After 60 years of Zika in Asia, why worry?

Zika has been in Asia and the Pacific for at least 60 years, though its mostly mild symptoms have prompted little cause for concern. But with the World Health Organization declaring a global emergency after an outbreak in Brazil that's been linked to serious birth defects, some countries in the region are taking special precautions.

Tonga has declared an epidemic, and the government of the Cook Islands has advised women to delay becoming pregnant. Japan, South Korea, Nepal and India have issued advisories to pregnant women against travelling to infected countries.

South Korea has announced a fine of two million won (about $1,700) on doctors who fail to immediately report suspected cases, while Malaysia has asked travellers to the country to report to health centres if they have symptoms.

Nepal is trying to get rid of any standing water where the Aedes mosquito, which carries the Zika virus, can easily breed, said Dr. Babu Ram Marasini, director of the disease control division at the Department of Health Services.

“We carry out search and destroy campaigns, and request people to throw the water from external containers and dry them out for a few hours,” he said.

India has set up a technical group to monitor the situation, posted warnings at international airports and has promised to ramp up community awareness to stop mosquito breeding.

Although no cases of infection have ever been documented in India, it was in that country, back in 1953, where the first evidence emerged that Zika had jumped from animals to humans. In that study just six years after Zika was discovered in monkeys in Uganda, researchers from the National Institute of Virology, in the city of Pune, found that 33 out of 196 people surveyed had immunity to the virus.

For the most part, symptoms have not been particularly serious, usually a rash and a fever, and little attention was paid to Zika for a long time after the study. But in 2007, Zika exploded in the tiny Pacific island of Yap, in the Federated States of Micronesia, where almost three quarters of its approximately 10,000 inhabitants tested positive.

Six years later, Zika infected about 35,000 people in French Polynesia. It was there that researchers discovered the potential connection between the virus and Guillian-Barré syndrome, according to a 2014 article in Eurosurveillance, a scientific journal that focuses on communicable diseases. Guillian-Barré syndrome causes the immune system to attack the nervous system, leading to a weakening of the limbs and sometimes paralysis.

It is unclear how Zika arrived in Brazil, but researcher published in a US Center for Disease Control journal theorised last year that it may have arrived with participants from Pacific countries at the World Canoeing Championships in Rio de Janeiro in August 2014.

Zika is now spreading rapidly through the Americas after recently showing up first in Brazil, where there have been about 1.5 million cases. Preliminary research appears to show a link between Zika and Guillian-Barré syndrome as well as microcephaly, which can cause babies to be born with small heads and underdeveloped brains.

Despite Zika's relatively benign history in Asia and the Pacific, there is risk that a stronger form of the virus may have emerged, and that it could spread throughout the region with much more severe consequences than previous outbreaks.

"The strain in Brazil could be new because mutation rates in these viruses are high. Moist tropical climates, population explosion and international travel mean Asia is susceptible to Zika," said Dr. Shailendra Saxena, of the Indian Virological Society.

He said that rapidly growing populations in many Asian countries make them vulnerable to an outbreak of Zika. As migration to cities increases, so do slums with poor sanitation and stagnant water where mosquitoes can breed.

nj/jf/ag