On 8 July 2021, a Zika virus (ZIKV) infection was laboratory-confirmed in a resident of Kerala state, south-west India. This represents the first Zika virus disease case ever reported from Kerala. ZIKV viral RNA was detected through RT-PCR testing at the National Institute of Virology (NIV) Pune, in a blood sample collected from the patient, a 24-year-old pregnant woman in her third trimester of pregnancy resident in Trivandrum district. On 28 June 2021, she was admitted to a private hospital with arbovirus like symptoms of fever, headache and general rash. Laboratory results were negative for dengue virus (DENV) and chikungunya virus (CHIKV). The woman delivered on 7 July, she was reportedly in good health and there were no apparent birth defects in the new-born. In the 3 months before delivery, she had resided in Trivandrum district not having traveled during that period. Among her close contacts, her mother reported having fever and similar symptoms one week before ZIKV confirmation in her daughter.
Retrospective testing was conducted among 19 hospital staff and patients at the same private hospital who had previously presented with fever, myalgia, arthralgia and petechial lesions in May 2021. Blood samples collected from these 19 ZIKV suspected cases were sent to NIV Pune, and on 10 July the laboratory results confirmed that 13 of the 19 samples tested positive for ZIKV by RT-PCR, indicating cryptic transmission of ZIKV in Kerala state since May 2021.
During the period from 8 to 26 July 2021, 590 blood samples were collected in Kerala state through active case finding and passive surveillance. Of them, 70 (11.9%) tested positive for ZIKV by RT-PCR at NIV Pune, including four additional pregnant women. All these cases were from Trivandrum district, except two cases reported from Ernakulam and Kottayam districts, who both had recent travel history to Trivandrum district.
On 31 July 2021, Maharashtra state also reported its first Zika laboratory-confirmed case from Belsar, a village of 3500 inhabitants located in Purandar Taluka administrative unit, Pune district. The case, a 50-year-old women, tested positive for both ZIKV (by RT-PCR and sero-neutralization) and CHIKV (by RT- PCR and IgM ELISA) at NIV Pune. Fifty-one additional samples from ZIKV suspected cases were collected from Belsar village, of them 40 tested negative for ZIKV and 11 are still pending for results.
So far, no cases of microcephaly and/or Guillain-Barre syndrome (GBS) have been linked with this outbreak.
Public health response
The Kerala Health department, along with local self-government health departments has implemented the following response activities:
On 8 July 2021, the State of Kerala issued guidelines on enhanced surveillance for ZIKV disease and sent guidance to all 14 districts.
Information, Education and Communication activities pertaining to ZIKV disease have been strengthened immediately throughout the State. Sensitization activities across the State for both health care workers and the general public are ongoing.
All ultrasound scanning centers have been directed to report incidences of microcephaly during regular antenatal scans to the Reproductive and Child Health Officer.
Currently, four laboratories (National Institute of Virology Alappuzha, Medical College laboratories of Trivandrum, Thrissur and Kozhikode) in Kerala state are equipped to perform RT-PCR testing for ZIKV infection. The State is also planning to start testing in another public health laboratory in Trivandrum district. So far, the State has received 2100 RT-PCR kits from NIV Pune to detect Zika cases, which have been distributed to the four laboratories mentioned above.
Measures to ensure strict deferral of blood donors with a history of fever in the previous two weeks, have been undertaken.
A central team visited the Trivandrum district and collected samples of mosquitoes and larvae from the residential area of the cases and sent them for testing at the Vector Control Research centre, Kottayam field station in Kerala state. The results are pending.
The State Health Minister has conducted multiple rounds of reviews, and all the districts have been alerted to carry out active surveillance, mosquito control and information, education, and communication activities related to control of ZIKV.
In Trivandrum district, which has been declared as having a cluster of ZIKV disease cases, intensified vector control activities have been conducted for a week including; extensive fogging, spraying, use of larvicides, source reduction and sanitization of the surrounding areas. Additionally, field teams visited each household to conduct active case finding, ensure elimination of mosquito breeding sites, and sensitize the community to preventive mosquito control measures and identification of ZIKV disease symptoms to seek timely medical assistance.
WHO was requested to support the country’s updates on standard operating procedures and guidelines for: syndromic and case-based surveillance; laboratory surveillance; vector surveillance; enhanced surveillance among antenatal women; microcephaly surveillance; surveillance of Acute Flaccid Paralysis (AFP) and GBS.
