The Centre for Health Protection (CHP) reported a case of B virus infection (Macacine Herpesvirus 1, Herpes 8, herpesvirus B) in a 27-year-old male on April 3, 2024.

Case Details:

• An incident involving an injury to a park visitor by macaque monkeys occurred at Kam Shan Country Park in the end of February.
• On 21 March 2024, an individual was admitted to the hospital after experiencing symptoms of encephalitis. He was receiving treatment in the intensive care unit and his condition was critical. So far, no close contacts have reported any symptoms.
• This is a first B virus case in Hong kong although there were cases reported in some countries e.g. The United States, Canada, Japan and mainland China.
• On April 3, B virus was detected in the patient's cerebrospinal fluid during laboratory testing conducted by the authority.

Additional Context:

• Old World macaques identified as natural reservoir for B virus. Infected macaques reported in Southeast Asia, including India, China, Malaysia, the Indonesian archipelago, and the Philippines. Notably, a cluster of infected macaques detected in Silver Springs State Park, Florida, US. Vigilance urged in regions of macaque presence to mitigate risk of transmission.
• Disease primarily poses zoonotic threat to occupational cohorts including veterinarians, animal care personnel, and laboratory researchers. Transmission typically occurs via bites or scratches from infected macaques or through direct contact with the mucous membranes of the monkey's eyes, nose, or mouth. Enhanced precautionary measures recommended for at-risk populations to minimize exposure risk.
• Disease onset typically manifests within one month following exposure. Early symptoms include fever, headache, myalgia, and occasionally vesicular lesions near the exposure site, alongside lymphadenopathy. Immediate medical assessment is advised upon symptom onset to facilitate timely intervention and management.
• The patient's clinical presentation is consistent with encephalomyelitis, a severe inflammatory condition of the brain and spinal cord. B virus was identified in the cerebrospinal fluid (CSF) analysis, suggesting a viral etiology. This finding is concerning as B virus infections in humans are often fatal even with treatment.
• Antiviral agents are recommended for post-exposure prophylaxis in high-risk scenarios. Valacyclovir is the preferred choice, with acyclovir being considered as an alternative. Upon diagnosis, initial treatment should commence with intravenous administration of acyclovir or ganciclovir to optimize therapeutic outcomes.

Response Measures:

Response measures are underway as Hong Kong authorities investigate the situation. Public advisories caution against interacting with or providing food to wild monkeys. In the event of monkey-inflicted injuries, immediate medical attention is strongly advised, in line with guidance from the Centre for Health Protection.

Level of Concern: 

This event is low concern at the regional and global level given:

1. Historically, the region has witnessed few reported cases of B virus, with the most recent instance involving a mainland China veterinarian in 2021. Despite the virus being identified nearly a century ago, its prevalence remains low in endemic nations.
2. Although literature acknowledges instances of human-to-human transmission, the primary mode of B virus acquisition is through exposure to macaque monkeys. To date, there is no substantiated evidence of ongoing human-to-human transmission in this particular case.
3. The primary risk of infection persists for individuals in contact with macaque monkeys due to their occupation and those engaging in activities with wild macaques in endemic regions, notably Southeast Asia.
4. Currently, there have been no documented infections in individuals who have undergone post-exposure prophylaxis with antivirals within three days of exposure to B virus.

Sources:

1. 香港政府新聞公報. (2024, April 3). 衞生防護中心調查一宗人類感染B病毒個案. 新浪香港. https://portal.sina.com.hk/news-hongkong/gia-info-gov-hk/2024/04/03/798746/衞生防護中心調查一宗人類感染b病毒個案/ 
2. News, B. (2024, April 4). Monkey Attack Leads to First Human Case of B Virus in Hong Kong - BNN Bloomberg. BNN. https://www.bnnbloomberg.ca/monkey-attack-leads-to-first-human-case-of-b-virus-in-hong-kong-1.2055047
3. news.gov.hk. (2024, April 3). HK logs 1st human B virus case. Hong Kong's Information Services Department. https://www.news.gov.hk/eng/2024/04/20240403/20240403_222910_316.html 
4. The Government of Hong Kong (SAR). (2024, April 6). Hong Kong enters influenza season. Www.info.gov.hk. https://www.info.gov.hk/gia/general/202304/06/P2023040600528.htm 
5. BlueDot (Event Alert), issued 04 April 2024.