Zika virus cases detected in India: All you need to know about the mosquito-borne disease

The Zika virus — the latest health scare to grip the planet — created flutters in India as three new cases were detected in Ahmedabad in India.

The virus, although discovered in 1947 in the forests of Uganda, came to prominence in 2015 when pregnant Brazilian women infected with the virus gave birth to babies with abnormally small heads that are normally associated with incomplete brain development (also called microcephaly). It was later linked to another debilitating condition Guillain–Barré syndrome, in which the immune system attacks healthy nerve cells in your peripheral nervous system, that can even lead to paralysis.

What made Zika virus scarier was it’s rather mild symptoms for which people often never seek medical attention, hence are prone to go undetected.

Some scientific papers have concluded that there was a lag of six to 12 months between Zika’s arrival and its detection in Brazil in 2015 and other parts of South America.

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The disease is spread by daytime-active Aedes mosquitoes, the same that spreads dengue and chickangunya. Most people infected with Zika don’t get sick. It can cause a mild illness, with fever, rash and joint pain. But infection during pregnancy can lead to severe brain-related birth defects in babies. It is characterised by brain damage and may cause other defects like blindness, deafness, and even seizures.

What do we know about the virus?

First in Africa: Aedes aegypti is a small, dark, hot-weather mosquito with white markings and banded legs. Scientists believe the species originated in Africa, but came to the Americas on slave ships. It’s continued to spread through shipping and airplanes. Now it’s found through much of the world, including the southern United States.

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Once yellow fever mosquito: Early in the 20th century, scientists showed it was the engine behind devastating yellow fever outbreaks. It became known as the yellow fever mosquito, although that name has been used less often since a successful vaccine was developed against yellow fever. Since then, it’s also been identified as a carrier for other tropical illnesses such as dengue fever, chikungunya and Zika fever. Scientists are investigating whether other types of mosquitoes are spreading Zika in Latin America and the Caribbean, too.

A city-dweller: Aedes aegypti is the primary spreader of Zika and some other tropical diseases, largely because of its unusually cozy relationship with people. While other species thrive in more rural areas, or at least in parks and gardens, this is a domesticated species - sort of a housecat mosquito - accustomed to living in apartment buildings and city centers. It prefers biting people to animals and likes to feed indoors, during daylight hours. Also, it is a hardy bug that can be particularly challenging to get rid of.

Killed off, but it came back: In the early 20th century, many countries developed programs to destroy all Aedes aegypti mosquitoes through spraying chemicals and other measures. By 1970, it was eradicated from much of South America — including Brazil. But many mosquito-control programs were cut back. Reasons included budget cuts, and concerns about the use of some insecticides, and the yellow fever vaccine made the mosquito’s elimination less critical. The species roared back. It played a key role in the reemergence of dengue fever in Latin America and the Caribbean, and the recent spread of chikungunya and Zika virus.

Going for blood: Female mosquitoes drink human blood for nutrients used in making eggs. After a female bites an infected person, it can spread the virus through its saliva to its next human victim. Some scientists think Zika may have arrived in Brazil in 2014, carried by visitors attending World Cup soccer games. Perhaps one or more infected visitors were bitten by mosquitoes and started the chain reaction, said Jeffrey Powell, a Yale University mosquito expert who works in Brazil.

India has been free of this virus for over 60 years, and that traces of Zika were last seen in 1952-53.  The risk of further spread of Zika virus to areas where the competent vectors, the aedes mosquitoes, are present is significant given the wide geographical distribution of these mosquitoes in various regions of the world. Those infected with the virus may have mild fever, skin rash, conjunctivitis, muscle and joint pain or headache. These symptoms normally last for 2-7 days. While countries in the Caribbean are worst hit by the disease, a large number of cases have been reported from South and Central America.

India has strengthened its surveillance system in the past few years to detect and contain new infections. Only three Zika cases have been detected in around 50,000 tested so far, a senior Health Ministry official said.

Between 10 to 16 February in 2016, a total 93 blood samples were collected at BJ Medical College (BJMC) out of which one sample from a 64-year-old male had tested positive for Zika virus.

“This was first Zika positive case reported through AFI surveillance from Gujarat,” the statement said. However, what raises concern is that the second victim of the virus was a 34-year-old woman, who had just delivered a baby.  She had no history of fever during pregnancy and

had no history of travel for three months.

A sample from the patient was referred to the Viral Research and Diagnostic Laboratory (VRDL) for dengue testing and was found to be positive for the virus.

With inputs from agencies