Why isn't zika virus causing birth defects in Africa?

[Rick_Kitchen]

If the zika virus originated in Africa, why are the media not reporting cases of birth defects in Africa?

[brickbacon]

I believe the current thinking is that once you get the virus, you are immune to future infections. See here. Since mosquito-borne illnesses are pretty common in many countries in Africa, they suspect that many people were immune to the Zika before they reached an age they might get pregnant. That said, when experts have gone back to look, they have seen other, smaller outbreaks with similar birth defects in children in places like French Polynesia.

If Zika virus has been in Africa and Asia for decades, why wasn’t a link to microcephaly detected earlier?

It may be that the virus never had struck such a large population without immunity.
Microcephaly is rare, and it has many other causes, including infection of the fetus with rubella (German measles), cytomegalovirus or toxoplasmosis; poisoning of the fetus by alcohol, mercury or radiation; or severe maternal malnutrition and diabetes. It is also caused by several gene mutations, including Down syndrome.

Until recently, health officials paid little attention to Zika virus. It circulated in the same regions as dengue and chikungunya, and compared to those two painful infections – nicknamed “break-bone fever” and “bending-up fever” – Zika was usually mild.

The virus is thought to have reached Asia from Africa at least 50 years ago. While it may have caused spikes in microcephaly as it first spread, there was no testing to pin down which of many possible causes was to blame.

In 2007, a Southeast Asian strain of the Zika virus began leap-frogging the South Pacific, sparking rapid outbreaks on islands where no one had immunity to it. Because island populations are small, rare side effects did not occur often enough to be noticed. But in 2013, during an outbreak in French Polynesia, which has 270,000 residents, doctors confirmed 42 cases of Guillain-Barrê syndrome, which can cause paralysis. That was about eight times the normal number and the first hint that Zika virus can attack the nervous system, which includes the brain.

[mozchron]

@brickbacon

I believe the current thinking is that once you get the virus, you are immune to future infections. See here. Since mosquito-borne illnesses are pretty common in many countries in Africa, they suspect that many people were immune to the Zika before they reached an age they might get pregnant. That said, when experts have gone back to look, they have seen other, smaller outbreaks with similar birth defects in children in places like French Polynesia.

We’re not sure, as we don’t have a lot of data, but likely combo of several factors.

(this is assuming of course that the Zika microcephaly link is real, which is not fully clear yet, but for purposes here I’m going to assume its real).

1. In historical Zika endemic areas, people have generally been infected when they are young, and have sterilizing immunity to the virus. By the time they are old enought to get pregnant, most women are immune.

2. Outbreaks were much smaller, giving less of a chance to see microcephaly (in the majority of cases the baby will be OK).

3. It does cause microcephaly, but the link was never recognized, either because of misdiagnosis or simply because no one made the connection due to in general life being difficult.

[lazybratsche]

Another hypothesis posits that people with prior infections of related viruses like dengue have a large but ineffective immune response to Zika. The antibodies that bind to dengue also cross-react with Zika, effectively enough to cause a lot of false positives in testing but not effectively enough to confer immunity.

Then, somehow, an active Zika infection and a massive immune response can screw up fetal brain development.

This hypothesis could explain why microcephaly is seen in South America populations but not in regions with endemic Zika.

[AK84]

IIRC, Zika does not cause bad symptoms in most people it infects and deaths are very rare. How established is the link with birth defects and the virus.

[Leo_Bloom]

I’ve wondered about this and other zika issues for a while, and I guess it’s time to catch up. But for here, briefly: same OP, essentially, but with the premise/question: what about zika in men? I’m not even clear on that distinction in pathology.

[Broomstick]

Well, since men can’t be pregnant, pregnancy complications are not a concern for them personally (assuming they’re decent human beings they will, of course, have some concern for others)

MOST people who get zika will have minor or even no symptoms. Possible complications include something as severe as Guillain-Barré syndrome although thank Og that’s rare. Aside from the now well-publicized pregnancy issues, the risks for men are the same as for women.

[Rick_Kitchen]

@Leo_Bloom

I’ve wondered about this and other zika issues for a while, and I guess it’s time to catch up. But for here, briefly: same OP, essentially, but with the premise/question: what about zika in men? I’m not even clear on that distinction in pathology.

There was just a supposed link between sexual contact and a Zika infection, though I’m not sure that’s been proven for sure. A woman who was not infected had sex with a man who was, and she got the infection.

[Broomstick]

Sexual intercourse involves and exchange of body fluids. Any time you have a virus that can camp out in body fluids there’s a risk of sexual transmission. I don’t know why folks are getting their panties in such a twist over this. If you have a head cold and open mouth kiss your partner you risk viral transmission. Ditto for any other fluid exchange or mucus membrane contact.

[Hari_Seldon]

If infection is generally mild and there is as yet no vaccine, why not inject all young girls with the active virus, at least until a vaccine is found?

[snowthx]

@Hari_Seldon

If infection is generally mild and there is as yet no vaccine, why not inject all young girls with the active virus, at least until a vaccine is found?

My understanding is that is what will happen naturally as the virus becomes endemic to the Americas. The reason for the present alarm is that it is new to these two continents. Meanwhile, back in Africa where this virus originated, you don’t see an abnormal number of microcephaly cases, because people build up resistance when they are young. Once people build resistance here, it will become as “dangerous” here as it is there in relation to birth defects.

There are others here who will probably be along shortly to explain this better than me.

[KarlGrenze]

@snowthx

My understanding is that is what will happen naturally as the virus becomes endemic to the Americas. The reason for the present alarm is that it is new to these two continents. Meanwhile, back in Africa where this virus originated, you don’t see an abnormal number of microcephaly cases, because people build up resistance when they are young. Once people build resistance here, it will become as “dangerous” here as it is there in relation to birth defects.

There are others here who will probably be along shortly to explain this better than me.

Basically, yes. There is some possibility of neurological disease in adults ( Guillain Barré), but I would like more confirmation about that, and that disease is not the only thing that can cause it.

In fact, there are worse diseases transmitted by that mosquito which are more endemic, such as dengue. Even chikungunya causes more longterm problems than zika.