There is also information suggesting that Zika virus can persist in male semen a long time after it has disappeared from the blood;  the reproductive system is somewhat shelter from the rest of the immune system.  A vaccine is said to be 18 months away. 
The Dallas Morning News has a perspective by Seema Yasmin, “Why is Dallas ground zero for infectious diseases like Zika?” which looks back to the Ebola case in 2014. 

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