Spatial Association Between a Nipah Virus Outbreak in India and Nipah Virus Infection in Pteropus Bats

To the Editor—Outbreaks of Nipah virus (NiV) have been reported from Malaysia, Singapore, Bangladesh, the Philippines, and India. Pteropid fruit bats are the primary reservoir. Approximately 250 million people are at risk of exposure in outbreak-prone areas of Bangladesh and India [1, 2]. Aerosol transmission, human-to-human spread, high mortality rate, and absence of efficacious vaccines and drugs make NiV a priority pathogen [1]. On 20 May 2018, the Kerala state government, India, declared an outbreak of NiV in the Kozhikode district [3]. Total 23 Nipah cases were identified, including the index (not laboratory confirmed), 18 confirmed, and 4 probable cases [3]. To determine whether Pteropus bats in the neighborhoods (0.5–12 km) of Pallikunnu (Sooppikada–Jumamasjith) and Kadiyankad, near the town of Perambra where the index case lived, were a potential source of zoonosis, throat and rectal samples of 52 Pteropus medius bats were collected and screened by real-time reverse-transcription polymerase chain reaction [4]. The authorities did not allow an on-site necropsy. Nineteen percent of samples tested positive (throat, 15% and rectal swab, 8%; Table 1). The relatively high proportion of Pteropus bats that tested positive for NiV in throat samples of bats in the outbreak area suggests a possible link to the initiation of the outbreak. Nipah Virus Screening in Pteropus medius Bats Collected From Kozhikode District, Kerala (Trapped During 28 May–4 June 2018) Abbreviations: CI, confidence interval; Ct, cycle threshold; NiV, Nipah virus; RT-PCR, reverse-transcription polymerase chain reaction. aCIs drawn on Ct values assuming a normal distribution of the sample. bThe neighborhoods of Pallikunnu (Sooppikada–Jumamasjith) and Kadiyankad. Nipah Virus Screening in Pteropus medius Bats Collected From Kozhikode District, Kerala (Trapped During 28 May–4 June 2018) Abbreviations: CI, confidence interval; Ct, cycle threshold; NiV, Nipah virus; RT-PCR, reverse-transcription polymerase chain reaction. aCIs drawn on Ct values assuming a normal distribution of the sample. bThe neighborhoods of Pallikunnu (Sooppikada–Jumamasjith) and Kadiyankad. Previously, India has witnessed 2 NiV outbreaks, one in the Siliguri district (2001) and the other in the Nadia (2007) district of West Bengal, and the transmission routes proposed among people were close physical contact, exposure to body fluids/respiratory secretions, or contaminated surfaces [5–7]. Earlier studies conducted in 2015 in the North Eastern Region (NER) of India had shown the circulation of NiV in Pteropus bats with 8% positivity [8]. The percentage of NiV-positive bats reported in this study is higher than that previously reported; however, performing a population-based study on bats during an outbreak is difficult. The current outbreak is distinct from prior outbreaks in Malaysia, Bangladesh, and India. In Malaysia, pigs were the intermediate hosts as organized infected piggeries led to pig-to-human transmission. In Bangladesh, ingestion of date palm sap contaminated with infected bat secretions was the main proposed spillover route, followed by person-to-person transmission [9]. In Kerala, sap consumption is not a likely route of transmission; other wildlife–human interactions are more likely to be how transmission occurred (eg, direct handling of bats or items contaminated by bats). The high positivity of NiV in our study detected in bat throat swabs, together with the persistence of virus for a couple of hours on contaminated fruits, enhances the chances of human infection [10]. NiV positivity in bats from NER states and Kerala suggests the possibility of a wider circulation of NiV in other parts of the country as well [4]. To confirm these findings, additional studies including a sampling of bat blood and performing necropsies would be required, but we were unable to achieve this because of panic in the community. Active surveillance efforts for NiV in Pteropus bats are currently under way in India. To minimize the risk of zoonotic transmission, public health authorities should inform the at-risk population that they should not consume partially eaten fruits, as these may be contaminated with NiV during bat feeding. Financial support. The Indian Council of Medical Research–National Institute of Virology, Pune, India, provided financial support to complete this investigation. Potential conflicts of interest. All authors: No reported conflicts of interest. All authors have submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Conflicts that the editors consider relevant to the content of the manuscript have been disclosed.