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Pyriproxyfen has not been linked decisively to microcephaly, but there may be reason for further research.
To implicate pryiproxyfen there must be a biological plausibility to it, and since it works on systems that mammals, including humans, do not have, that plausibilty is lacking.
"In the end, the most compelling point against pyriproxyfen's role in Brazil's health issues is this: Health officials in the state of Pernambuco, the so-called epicenter of microcephaly, say that in the three cities reporting the most cases — Recife, Jaboatao and Paulista — pyriproxyfen is not in use."
To implicate pryiproxyfen there must be a biological plausibility to it, and since it works on systems that mammals, including humans, do not have, that plausibilty is lacking.
They're studying the link with the pesticide because that's the only other thing that's changed in the environment since the increase in microcephaly in Brazil and because of it's known effects on brain chemistry. The defense is that the dosage was too small to cause the birth defects. Since it was introduced to the drinking water, it also has the chance to build up its toxicity in the body.
Quote:
Pyriproxifen is an analog of juvenile hormone, which corresponds in mammals to regulatory molecules including retinoic acid, a vitamin A metabolite, with which it has cross-reactivity and whose application during development causes microcephaly.
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Moreover, tests of pyriproxyfen by the manufacturer, Sumitomo, widely quoted as giving no evidence for developmental toxicity, actually found some evidence for such an effect, including low brain mass and arhinencephaly—incomplete formation of the anterior cerebral hemispheres—in rat pups. Finally, the pyriproxyfen use in Brazil is unprecedented—it has never before been applied to a water supply on such a scale. Claims that it is not being used in Recife, the epicenter of microcephaly cases, do not distinguish the metropolitan area of Recife, where it is widely used, and the municipality, where it is not. Given this combination of information we strongly recommend that the use of pyriproxyfen in Brazil be suspended pending further investigation.
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Philippe Grandjean, a highly regarded neurodevelopmental toxicologist affiliated with the Harvard School of Public Health, says, “Few pesticides have been properly tested for developmental neurotoxicity. This is unfortunate as pesticides are suspected of causing a silent pandemic of neurotoxicity. In this case the absence of proper toxicological data confuses the search for causes of the reported surge in microcephaly.” While Sumitomo, the manufacturer of pyriproxyfen, claims there is no reason to be concerned, in reviewing their tests Grandjean notes that “an animal test shows possible link to teratogenic effects and smaller skull,” which is a way microcephaly is detected.
They're studying the link with the pesticide because that's the only other thing that's changed in the environment since the increase in microcephaly in Brazil and because of it's known effects on brain chemistry. The defense is that the dosage was too small to cause the birth defects. Since it was introduced to the drinking water, it also has the chance to build up its toxicity in the body.
"A team of WHO scientists recently reviewed data on the toxicology of pyriproxyfen, one of 12 larvicides that WHO recommends to reduce mosquito populations. It found no evidence that the larvicide affects the course of pregnancy or the development of a fetus. The US Environmental Protection Agency and EU investigators reached a similar conclusion when they carried out a separate review of the product.
Larvicides are an important weapon in the public health practitioner’s arsenal. Especially in cities and towns with no piped water, people tend to store drinking water in outdoor containers. These sources of water, as well as standing water that may collect in garbage, flower pots and tyres, serve as ideal breeding grounds for mosquitoes.
Larvicides such as pyriproxyfen are often used in containers where people store water to kill the mosquito in its larval stage. When people drink water from containers that have been treated with pyriproxyfen, they are exposed to the larvicide – but in tiny amounts that do not harm their health. Moreover, 90% - 95% of any larvicide ingested is excreted into the urine within 48 hours. This product has been used since the late-1990s without being linked to microcephaly."
Colombia Is Hit Hard by Zika, but Not by Microcephaly
In Brazil, more than 2,000 babies have been born with microcephaly, abnormally small heads and brain damage caused by the Zika virus. In Colombia, officials had predicted there might be as many as 700 such babies by the end of this year. There have been merely 47.
