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Background <p>Kyasanur Forest Disease (KFD) is a zoonotic viral disease caused by the Kyasanur Forest Disease Virus (KFDV), belongs to the family Flaviviridae, and is transmitted to humans through the bites of infected ticks, primarily in forested regions. Thirthahalli taluk from Shivamogga district of Karnataka has been reporting a consistently high burden of KFD. We describe the epidemiology of KFD cases in Thirthahalli taluk, identify high-risk groups, describe tick species and correlate KFD hot-spots with the number of cases.</p> Methods <p>We conducted a retrospective analysis of KFD surveillance data obtained from district surveillance unit, Shivamogga, on human, tick and monkey data, of Thirthahalli taluk from November 2017 to May 2022, described epidemiology, calculated the annual and seasonal time-trend of cases. We described the PHC-wise disease burden. We correlated number of cases with number of tick pools and/ or monkey carcass positive for KFDV and reported Pearson’s correlation coefficient.</p> Results <p>Thirthahalli taluk reported 326 cases, all were lab-confirmed using either RT-PCR (93%) or IgM-ELISA (7%); with an annual incidence rate of 45.9 per 100,000 population, 58% in males and median age 40 (IQR 28–51) years. The case fatality rate was 1.8%. Age groups with the highest average annual incidence were 45 to 49&#xa0;years (8.4 per 100,000 population) and 50–54&#xa0;years (8.1 per 100,000 population). Most (72%) cases occurred from February to April, and in the years 2019 (38%) and 2020 (44%) crossing the outbreak threshold. Among 16 Primary Health Centres (PHCs) under Thirthahalli, the population coming under six PHC reported 84% of cases and all deaths. Among 696 tick pools collected from 2018 to 2022, 31 were positive for KFDV (tick pool positivity 4.5%)&#xa0;and three monkey carcasses were KFDV positive. All identified KFDV-positive ticks belonged to the nymphal stage of the genus <i>Haemaphysalis</i>, and species included <i>H.spinigera</i> (23%), <i>H. leachi</i> (10%), and <i>H. turturis</i> (7%). There was correlation between number of human cases in a PHC and tick pool positivity (r = 0.62); and positive tick pools and positive monkey carcasses (r = 0.71).</p> Conclusion <p>Thirthahalli taluk had an ongoing endemic transmission of KFD during the study period including two outbreaks in consecutive years. Age groups most at risk for the disease were middle-aged adults. All deaths occurred in PHCs with a high case burden. All KFDV-positive ticks belonged to the nymphal stage of the <i>Haemaphysalis</i> genus. Occurrence of human cases per year was moderately correlated with tick pool positivity. We recommend continued tick surveillance and monkey carcass testing to map disease hot-spots; and targeted interventions in high-burden PHCs and at-risk age groups for effective disease control.</p>

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Descriptive epidemiology of Kyasanur forest disease in Thirthahalli taluk, Shivamogga, Karnataka, 2018–2022

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  • 发表日期：

    2025年4月2日

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  • Srividya K. Vedachalam,
  • Bhavesh L. Rajput,
  • Sushma Choudhary,
  • Bhuvaneshwari Arumugam,
  • Ajit D. Shewale,
  • Pallavi D. Mahadevappa,
  • Padma M. Rajagopal,
  • Simmi Tiwari

摘要

Background

Kyasanur Forest Disease (KFD) is a zoonotic viral disease caused by the Kyasanur Forest Disease Virus (KFDV), belongs to the family Flaviviridae, and is transmitted to humans through the bites of infected ticks, primarily in forested regions. Thirthahalli taluk from Shivamogga district of Karnataka has been reporting a consistently high burden of KFD. We describe the epidemiology of KFD cases in Thirthahalli taluk, identify high-risk groups, describe tick species and correlate KFD hot-spots with the number of cases.

Methods

We conducted a retrospective analysis of KFD surveillance data obtained from district surveillance unit, Shivamogga, on human, tick and monkey data, of Thirthahalli taluk from November 2017 to May 2022, described epidemiology, calculated the annual and seasonal time-trend of cases. We described the PHC-wise disease burden. We correlated number of cases with number of tick pools and/ or monkey carcass positive for KFDV and reported Pearson’s correlation coefficient.

Results

Thirthahalli taluk reported 326 cases, all were lab-confirmed using either RT-PCR (93%) or IgM-ELISA (7%); with an annual incidence rate of 45.9 per 100,000 population, 58% in males and median age 40 (IQR 28–51) years. The case fatality rate was 1.8%. Age groups with the highest average annual incidence were 45 to 49 years (8.4 per 100,000 population) and 50–54 years (8.1 per 100,000 population). Most (72%) cases occurred from February to April, and in the years 2019 (38%) and 2020 (44%) crossing the outbreak threshold. Among 16 Primary Health Centres (PHCs) under Thirthahalli, the population coming under six PHC reported 84% of cases and all deaths. Among 696 tick pools collected from 2018 to 2022, 31 were positive for KFDV (tick pool positivity 4.5%) and three monkey carcasses were KFDV positive. All identified KFDV-positive ticks belonged to the nymphal stage of the genus Haemaphysalis, and species included H.spinigera (23%), H. leachi (10%), and H. turturis (7%). There was correlation between number of human cases in a PHC and tick pool positivity (r = 0.62); and positive tick pools and positive monkey carcasses (r = 0.71).

Conclusion

Thirthahalli taluk had an ongoing endemic transmission of KFD during the study period including two outbreaks in consecutive years. Age groups most at risk for the disease were middle-aged adults. All deaths occurred in PHCs with a high case burden. All KFDV-positive ticks belonged to the nymphal stage of the Haemaphysalis genus. Occurrence of human cases per year was moderately correlated with tick pool positivity. We recommend continued tick surveillance and monkey carcass testing to map disease hot-spots; and targeted interventions in high-burden PHCs and at-risk age groups for effective disease control.