WHO risk assessment
ZIKV can cause large epidemics with a substantial demand on the public health system including surveillance, case management, and laboratory capacity to differentiate ZIKV disease from illness due to co-circulating mosquito-borne viruses like dengue and chikungunya. Although 60-80% of the Zika virus infected cases are asymptomatic or only have mild symptoms, ZIKV can cause microcephaly, congenital Zika syndrome (CZS) and GBS. Moreover, although ZIKV is primarily transmitted by Aedes species mosquitoes, it can also be transmitted from mother to foetus during pregnancy, through sexual contact, transfusion of blood and blood products, and organ transplantation.
In India, ZIKV disease cases/infections have been detected in Gujarat, Madhya Pradesh and Rajasthan states in 2018 (South-East Asian lineage), but no ZIKV-associated microcephaly has been reported. Although this event is not unexpected, given the wide distribution of the primary mosquito vector, Aedes aegypti, and competent vector, Aedes albopictus, in Kerala and Maharashtra states, this is unusual as it is the first time that ZIKV disease cases have been confirmed in these states.
The overall risk is considered low at the regional level and global level, while at the national level (Kerala and Maharashtra States) is currently assessed as moderate, given that:
The actual ZIKV transmission might be higher due to the undetermined population immunity in the two affected states and the asymptomatic clinical presentation in most of the ZIKV infections;
The primary vector Aedes aegypti, and competent vector Aedes albopictus, are established in the area, often in high densities, and the ecological conditions are favourable for ZIKV transmission and potential endemicity;
The current evidence suggests that the main source of infection is due to vector-borne transmission; however, epidemiological and entomological investigations are ongoing and the outbreak magnitude might change;
Although appropriate control measures have been implemented, and travel is currently limited under COVID-19 pandemic conditions, further spread of the disease cannot be excluded through asymptomatic and mildly symptomatic infected persons;
The ongoing monsoon season could increase the vector density and the likelihood of further transmission via mosquitos;
Kerala is a tourist destination with frequent travel to and from other areas of the country and other countries; however, there are current travel restrictions because of the COVID-19 pandemic.
The exportation within India and to other states and countries cannot be ruled out due the presence of competent vector (Ae. aegypti) in other states where mosquitos can become infected by biting infected returning travellers leading to potential further spread of the disease.
The region as a whole remains at risk for ZIKV transmission because of the presence of competent vectors, often in high densities and vector control activities might have been interrupted in other countries because of the pandemic.
WHO advice
Protection against mosquito bites during the day and early evening is a key measure to prevent ZIKV infection. Special attention should be given to the prevention of mosquito bites among pregnant women, women of reproductive age, and young children.
Aedes mosquitoes breed in small collections of water around homes, schools, and workplaces. It is important to eliminate these mosquito breeding sites by appropriate methods, including: covering water storage containers, removing standing water in flower pots, and cleaning up trash and used tires. Community initiatives are essential to support local government and public health programmes to reduce mosquito breeding sites. Health authorities may also advise the use of larvicides and insecticides to reduce mosquito populations and disease spread. Semi-urban areas should prevent the breeding of Aedes spp., in rubber plantations and other stagnant pools of water.
Basic precautions for protection from mosquito bites should be taken by people traveling to high-risk areas, especially pregnant women. These include the use of repellents, wearing light coloured, long-sleeved shirts and pants, ensuring rooms are fitted with screens to prevent mosquitoes from entering.
For regions with active transmission of ZIKV, all persons with suspected ZIKV infection and their sexual partners (particularly pregnant women) should receive information about the risks of sexual transmission of ZIKV.
WHO recommends that sexually active men and women be correctly counselled about ZIKV infection and offered a full range of contraceptive methods to be able to make an informed choice about whether and when to become pregnant in order to prevent congenital Zika syndrome and other possible adverse pregnancy and foetal outcomes.
Women who have had unprotected sex and do not wish to become pregnant due to concerns about ZIKV infection should have ready access to emergency contraceptive services and counselling. Pregnant women should practice safer sex (including correct and consistent use of condoms) or abstain from sexual activity for the entire duration of pregnancy. Pregnant women should be encouraged to attend scheduled appointments and enhanced antenatal care and follow-up, including ultrasound imaging to detect microcephaly and other developmental anomalies associated with ZIKV infection in pregnancy, in accordance with the state/national response plan.
For regions with no active transmission of ZIKV, WHO recommends practicing safer sex or abstinence for a period of six months for men and two months for women who are returning from areas of active ZIKV transmission to prevent infection of their sex partners. Sexual partners of pregnant women, living in or returning from areas where local transmission of ZIKV occurs, should practice safer sex or abstain from sexual activity throughout pregnancy.
About WHO
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