Friday, January 29, 2016

Debunking the myths surrounding the Zika virus outbreak in South America

So there have been several conspiracy theories presented to suggest that the Zika virus outbreak in Brazil was man made. I'll try and address two regarding the outbreak that I have come across.

The first and easiest CT to debunk is the the notion that the Zika virus outbreak occurred because of the field trial of the genetically engineered mosquitoes in Brazil. This is based on the outbreak occurring after the field trial (conducted in 2011) and starting in the general area the field trial happened. However, when the evidence is examined, this CT falls apart.

The location of the Zika virus outbreak in Brazil, 2015

The interesting thing about this image is that it is shows the occurrence of microcephaly cases and the start of the outbreak. A similar image with the heading intact can be found here. But this map does show an important clue to the start of the outbreak. A large number of microcephaly cases are concentrated around the city of Natal in the state of Rio Grande do Norte (on the eastern tip where the cases are clustered). This is in fact the city where symptoms similar to Zika (but not Dengue or Chikungunya) were first described in Brazil. This next connection is a stretch; the location of the field trials of GE mosquitoes conducted by Oxitec. 

The "location" of the Oxitec GE mosquito field trials
The problem here is that the Oxitec field trials happened in Juazeiro in the state of Bahia and this map is pointing at Juazeiro do Norte in the state of CearĂ¡. Juazeiro do Norte is about 626.1 km from Natal and 371.8 km from Juazeiro. It is 880 km from Juazeiro to Natal (note these are driving distances). So, the actual city where the field trials began is a bit further away from the start of the outbreak. It's still plausible, but less likely. Part of this is because mosquitoes can only travel about 58.2 m so that is a great distance for them to be carried. It also helps to understand exactly what the trials tested.

The field trial tested the ability of GE male Aedes aegypti mosquitoes to impact the population size in the trial location.The results were astounding with a population reduction of >90%. The way that the mosquitoes were altered plays a huge role in the success of the experiment. The mosquito has been genetically sterilized in an improvement on the sterile insect technique. Normally, male insects are sterilized with radiation but that has the drawback of zapping insects with radiation which can reduce their fitness. The GE mosquito is still as fit as any other male mosquito, it just doesn't produce viable offspring. But there is a catch, a common antibiotic called tetracycline can interfere with the genetic mechanism that causes the mosquito to be sterile. This increases the fertility of the males a bit.

The way tetracycline inhibits the sterilization of Oxitec GE mosquitoes.

There is an issue here though, this assumes that the tetracycline would be present in high enough levels to increase fertility, the level needed for this has been empirically determined. Unfortunately for the CT, the levels of tetracycline compounds would need to be 746 to 2500 times greater than the highest reported environmental levels of tetracycline compounds.

Another issue that I haven't brought up is there are two Aedes mosquitoes in Brazil that are of concern, the aforementioned Aedes aegypti and a relative, Aedes albopictus. Although it hasn't been demonstrated to be a vector, A. albopictus populations (I'll have another blog post on this soon) would not be impacted by sterile A. aegypti males. So with two potential vector species (there may be more but that is another blog post), it's not likely that failing to fully knock out ones that escaped the field trial would increase the spread of a virus.

One last point here, I also came across another GE mosquito CT that Bill Gates was spreading Zika virus with the GE mosquitoes. This is crazy because the GE mosquitoes are male and male mosquitoes don't bite. To release something they don't have approval for would be the end of a small company like Oxitec.

The final CT I will discuss, is the claim that the Tdap vaccine is what is causing the microcephaly. This runs the gambit from tainted vaccine to just regular old vaccine and it is harder to address. The basis for this idea is that the Zika virus was discovered in 1947 and there have been no records of microcephaly until the outbreak in Brazil. There are several problems with this idea. The first is that Zika virus was a rare virus in humans until very recently. Also, further analysis of the outbreak in French Polynesia has shown an increase in neurological defects in babies during that time. Another problem is that the Tdap vaccine has never been associated with microcephaly and Brazil has had a 20-fold increase in cases since the outbreak began. They are also suggesting the wrong vaccine if they'd like a chance of being plausible with the CT. Rubella is another virus that causes microcephaly (27% chance if infection occurs in the first trimester), so the MMR vaccine would be the logical choice. 

So in summation, please don't trust everything you read on the internet. Some of it may be the insane ramblings of someone on Reddit, or it might be scare tactics to try and further an agenda.