Monday, 25 April 2016

Biting assumptions...

This is not Aedes albopictus.
But it is a mosquito.
The Pan American Health Organization (PAHO) and the World Health Organization (WHO) Zika Epidemiological Update (status as of 21 April 2016) had some nice Zika virus (ZIKV) graphs from different - that is, not Brazil and Colombia - ZIKV affected countries.[1] 

It also had a very interesting snippet - that the Mexico Epidemiological Surveillance System (SINAVE) has reported detection of ZIKV in wild caught Aedes albopictus mosquitoes in Mexico.[1] The were identified using real-time RT-PCR and confirmed 1st April 2016.

That's a first for Mexico and also a first for the Americas in terms of detecting the variant of the Asian lineage of ZIKV that has been running rampant across the region, in a presumed vector. To date, all the detection have been from (many) humans, a howler monkey and a marmoset.[1,4,]

The 1966 Malaysian Ae.aegypti
ZIKV isolate is HQ234499 at the top
of the Asian lineage branch
The only (that I know of - please let me know if there are others) other reported detection of ZIKV from wild-caught (not lab infected) Aedes aegypti mosquitoes was a divergent virus in 1966 in Malaysia.[2,3] In that study, culture of infectious virus was also achieved. In Mexico - only ZIKV RNA was detected. It is also possible that the virus sucked up ZIKV from an infected animal or human but that these particular Ae.albopictus might not able to effectively infect other animals or humans. We'd need to know whether the mosquito testing was of whole mosquitoes or mosquito midguts, thoraces, heads, legs, saliva or salivary glands (this being the money part of the mozzie as it shows the virus infected the mosquito, left the midgut and spread, ending up in the part that will produce the infectious spit that is vomited while feeding on the animal). 

Detection in midgut only indicates ingestion whereas finding virus in the legs for example, indicates disseminated infection of the mozzies (ingested, infected, whole body spread). Whole squashed mozzies alone = more work needed. Nonetheless - this is a very valuable finding and its great to see someone is pursuing this and succeeding. And talking about it.

Up until this point we'd been assuming mosquitoes were the major transmitter because they had been in the past - as far as we knew. Now we have a little hard data.

References...

  1. http://www.paho.org/hq/index.php?option=com_content&view=article&id=11599&Itemid=41691&lang=en
  2. ISOLATION OF ZIKA VIRUS FROM AEDES AEGYPTI MOSQUITOES IN MALAYSIA
    http://www.ncbi.nlm.nih.gov/pubmed/4976739
  3. Genetic Characterization of Zika Virus Strains: Geographic Expansion of the Asian Lineage
    http://journals.plos.org/plosntds/article?id=10.1371/journal.pntd.0001477
  4. http://www.paho.org/hq/index.php?option=com_docman&task=doc_view&Itemid=270&gid=34183&lang=en