The gap has been seen all over the Americas. According to the World Health Organization, the United States has 28 cases — almost all linked to women infected elsewhere. Guatemala has 15, and Martinique has 12.
Had the rest of the Americas been as affected as northeastern Brazil, a tidal wave of microcephaly would be washing over the region. Most experts say that will not happen, but they are at a loss as to why.
From back in January: Zika-related microcephaly cases in Brazil were overreported
On Wednesday, Brazil’s Ministry of Health said 4,180 cases of Zika-related microcephaly had been reported since October. The country is trying to find out which cases it could actually confirm from notifications provided by doctors — a slow and complicated process as the information is compiled and checked by health secretariats in 26 states and one federal district spread across South America’s biggest country.
After experts scrutinized 732 of the cases they found that more than half either weren’t microcephaly, or weren’t related to Zika. 270 were confirmed as microcephaly that appears to be linked to Zika or other infectious diseases, according to the latest ministry bulletin.
Colombia Is Hit Hard by Zika, but Not by Microcephaly
In Brazil, more than 2,000 babies have been born with microcephaly, abnormally small heads and brain damage caused by the Zika virus. In Colombia, officials had predicted there might be as many as 700 such babies by the end of this year. There have been merely 47.
The gap has been seen all over the Americas. According to the World Health Organization, the United States has 28 cases — almost all linked to women infected elsewhere. Guatemala has 15, and Martinique has 12.
Had the rest of the Americas been as affected as northeastern Brazil, a tidal wave of microcephaly would be washing over the region. Most experts say that will not happen, but they are at a loss as to why.
From back in January: Zika-related microcephaly cases in Brazil were overreported
On Wednesday, Brazil’s Ministry of Health said 4,180 cases of Zika-related microcephaly had been reported since October. The country is trying to find out which cases it could actually confirm from notifications provided by doctors — a slow and complicated process as the information is compiled and checked by health secretariats in 26 states and one federal district spread across South America’s biggest country.
After experts scrutinized 732 of the cases they found that more than half either weren’t microcephaly, or weren’t related to Zika. 270 were confirmed as microcephaly that appears to be linked to Zika or other infectious diseases, according to the latest ministry bulletin.
Colombia is continuing to monitor pregnancies in which confirmed maternal infection with Zika has occurred. Many are still pregnant, so it's impossible to know yet what the incidence of microcephaly and other anomalies will be and the risk when infection happens in each trimester
No one has ever said that Zika is the only cause of microcephaly.
I am not sure what the purpose of your post is. If it is that you do not think Zika can cause microcephaly and other anomalies that is clearly not true. If it is that the risks are not yet understood, that is true. Researchers are still working on collecting data.
Consider congenital rubella syndrome, where we do have the data.
"Congenital rubella syndrome (CRS) can occur in a developing fetus of a pregnant woman who has contracted rubella, usually in the first trimester. If infection occurs 0–28 days before conception, the infant has a 43% risk of being affected. If the infection occurs 0–12 weeks after conception, the risk increases to 51%. If the infection occurs 13–26 weeks after conception, the risk is 23% of the infant being affected by the disease. Infants are not generally affected if rubella is contracted during the third trimester, or 26–40 weeks after conception."
This shows us that even if infection with rubella happens up to a month before conception there is considerable risk to the fetus, the risk is highest during the first twelve weeks of pregnancy, when organs are forming, and then the risk declines. We also see that not every exposed fetus has birth defects. This is the kind of data that we do not have for Zika. It will be expected that not all exposed babies will have birth defects. It's only been a matter of months since the connection between Zika and microceohaly was suspected. There are too few completed pregnancies with documented infections to be able to provide information like that we have for rubella yet.
No one has ever said that Zika is the only cause of microcephaly.
I am not sure what the purpose of your post is. If it is that you do not think Zika can cause microcephaly and other anomalies that is clearly not true. If it is that the risks are not yet understood, that is true. Researchers are still working on collecting data.
