Disease Outbreak News

Anthrax - Thailand

29 May 2025
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Situation at a glance

In early May 2025, the International Health Regulations National Focal Point (IHR NFP) for Thailand notified WHO of four cases of cutaneous anthrax. One of the affected individuals died as a result of disease complications, while the remaining three cases were hospitalized and received appropriate medical care. All reported cases had direct contact with cattle suspected to be infected with anthrax. A rapid field investigation and response was conducted by the national health authorities. All potentially exposed individuals were identified, and all high-risk contacts received post-exposure prophylaxis. On 28 May, an additional case was announced who was associated with the slaughtering of cattle. Disease control measures, including animal quarantine, and vaccination campaign targeting cattle withing five km radius, public awareness campaigns, and enhanced surveillance, were implemented in the affected area. Anthrax is a life-threatening zoonotic disease caused by the spore-forming bacterium Bacillus anthracis. Humans can get anthrax from infected animals or contaminated animal products. It generally does not spread between people. Currently, due to the robust public health measures implemented by Thailand, the risk of international disease spread through animal movement remains low.

Description of the situation

Between 1 May and 4 May 2025, the Thailand IHR NFP notified WHO of four confirmed cases of cutaneous anthrax, including one death. The age range of the confirmed cases is 36 years to 58 years, comprising of three males and one female. The cases were identified in Mukdahan Province, located near the border with Lao People's Democratic Republic, separated by the Mekong River. All cases are epidemiologically linked to slaughtering of cows. The first cow was slaughtered on 12 April 2025, during a merit-making event, and its meat was distributed among villagers. A second cow was slaughtered on 28 April 2025. Exposure to meat or contact during the slaughtering process of these animals is believed to be the source of infection for all confirmed cases. 

The first case, presented with a skin rash on his right hand, which progressed to a clearly visible lesion by 24 April. Initially hospitalized, he was transferred to a referral hospital on 27 April due to worsening clinical symptoms, including a darkening lesion on the hand, swollen right axillary lymph nodes, dizziness, and convulsions. He subsequently died on the same day as a result of disease complications. The other three cases presented with pustular and vesicular lesions and were hospitalized. As of 28 May 2025, the three cases have completed a 10-day course of levofloxacin and doxycycline and have been discharged from hospital. 

Blood and wound samples from the four cases were collected between 28 April and 1 May and were sent to the Department of Medical Sciences (DMSC) and Bamrasnaradura Institute for laboratory testing. B. anthracis was confirmed by RT-PCR in all four patients.

Screening of at-risk individuals was conducted across three villages, identifying two additional suspected cases who presented with diarrhea and fever. However, the samples tested negative for B. anthracis.  A total of 636 individuals were identified as at risk and monitored till 10 May 2025. Among them, 28 people were directly involved in the slaughter of cattle, while others consumed raw beef. Public health authorities initiated post-exposure prophylaxis for at-risk individuals by administering doxycycline for a duration of seven days.

On 28 May, the Ministry of Public Health announced the fifth confirmed case in Mukdahan province, associated with the slaughtering of cows. The clinical status of the most recent reported fifth case is unknown at the time of reporting.

This is the first reported anthrax-related death in Thailand since 1994. According to the Division of Epidemiology, the most recent anthrax cases prior to this event occurred in 2000 (15 cases and no deaths in Phichit and Phitsanulok provinces) and in 2017 (two cases and no deaths in Tak province linked to handling a goat carcass imported from Myanmar).  

Epidemiology

Anthrax is a zoonosis caused by the Gram-positive, spore-forming rod B. anthracis, which affects predominantly grazing herbivores, both livestock and wildlife.

Spores of B. anthracis are the infectious forms and can remain viable in soil as well as animal tissues, parts, and products for years. They can also be dispersed by wind or floods, animal scavengers (feeding on infected carcasses), and transport of animal products.

In humans, anthrax spores can invade the body by four routes: transcutaneous inoculation, ingestion, inhalation, and direct injection. The disease clinical manifestations vary based upon the type of exposure: cutaneous, gastrointestinal, inhalation and injection-related anthrax, respectively. At the same time, all forms of anthrax can lead to disseminated disease, including sepsis and meningoencephalitis.

