Zika Virus Outbreak in India: A 2024 Update

Overview of the Situation

From January 1 to December 31, 2024, India reported a total of 151 cases of Zika virus disease (ZVD) across three states: Maharashtra, Karnataka, and Gujarat. Maharashtra recorded the highest number of cases, with 140 reported through the Integrated Disease Surveillance Programme (IDSP). Of these, 125 cases were from Pune district, followed by 11 in Ahmednagar, and single cases in Kolhapur, Sangli, Solapur, and Mumbai suburban areas. Karnataka recorded ten cases—seven in Bengaluru Urban and three in Shivamogga—while Gujarat reported one case in Gandhinagar.

The rise in Zika cases in Maharashtra is significant, marking the highest number of cases reported since 2021. Comparatively, the state reported only one case in 2021, three in 2022, and 18 in 2023. Karnataka, too, saw its highest count since its first recorded case in 2022. Notably, no cases of microcephaly or Guillain-Barré syndrome (GBS) linked to the outbreak have been reported as of December 31, 2024.

Understanding the Zika Virus

Zika virus (ZIKV) is primarily transmitted through the bite of infected Aedes mosquitoes, notably Aedes aegypti and Aedes albopictus. It can also be transmitted from mother to fetus during pregnancy, as well as through sexual contact, blood transfusions, and possibly organ transplantation.

First identified in Uganda in 1947 in a Rhesus macaque, the virus was later found to infect humans in the 1950s. While most infections are asymptomatic or mild, severe complications can occur, particularly in pregnant women. Infection during pregnancy is linked to microcephaly and congenital Zika syndrome (CZS), while in rare cases, adults and children may develop neurological disorders such as GBS, neuropathy, and myelitis.

Public Health Response

On July 3, 2024, the Government of India issued an advisory to all states following the ZVD outbreak in Maharashtra. The response measures included:

• Strengthening surveillance through IDSP, which monitors over 40 communicable diseases, including ZVD.
• Utilizing designated laboratories, such as District Public Health Laboratories and State Referral Laboratories, for disease investigation.
• Disseminating technical guidelines for integrated vector management and ensuring community participation in mosquito control measures.
• Providing financial support to states under the National Health Mission for preventive activities, including domestic breeding checks, insecticide distribution, fogging, training, and awareness campaigns.
• Intensified active surveillance in Maharashtra, particularly focusing on pregnant women. Close monitoring of ZIKV-positive pregnancies was conducted, and vector control measures were enhanced in affected areas.

WHO Risk Assessment

The World Health Organization (WHO) warns that ZIKV can cause large outbreaks, particularly when introduced to populations with no prior immunity. Given the widespread presence of Aedes mosquitoes in India, particularly during the monsoon and post-monsoon seasons, the risk of further transmission remains high.

Since India’s first reported Zika case in Gujarat in 2016, multiple states, including Tamil Nadu, Madhya Pradesh, Rajasthan, Kerala, Uttar Pradesh, Delhi, and Karnataka, have reported cases. However, no cases of Zika-related microcephaly have been recorded in India to date. The higher-than-usual number of cases in Maharashtra in 2024 suggests underreporting in previous years due to asymptomatic or mild infections and variable clinician awareness.

Preventive Measures and WHO Advice

Mosquito Control and Personal Protection

Preventing mosquito bites remains the primary method to avoid Zika infection. WHO advises:

• Eliminating mosquito breeding sites by covering water storage containers, removing stagnant water, and cleaning potential breeding spots such as flowerpots, discarded tires, and trash.
• Community-driven efforts to support public health initiatives in reducing mosquito populations.
• Use of larvicides and insecticides in high-risk areas.
• Wearing long-sleeved clothing, using insect repellent containing DEET, IR3535, or Icaridin, and ensuring living spaces have mosquito screens.

Sexual Transmission and Pregnancy Precautions

Since Zika can be transmitted sexually, individuals in Zika-affected areas, especially pregnant women, should take extra precautions:

• Pregnant women should practice safe sex (consistent condom use) or abstain from sexual activity throughout pregnancy.
• Couples who have traveled to areas with active Zika transmission should use condoms or abstain from sex for three months (for men) and two months (for women) to prevent sexual transmission.
• Women concerned about unprotected sex and potential pregnancy should have access to emergency contraception and counseling.
• Enhanced prenatal care, including regular ultrasound monitoring, should be encouraged for pregnant women in affected areas.

No Travel or Trade Restrictions

WHO does not recommend any travel or trade restrictions to India based on the current situation. However, travelers should take necessary precautions to prevent mosquito bites, particularly pregnant women and those planning to conceive.

Conclusion

The 2024 Zika virus outbreak in India highlights the need for sustained vector control, improved surveillance, and public awareness. While the number of cases has risen significantly in Maharashtra and Karnataka, the absence of reported microcephaly or GBS cases is reassuring. However, given the virus’s potential to cause severe birth defects and neurological disorders, continued vigilance is necessary. Public cooperation in eliminating mosquito breeding grounds, using protective measures, and adhering to WHO guidelines will be key to controlling the spread of ZVD in India.