Zika has been around for decades. The hysteria about the purported caucation of microcephaly by the Zika virus is only recent. The information supporting that faulty conclusion was found to be improperly collected in Brazil and was known as far back in January before the media hysteria. Furthermore, several more recent news items in this thread indicate that there've been no significant increase in the birth defect outside that region. The information presented above casts doubt not only on the claims about the Zika virus but the larvicide pyrixproxyfen as well.
Zika has been around for decades. The hysteria about the purported caucation of microcephaly by the Zika virus is only recent. The information supporting that faulty conclusion was found to be improperly collected in Brazil and was known as far back in January before the media hysteria. Furthermore, several more recent news items in this thread indicate that there've been no significant increase in the birth defect outside that region. The information presented above casts doubt not only on the claims about the Zika virus but the larvicide pyrixproxyfen as well.
Since the possible association between Zika and birth defects was onl recently discovered it was not even looked for in the past. There was not even a good test for it. Therefore we have no way of knowing how many cases of microcephaly were caused by Zika before we started looking for it.
That Zika can cause birth defects is now not disputed. It joins a list of other infectious agents that do so, including toxoplasmosis, rubella, and cytomegalovirus.
If you are going to say pyriproxyfen causes birth defects you have to account for the areas where there are Zika infections and birth defects but no use of the larvicide. You also have to account for why the larvicide has been used for several decades with no correlation with any birth defects. Then you have to provide a plausible biological mechanism by which the larvicide could cause birth defects, and there isn't one. Its action is on biologic systems that insects have but mammals, including humans, do not have.
I said it casts doubt on the claims of causation of microcephaly for both Zika and pyriproxyfen. A coincident rise in microcephaly cases with the presence of Zika infections is not showing up anywhere else. In NE Brazil, the microcephaly cases were greatly overreported. Only just over 1 percent of the originally reported microcephaly cases turned out to have been infected with the Zika virus. There is nothing to see here. The data is not supporting the hysteria that has died down since. The public authorities have stopped putting the larvicide in the water supply.
I said it casts doubt on the claims of causation of microcephaly for both Zika and pyriproxyfen. A coincident rise in microcephaly cases with the presence of Zika infections is not showing up anywhere else. In NE Brazil, the microcephaly cases were greatly overreported. Only just over 1 percent of the originally reported microcephaly cases turned out to have been infected with the Zika virus. There is nothing to see here. The data is not supporting the hysteria that has died down since. The public authorities have stopped putting the larvicide in the water supply.
I do not think you read my link describing the evidence that supports Zika causing birth defects. from that link:
"Thus, on the basis of a review of the available evidence, using both criteria that are specific for the evaluation of potential teratogens and the Bradford Hill criteria as frameworks, we suggest that sufficient evidence has accumulated to infer a causal relationship between prenatal Zika virus infection and microcephaly and other severe brain anomalies. Also supportive of a causal relationship is the absence of an alternative explanation; despite the extensive consideration of possible causes, researchers have been unable to identify alternative hypotheses that could explain the increase in cases of microcephaly that were observed first in Brazil and then retrospectively in French Polynesia, and now in preliminary reports that are being investigated in Colombia."
After the association of Zika with birth defects was made in Brazil, researchers looked at a Zika outbreak in French Polynesia two years ago that affected about two thirds of the population. They found 8 cases of microcephaly, about four fold higher than usually expected. Zika infection in the first trimester of pregnancy was statistically associated with microcephaly.
Pyriproxyfen is not even used in French Polynesia:
You continue to ignore the fact that there is jut not enough information yet to know what the risk is to a fetus if exposed in utero. This article addresses that:
"To date, 19 countries and territories in the Americas have reported confirmed cases of congenital syndrome associated with Zika virus infection. Since the Zika Epidemiological Update of 20 October 2016, Bolivia and Trinidad and Tobago have reported confirmed cases of congenital syndrome associated with Zika virus infection.
As of EW 35, Canada reported two maternal-fetal transmissions of Zika Virus; one with severe neurological anomalies."
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