India confirms 80 cases of Zika, 22 pregnant women
Why it’s hard to diagnose Zika
NEW DELHI, Oct 17, (Agencies): India has reported an outbreak of the Zika virus with 80 confirmed cases since last month including 22 pregnant women in the western state of Rajasthan, officials said Wednesday.
India, where the Aedes aegypti mosquito which carries Zika and other viruses is widely prevalent, reported its first Zika cases in January 2017 in neighbouring Gujarat.
Since Zika erupted on a large scale in 2015, more than 1.5 million people in more than 70 countries have been infected, with most in South America.
Awareness
In rare cases, if pregnant women contract the virus their babies can develop brain defects.
In Rajasthan’s capital Jaipur, 330 special teams have been spraying and fumigating houses and almost 440,000 people are under surveillance. “Awareness is key in controlling vector borne diseases. No stone should be left unturned to reach out to the people,” Indian Health Minister J P Nadda said in a statement.
Zika was also detected in the southern Indian state of Tamil Nadu in July 2017. The World Health Organization has said no vaccine is likely to be available until 2020.
When a Zika epidemic was at its height in the Americas two years ago, diagnostics makers began working feverishly to create diagnostic tests for a virus that few in the US had heard of.
Those efforts have now largely stalled, as public concern has waned, health experts say, and the development of inexpensive tests that can quickly detect Zika infections and distinguish them from similar mosquito-borne diseases remains elusive.
A lack of testing capacity has hampered efforts to track Zika in Angola, where a largely unreported cluster of microcephaly cases has been linked to the virus, and left mothers vulnerable to an illness that can cause severe birth defects in developing fetuses.
The best and easiest way to detect a Zika infection is to test for the virus while a person is still symptomatic. This is done through molecular tests, such as polymerase chain reaction or PCR, which look for genetic material from the virus. Such tests have a very short window and must be done during the seven to 14 days when the virus is active. Given that Zika typically causes only mild illness, or no symptoms at all, many people who have been infected miss this critical window.
After the acute infection passes, doctors use so-called serology tests, which sample blood or plasma for antibodies produced in response to the virus.
The drawback with these tests is that Zika is very similar to dengue and other viruses in the same family that are also endemic to tropical regions. Antibodies made in response to these infections can cross-react, producing false positive results.
Because of the potential for cross-reactivity, positive serology results are tested again with a more sensitive, confirmatory test called a plaque reduction neutralization test or PRNT. Such tests are laborintensive and only performed by select public health laboratories.
Dr Eve Lackritz, who leads the Zika Task Force at the World Health Organization, says promoting better diagnostics is a top priority to help track the spread of the virus and develop vaccines. WHO convened a meeting on diagnostics in Geneva last week with global public health officials, test makers and funding agencies.
“This is not the time to step away,” Lackritz said in an interview. “We will see growing populations of susceptible people who can get infected.”
Better tests are needed to check women, especially those who are asymptomatic, during pregnancy, she said. That would include tests to distinguish Zika from other, similar viruses. Another need is for quick, inexpensive tests that could be used easily in a doctor’s office in developing countries.
Nearly two dozen manufacturers responded to WHO’s call in 2016 to develop Zika tests. By 2017, the US Food and Drug Administration had granted special emergency use approval to 19 diagnostic tests.
The designation allowed companies such as Quest Diagnostics, Chembio Diagnostics, Luminex Corp, Siemens Healthineers, Abbott Molecular, and InBios International to sell their tests without a full review of their effectiveness.
“They got to a certain point, but didn’t get actual regulatory approval,” said Maurine Murtagh, a former director of diagnostic services for the Clinton Health Access Initiative. The absence of a large outbreak and waning support from funding agencies has removed a lot of the incentive for companies to press on, she said.