A resident volunteer put up the posters in an elevator of a public housing estate in the Zika cluster in Singapore
(Copyright Reuters 2016)
CHICAGO/BANGKOK – Zika rampage last year in Brazil caused an explosion of infections, and brought a paralytic neurological abnormality with thousands of babies – an effect that has never seen a mosquito-borne virus.
It is also a mystery: why had a virus, that was little more than a footnote in the annals of infectious diseases taken such a devastating turn in America? How did Africa and Asia, where Zika had quietly circulated for decades, escaped with no reports of large outbreaks or severe complications?
Scientists in the first instance, a theory that Zika the long term in Africa and Asia have granted widespread immunity. Or, perhaps older tribes were less sharp than the linked in Brazil, more than 2,100 cases of microcephaly, a congenital abnormality that is characterised arrested by the development of the brain.
Now, in the midst of the outbreaks in Singapore, Thailand, Vietnam and other parts of Southeast Asia, a much more serious explanation is taking shape: perhaps the threat is there all along, but neurological complications simply escaped official notice.
The question is the control of various research teams, according to leading infectious disease experts and public health officials.
The answer is of immediate relevance for Asia, the region most affected by Zika after the America’s. Thailand is the hardest hit, with more than 680 reported Zika infections this year, followed by Singapore with more than 450, and Vietnam with 60.
Many of the inhabitants live in the so-called “dengue belt’, where the mosquito-borne diseases are prevalent. And vulnerable countries – including Vietnam, the Philippines, Pakistan and Bangladesh are poorly prepared to handle an outbreak with serious consequences, experts said.
Missing a proof of a different degree of virulence, public health officials have warned Asian leaders to prepare for the worst. The scientific community is the following similar assumptions.
“Zika is Zika until the contrary is proven. We assume that all Zikas are equally dangerous,” said Dr. Derek Collector, a biomedical expert at Lancaster University in the Uk.
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The World Health Organization recognizes two main lines of Zika. The first originated in Africa, where it was discovered in 1947 and has not been identified outside the continent. The Asian lineage contains strains that have been reported in Asia, the Western Pacific, Cabo Verde and, in particular, in south America, including Brazil.
The Asian lineage was first isolated in the 1960s in mosquitoes in Malaysia. But some studies suggest that the virus is infecting people since the 1950’s. In the late 1970s, seven cases of human infection in Indonesia were reported.
The first record of a widespread outbreak was in 2007 in Micronesia the Island of Yap.
Experts began to suspect a link to birth defects 2013 during an outbreak in French Polynesia when doctors reported eight cases of microcephaly, and 11 other cases of fetal malformations.
In 2015, it hit Brazil, which peaks in a variety of neurological birth defects, is now called congenital Zika virus syndrome, as well as the Guillain-Barré syndrome, a neurological condition that can lead to temporary paralysis.
Viruses mutate fast, which can lead to strains that are more infectious and more virulent. Many researchers have theorized early on that the devastation in Brazil was caused by an Asian strain that had mutated dramatically.
That theory is based, among other things, on the lack of Zika related to microcephaly in Asia. So if Zika broke out in parts of Asia earlier this year, the researchers were on the lookout.
If researchers were to connect a case of microcephaly an older Asian tribe – and not one that boomeranged back from Brazil — it would debunk the beginning of the theory. It would mean Zika “‘t mutate in a microcephaly caused variant as it crossed the Pacific ocean,” the Collector said.
At least three microcephaly cases have been identified in Asia, but the verdict is still out.
For two microcephaly cases in Thailand, public health officials could not determine whether the mothers had an older Asian strain of Zika or a newer returned from America, said Dr. Boris Pavlin, WHO is acting Zika incident manager for a final briefing.
In Vietnam, where there have been no reports of imported Zika infection, officials are investigating a third case of microcephaly. If it is linked to Zika, Pavlin said that it would suggest that the older strains can cause, microcephaly and, perhaps, the Guillain-Barré.
In Malaysia, where at least six cases of Zika infection have been reported, the authorities have identified both an older South-east Asian tribe, and a similar with the voltage in the Americas, suggesting the possibility that the tribes of both regions are in circulation in some countries.
The yacht is in Africa. In Guinea-Bissau, five microcephaly cases are examined to determine whether the African origin of Zika may lead to microcephaly.
It is a top research priority by the WHO, said Dr Peter Salama, executive director of the agency in emergencies program, in a press conference Tuesday.
“That is a crucial question, because it really has public health implication for African or Asian countries that Zika virus transmission,” Salama said. “We are all following this very closely.”
Scientists are also trying to learn whether the people in places where Zika is endemic are protected by the “herd immunity.” The phenomenon limited the spread of the virus if there is enough of the population is immunized against infection by means of vaccination, previous exposure, or both.
Experts believe that Zika moved explosively in America, because there was no previous exposure. It is not clear how widely Zika has spread in Africa and Asia, or there are pockets of natural immunity – and, more importantly, whether immunity against one strain would provide immunity to the other.
A recent review of studies suggests 15 percent to 40 percent of the population in some African and Asian countries may have been previously infected with Zika, said Alessandro Vespignani, a professor of medical sciences at the Northeastern University in Boston.
That is far below the 80 percent of the population immunity is a mosquito-borne virus expert, estimated in the journal Science would be needed, to block Zika.
Researchers believe that it is possible that the microcephaly went unnoticed in parts of Asia and Africa, where birth defects were not properly tracked.
Also surveyed, said Dr. David Heymann, Chairman of the WHO Emergency Committee, during a press conference last week.
“Now,” he said, “countries are beginning to look back in their records to show on their records what the levels of microcephaly.”