  • Cutaneous anthrax is the most common form and occurs in approximately 95% of cases. Infection follows direct contact with infected animals, carcasses, animal tissues, parts (e.g., hides, wool, hair, bone) or products (e.g., drums, brushes, rugs). Invasion through the skin may occur via skin abrasions or hair follicles. Additionally, cutaneous anthrax may occur as a result of contact with contaminated soil or skin lesions of an infected individual. However, direct person-to-person transmission is very rare. Individuals with cutaneous disease present with an itchy, painless papule (most commonly on exposed areas), which evolves into a larger vesicle or blister and eventually progresses into a necrotic ulcer with a black, depressed central crust (eschar). Local oedema (swelling) and regional lymphadenopathy are usually prominent. Fever, headache and malaise may occur in a minority of cases.
  • Gastrointestinal anthrax follows ingestion of contaminated, undercooked meat and is characterized by the presence of nausea, vomiting, abdominal pain, sometimes associated with diarrhea. Gastrointestinal hemorrhage and ascites may occur in severe cases. Some individuals present with oropharyngeal involvement.
  • Inhalation anthrax is the most severe clinical presentation and results from inhalation of spore-containing dusts or aerosols. Noticeably, airborne person-to-person transmission does not occur. Affected patients initially present with a flu-like illness, followed by severe respiratory distress and shock. 
  • Injection anthrax has been associated with use of drugs by any route (transcutaneous and intravenous) and is associated with skin lesions and soft tissue involvement. 

The main risk factor for anthrax is occupational exposure. At-risk categories include workers involved in industrial processing of hides, wool, hair or bone products, veterinarians, agricultural and wildlife workers in areas with high incidence of anthrax in animals and laboratory personnel.

Anthrax is endemic in several countries across the South-East Asia region. In Thailand, however, human cases of anthrax are a very rare occurrence. This is the first human anthrax outbreak in 25 years to result in a fatality in the country. The most recent prior cases occurred in 2017 in Mae Sot district, Tak province, where two anthrax cases were reported, but no deaths. Anthrax was first reported in Thailand in 1947. Between 1992 and 2000, the incidence rate ranged from 0.02 to 0.17 per 100 000 population, with most cases occurring in provinces bordering the Lao People's Democratic Republic and Myanmar. 

Public health response

The Department of Disease Control, Ministry of Public Health and the Department of Livestock Development, Ministry of Agriculture and Cooperatives, have implemented measures to control potential disease spread as follows: 

 Actions implemented for human health 

  • Environmental cleaning and disinfection were carried out in 23 high-risk households, identified based on consumption of potentially contaminated meat. 
  • Establishment of a drug distribution center to improve accessibility and streamline the delivery of post-exposure prophylaxis. 
  • Enhanced risk screening across three affected villages. 
  • Exposed individuals were identified and provided with post-exposure prophylaxis. 
  • The Department of Medical Sciences (DMSC) in Thailand conducted genomic sequencing as a key component of their testing strategy to better understand the transmission dynamics. 
  • Risk communication and community engagement efforts were undertaken, including information dissemination to villagers and public awareness campaigns conducted through various media channels. 

Actions taken for animal health 

  • Farmers were informed to report any sick or dead animals to officials and strictly advised against slaughtering or consuming raw meat. 
  • A total of 123 cattle herds from 21 farmers, suspected of being potential source of human infections, were quarantined. The animals were treated with penicillin for seven days and monitored for at least 20 days. 
  • Grazing and access to water sources in areas identified as contamination risks were restricted for livestock. A vaccination campaign targeting cattle and buffalo within a five-kilometer radius, was conducted, reaching a total of 1222 animals. In Thailand, anthrax vaccinations for animals are administered in response to outbreak situations. 
  • Animal quarantine officers established checkpoints to control the movement of animals in and out of the five-kilometer risk zone. Coordination was strengthened with the administrative sectors, police, military, and security agencies to increase the intensity of inspection, patrol, and to prevent the smuggling of animals, meat, and animal products from neighboring countries. 
  • Samples were collected from knives and cutting boards used by the first case, as well as from soil at the slaughter site and beef from the slaughtered cows. All tested positive for B. anthracis.

WHO risk assessment

Between 1992 and 2000, the incidence rate in Thailand for anthrax in humans ranged from 0.02 to 0.17 per 100 000 population, with most cases reported in provinces bordering the Lao People's Democratic Republic and Myanmar. 

