Saturday, September 17, 2016

Zika update 9-17-16: TORCHZ, Culex and more

Aedes aegypti feeding. Via Arizona State University Biodesign Institute

It's been an interesting couple of weeks for Zika research and news. As always, there's been good and bad news. There has also been a huge development that I'm saving for last.

In Florida, the zone of local infection in Miami Beach has been increased by three times. The number of local transmission cases are up to 93 (or were at the time of the article). The area of local infection is likely to increase further. In Puerto Rico, the outbreak is continuing to grow and the number of confirmed cases have increased to almost 20,000. Because most cases are asymptomatic, the total number of cases is likely much higher and some are predicting that as many as 1 in 4 could be infected before the outbreak stops. It's disappointing that much of the news focus has been on Florida when Zika is causing outbreaks in US territories to a much larger extent.

Also reported is that Zika can be transmitted through bodily fluids. The CDC has released an initial report on a case from Utah where an elderly patient died from Zika infection. A relative of this patient contracted the virus without the normal transmission routes. It turns out that the titer of Zika in his blood was 100,000 times above normal, and likely passed the virus to his relative through normal exposure from personal care. The CDC has also officially announced that Zika can be transmitted by sexual contact with an infected male or female. They have also released a preliminary guideline for dealing with sexual transmission. Basically, use protection or abstain from sex. 

Now for some good news. Culex pipens and Aedes triseriatus are not vectors for Zika virus. This is great news because C. pipens is a widespread mosquito and is a vector for West Nile virus. If C. pipens were a vector, then Zika could spread throughout much of the world. However, there is still some bad news. Zika virus was recently found to not only replicate in C. quinquefasciatus, but it was also found in the salivary glands where it also replicated. To be vectored by an arthropod, a virus would need to pass through the gut barrier and then migrate to the salivary glands. Replication in the salivary glands is a good indicator that the arthropod might be a vector. This is a good review on arthropod transmission of plant viruses (the principles are the same for other arboviruses). If C. quinquefasciatus is a vector for Zika, then it could spread further than we are anticipating now. Vector transmission assays still need to be conducted to determine if it is a vector or not. 

The most interesting new study on Zika is the case controlled study that confirms that Zika causes birth defects. The results showed a strong correlation between detection of Zika virus in the mother and microcephaly in the baby. Further work is required to determine the exact risk associated with Zika infection during pregnancy, but at this point the role of Zika in causing birth defects is definitive. The authors did recommend that the TORCH acronym be changed to TORCHZ. I made an infographic awhile ago on whether Zika should be added to the list or not. I'll have to update it now.

My infographic on adding Zika to the list of TORCH pathogens.