Unless you’ve been hiding under a rock, you’ll have seen news stories about a zika virus epidemic in Brazil. Unless you study viruses for a living, you’ve probably never heard of this little bugger.
It was first recognised in a rhesus monkey hung in a cage in a tree in the Zika forest of Uganda in 1947. What were people doing hanging caged monkeys in trees in Uganda? They were studying Yellow Fever and trying to cause a natural infection in the poor beast; but they ended up catching something nobody had ever seen before.
Zika belongs to the same virus family as Yellow Fever and if you travel to some parts of the world a Yellow Fever vaccination is a pretty good idea. In those parts, including large parts of Africa and Latin America, Yellow Fever kills 30,000 people a year.
In combination with malaria, which is from a very different family but has some similar symptoms, yellow fever managed to kill 22,000 people and stop the French completing the Panama Canal in 1889.
The Americans eventually succeeded in building the canal by realising that mosquito control was the key. In those days, working out ‘what causes what’ was even harder than today, so it required a leap of faith to invest in mosquito control when no-one really knew they were the cause of the problems; the fact that it worked was pretty good evidence!
Unlike Yellow Fever, Zika rarely, if ever, kills. According to the US Centre for Disease Control (CDC), 4 out of 5 people who catch Zika never even know they’ve had it. But this outbreak has sparked major international interest by being linked to a simultaneous spike in the rate of microcephaly in Brazil.
This rise has been quite extraordinary with over 3,500 cases having been found in recent months; compared with 146 in the whole of 2014.
I mentioned microcephaly in a previous article on New Matilda; 30 cases of microcephaly is the full extent of the birth defects due to the large and rapid radiation doses received by survivors of the 1945 atomic bombings of Hiroshima and Nagasaki.
The word microcephaly means ‘small head’ and that’s what it is. Children are born with a smaller than usual head and brain. The impact can range from mild and hardly noticeable to severe. With radiation induced microcephaly, it was discovered that women had to be hit with more than a specific level of radiation at a critical period of the pregnancy. Women hit with much larger doses before or after this critical period had normal children.
With Zika, nobody yet knows if there is a critical period and it will be hard to find this because most of the women will not have known they even had Zika, let alone when they got it.
But what exactly does the recent figure of 3,500 affected children mean? In South Australia (population 1.6 million), we generally get about 10 children with microcephaly per year. If Brazil had a similar rate, given her population of 200 million, then she’d get about 1,200 cases per annum, so the reported 147 cases in 2014 shows that her normal rate is either very low or there is substantial under-reporting.
Under reporting is entirely plausible – this isn’t like being born with 12 fingers or two heads. Many children with heads on the small side of the normal distribution may simply not have been noticed. But now that everybody is out with a tape measure, we would expect a more accurate figure. This will, however, make it difficult to separate any change in the actual rate from a change in the measurement practices.
But how has the link been made between this usually insignificant virus and this frequently tragic birth defect?
First, the rate spike was noticed. This was originally reported as a rough doubling of numbers late in 2015. Once people were alert, the doubling grew into more like a 20 fold increase.
The second piece of evidence is because the virus has been found in the blood of some of the children. Obviously somebody thought a link was plausible, or they wouldn’t have tested for the virus in the children in the first place.
Experts think there’s enough evidence for a tentative link, but the next few years will see a flurry of research aimed at finding out exactly what is happening.
As I write you can bet that labs all over the planet will be sequencing the RNA of this virus. And note that I said RNA and not DNA.
Zika is from a class called single stranded RNA viruses. This class has a particularly rapid rate of evolution because RNA is a little less stable than DNA and not having a double stranded genome means these little buggers lack good repair mechanisms for handling replication errors.
In English, this just means that every outbreak is different, some are cruel and some relatively benign. This one is looking particularly cruel.
The WHO has now convened an emergency committee and is prioritising vaccine development and improvements to diagnostic testing. Many viruses have what is called a reservoir host, an animal in whom they circulate without causing serious illness. They then spillover into humans in response to some event.
Where was Zika before Brazil’s first case in May 2015? Where had it been living since the last outbreak?
In the case of Ebola, it is suspected that the virus lives in bats and only infects people after they eat chimps, gorillas, antelope or porcupines who have been infected; bush meat may come with karma.
It is normal after an outbreak for virus hunters to catch, kill and blood sample thousands of native animals in their search for a reservoir. In these more enlightened times, samples may be taken without killing the animals.
Everybody on the planet has to be hoping that the microcephaly jump is due to something else. The prospect of a largely symptomless virus having mutated into something which can have such a tragic impact is truly horrifying.
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