While sporadic human cases have been reported over the past 25 years, Thailand has not experienced a large-scale outbreak since 1995, when 102 cases were recorded. In the current outbreak, human cases have been reported in Don Tan district, Mukdahan province, which borders the Lao People's Democratic Republic.  However, Thailand has taken immediate response actions including the restriction of animal movement. As a result, the risk of international spread is low.  

The risk for human health is low given the rapid and extensive public and animal health measures implemented. Although over 600 individuals linked to the first four cases, were identified as potentially exposed, all exposed individuals completed their monitoring period. Public awareness campaigns are ongoing at the national level. 

Animal health measures have also been robust, including the quarantine and treatment of suspected cattle herds, livestock vaccination within a five-kilometer radius, movement control, and enhanced inspections. Additionally, neighboring countries, such as Malaysia and the Lao People's Democratic Republic, have heightened anthrax surveillance, particularly in the context of animal movement. 

Although WHO does not recommend any restrictions on travel or trade, the current situation may lead to the imposition of animal trade measures. Some neighboring countries have already introduced restrictions on the importation of animals and animal products from Thailand. Any decisions regarding international travel and trade should be based on a thorough risk assessment and should be proportionate to the actual public health risks involved.

WHO advice

Prevention of anthrax in humans is primarily dependent on controlling the disease in animals. In the event of a suspected outbreak in livestock, key control measures include quarantining affected herds or flocks, proper disposal of carcasses, safe collection of specimens, decontamination of carcass sites and contaminated materials, vaccination of unexposed animal, and treatment of symptomatic animals. The general public and at-risk individuals should promptly report sick or unexpected deaths in animals to veterinary authorities. 

In the community setting, individuals who handle potentially contaminated animal products should be educated about anthrax transmission and clinical manifestations, wound care and personal hygiene. In case of any illness or symptoms of disease, they should immediately seek medical advice.

Anthrax poses a significant occupational risk to individuals who work closely with animals or animal products, particularly in environments where the disease is endemic.  Prevention through education, proper protective measures, and surveillance is key to reducing occupational exposure to anthrax. To reduce the risk of anthrax infection in these high-risk occupations, the following protective measures are recommended: use of Personal Protective Equipment (PPE), workplace hygiene and proper ventilation in workspaces, especially in industries where aerosols may be generated.  

In health-care settings, patients with suspected or confirmed zoonotic anthrax exposure may be cared for using standard precautions for infection prevention and control except where there is draining discharge of pus/blood/fluid at the site of a cutaneous anthrax lesion. When a patient has a suspected or confirmed cutaneous anthrax lesion, use soap and water handwashing during WHO’s 5 moments for hand hygiene instead of using alcohol-based handrub as sanitizers and antiseptics which are ineffective against anthrax spores.

If a patient presents with discharge of blood/pus/fluid at the site of a cutaneous anthrax lesion, apply contact precautions for infection prevention and control, including placing the patient in a private room and the use of disposable PPE (examination gloves and fluid-resistant gown). Use disposable consumable products when performing manual cleaning of the room of patients on contact precautions, including placing cloths and gloves used during cleaning in a leak-proof bag and sending this bag for incineration as infectious waste. Used linens and contaminated clothing with pus/blood/fluid discharge from cutaneous anthrax lesions should be placed in a leak-proof bag and either a) sent for incineration as infectious waste or b) sent for autoclaving (ensuring the autoclave function is verified using a spore strip) prior to normal laundry/linen management. Dressings and bandages used on cutaneous anthrax lesions should be placed in a leak proof bag and sent for incineration as infectious waste after use. When a patient no longer has discharge of pus/blood/fluid at the site of a cutaneous anthrax lesion; perform a terminal clean of the patient’s room and continue care on standard precautions with risk assessment for appropriate PPE unless otherwise indicated.

The cornerstone of treatment is timely initiation of antibiotic therapy, at the first clinical suspicion. The choice of antimicrobial regimens depends on the clinical form, severity, and resource availability. Individuals with documented or suspected gastrointestinal exposure may be offered a 10-day course of oral antibiotic prophylaxis. Post-exposure prophylaxis should be initiated as soon as possible, ideally within 48 hours. Recommended antibiotics include doxycycline or ciprofloxacin. 

International travelers to countries where anthrax is endemic should be aware of regulations concerning the importation of prohibited animal products, trophies, and souvenirs.  

Further information

Citable reference:  World Health Organization (29 May 2025). Disease Outbreak News; Anthrax in Thailand. Available at: https://www.who.int/emergencies/disease-outbreak-news/item/2025-DON573