Is Zika a potential threat to India?

Zika virus (ZIKV) is so-called because it was first obtained from an infected rhesus monkey in the Zika forest in Uganda in 1947 (Dick et al. 1952). It was first obtained from infected humans in 1952 in Tanzania and Uganda (Dick 1952).

Humans are commonly infected with ZIKV by the bite of infected mosquitoes, although other modes of transmission such as through blood transfusion or sexual contact have also been reported. Dengue, Japanese encephalitis, Yellow fever and West Nile viruses are closely related to ZIKV.

Most people infected with ZIKV develop mild or no symptoms. Those who do develop symptoms usually exhibit fever, joint pain, muscle pain, rashes, conjunctivitis, and general fatigue. The disease usually resolves by itself within a week.

The major complication of ZIKV infection is microcephaly, where babies are born with abnormally small brains. The virus spreads to babies through infected pregnant mothers.

It is now believed that microcephaly could just be the tip of the iceberg, as it is slowly emerging that other congenital brain abnormalities also occur. Importantly, Guillain-Barré syndrome is another complication that can cause paralysis, and even death.

Where has Zika virus spread so far? The first human outbreak of Zika infection occurred in 2007 in Yap Island, Micronesia, followed by French Polynesia in October 2013, New Caledonia in January 2014 and Cambodia in November 2016 (Grard et al. 2014).

Currently, the Zika outbreak has reached pandemic proportions after spreading to Mexico, Central America, South America, and the Caribbean... The virus has already spread to Southeast Asia. The Center for Disease Control and Prevention (CDC) has so far reported Zika outbreaks from 12 Southeast Asian countries...

Subsequently, CDC issued a travel advisory, cautioning against visiting these Zika-endemic countries. These reports from neighbouring countries have naturally placed India on high alert. As of 2 February 2017, the World Health Organization (WH­O) indicated that the overall risk assessment has not changed as the virus is still spreading to areas where the Aedes vector is present.

Although some countries have reported a decline in the cases of Zika infection, vigilance needs to remain high (WHO, 2017a).

What is the threat to India? ZIKV prevalence has been reported by a single Indian study, way back in 1954 from Maharashtra and Gujarat, where only 17% prevalence of Zika antibodies was evident in the population studied (Smithburn et al. 1954).

However, t­he situation has changed drastic­a­lly since then, with the re-emergence­ of several vector-borne diseases in India. Some of the major fa­­ctors that currently pose a threat to India include the following:

Mosquito vector: Dengue and chikungunya are endemic in India, both of which share the same mosquito vectors (Aedes aegypti and Aedes albopictus) with ZIKV. As of 31 December 2016, India reported 1,11,880 cases of dengue, with 227 deaths (Ministry of Health & Family Welfare, 2016a); 58,136 cases of chikungunya were reported for the same timeframe (Ministry of Health & Family Welfare, 2016b).

Therefore, there is potential for the spread of ZIKV to hitherto-unaffected areas, where these common mosquito vectors are present. Air travel: Air travel has increased dramatically in recent years. During 2016–17 alone, Indian airports had a footfall of 265 million passengers, of which 205.7 million were domestic and 59.3 million were international (Know India, 2017).

With such large number of passengers passing through (and within) India, it is difficult to keep track of people who might possibly be infected with ZIKV. Climate change: Climate change has a major impact on vector dynamics.

Recent evidence indicates that the variation in climatic conditions over the past several decades has directly influenced the spread of vector-borne diseases. WHO estimates that in the next 100 years average global temperatures will rise by 1–3.5°C facilitating the spread of vector-borne diseases to new geographical niches (Githeko et al. 2000).

This will likely increase the geographical range of the Aedes vectors, thereby facilitating the spread of ZIKV, besides other arboviruses such as dengue and chikungunya to new areas (Climate Nexus, 2015).
What can be done? ZIKV poses a real threat to India if adequate corrective measures are not undertaken in a timely manner.

Given the fact that there is currently no specific antiviral agent to treat Zika infections and a Zika vaccine is likely to take several years to be available, the only option is vector control. More intensive, integrated vector control measures such as environmental management, personal protection, biological and chemical control, health education and community mobilisation, and appropriate legislative measures, will help to tackle the problem better.

There is also a need for rigorous surveillance, including detection of ZIKV in mosquitoes. Timely mobilisation of public funds will expedite surveillance operations. Preparedness of public health personnel in the eventuality of an outbreak needs to be ensured. Airports should be kept on high alert for screening possible infected travellers arriving from Zika-endemic countries.

The Government of India has taken a step in the right direction by implementing Rapid Response Teams to track Zika outbreaks (Doss et al. 2017). The recent detection of ZIKV in three patients from Ahmedabad district in Gujarat (WHO, 2017b) has sounded the warning bells and underscores the need for further sustained efforts and greater political will for thwarting the emerging threat of Zika transmission in India. (Reprinted with permission from Ideas for India - www.ideasforindia.in)

By Kaushik Bharati