What is melioidosis, and should Hongkongers be worried about disease that has killed at least 11 monkeys?
Hong Kong Free Press
The deaths of at least 11 monkeys in a zoo in central Hong Kong as a result of melioidosis has thrust the bacterial infection into the spotlight. But it is not new to the city.
An outbreak in Sham Shui Po in 2022 claimed the lives of nine residents, though their deaths garnered less media attention than the deaths of the monkeys in the Hong Kong Zoological and Botanical Gardens, which now number 12.
HKFP examines what causes the disease.
What causes melioidosis?
Melioidosis is an infectious disease caused by the bacterium Burkholderia pseudomallei, which is commonly found in soil and water – particularly in moist clay soil – in tropical and subtropical regions. The disease is endemic to Hong Kong, and several cases of infection are reported by the Centre for Health Protection (CHP) each year. It can affect both humans and animals.
Infections arise through contact with contaminated soil and water, especially through skin abrasions or open wounds; by inhaling contaminated dust or water droplets; and by ingesting contaminated water.
People with underlying health conditions or compromised immune systems are at greater risk of contracting melioidosis.
Extreme weather, such as typhoons, can increase the likelihood of infection.
Issuing an appeal for “heightened vigilance” against the disease after Super Typhoon Saloa and record rainfall last September, the CHP said: “According to overseas literature and local data, Burkholderia pseudomallei in the soil and muddy water may be exposed to the ground after typhoons or storms, and the bacteria would spread more easily with strong wind and storms.”
How many melioidosis cases are there in Hong Hong each year?
Hong Kong reported its first human case of melioidosis in 1983, according to the CHP, while Hospital Authority records show that the annual number of confirmed cases from 2017 to 2021 ranged between three and 17.
However, it was not until November 2022 that melioidosis became a statutory notifiable disease, meaning that notification of any suspected or confirmed cases is required by law.
That year saw a surge in cases, with 46 infections confirmed in total. Of them, 37 were recorded between August and December, 30 of which involved residents of Sham Shui Po – one of the city’s poorest districts.
The median age of those infected, who lived within a kilometre of each other, was 71, while all suffered from chronic diseases and 18 had Type 2 diabetes. Nine died.
Water samples collected from their homes and the reservoirs servicing the district tested negative for Burkholderia pseudomallei. But some environmental samples collected from the home of one of those infected, as well as soil from a nearby construction site and soil from the rooftop or surface swabs of reservoirs’ air vents, returned positive results.
Although it was determined that the water supply system was not contaminated, the Water Supplies Department increased residual chlorine levels and installed filters at the air vents of the reservoirs.
In a document published in February, the CHP hailed these measures and “increased awareness among the public” for a “notable drop in cases.”
Last year, 17 melioidosis infections were reported, while there have been 19 recorded in 2024, to date.
Responding to enquiries from HKFP, a Department of Health spokesperson said the 82 cases of melioidosis recorded in 2022, 2023 and so far this year were aged between 42 and 94, with a median age of 70. They resided in 13 different districts: Eastern, Islands, Kwai Tsing, Kwun Tong, Sai Kung, Sha Tin, Sham Shui Po, Southern, Tai Po, Tuen Mun, Wan Chai, Wong Tai Sin and Yau Tsim Mong.
“According to the attending physicians, 16 of them died of melioidosis. All fatal cases had underlying diseases or immunodeficiency,” the spokesperson said by email on Friday.
What are the symptoms of melioidosis?
Symptoms of melioidosis are many and varied, and their intensity differs. Patients can present with a localised infection, pneumonia, meningoencephalitis, or sepsis. Common symptoms include fever, headache, localised pain or swelling, ulcers, chest pain, coughing or coughing up blood, and swelling of regional lymph nodes, though these often depend on the site of the infection.
The incubation period can also vary, from a day to a few years, though according to the CHP it is usually two to four weeks.
How is melioidosis treated?
Melioidosis can be treated with antibiotics, and some chronic cases may need long-term treatment.
Can melioidosis be transmitted from person to person, or animal to person?
Person-to-person transmission is “rare but has been reported,” according to the CHP, adding that it could “occur through contact with the blood or body fluids of an infected person.”
As for animal-to-human transmission, the Government of the Northern Territory of Australia describes melioidosis as a zoonosis – a disease that can jump from a non-human to a human.
The Centre for Food Safety and Public Health at Iowa State University, in the US, says Burkholderia pseudomallei “is usually acquired from environmental sources, but a few zoonotic cases have been described.” These were often after skin lesions were exposed to infected animals, tissues including meat, or milk.
Those cases are extremely rare, and coming into contact with contaminated soil or water remains the most common form of transmission.
Why have so many monkeys got melioidosis?
Twelve monkeys kept at the Hong Kong Zoological and Botanical Gardens, a tourist attraction in a city-centre park, have died amid the melioidosis outbreak there, with 11 of their deaths thus far confirmed as a result of “sepsis induced by bacterium Burkholderia pseudomallei.”
A necropsy was underway on the latest dead monkey, with the Leisure and Cultural Services Department (LCSD), which manages the zoological garden, on Tuesday saying: “Similar lesions were also found in the tissues of relevant organs of the 12th monkey that died today.”
Biological anthropologist Michael Rivera from the University of Hong Kong told HKFP by email last Friday that melioidosis infections in primates were not uncommon in the region. But, he said, “both infections and deaths are more common among captive primates.”
“This is because captive primates may have weakened immune response due to the stresses of confinement, less of their natural social stimulus, and the lack of a natural environment,” Rivera said. The close proximity of zoo animals can also ease the spread of disease, he said.
Because of the disease’s potentially lengthy incubation period, Rivera said it was “reasonable to hypothesize there was a latent carrier and the infection spread across the primate population, causing severe outcomes like septicaemia and death for many of the previously uninfected.”
During a press conference to announce the findings of the necropsies of the first nine monkeys, Secretary for Culture, Sports and Tourism Kevin Yeung last Friday said experts suspected the melioidosis infection was due to digging work in the garden in early October.
Staff caring for the monkeys may have accidentally transferred contaminated soil to the primates’ cages on their shoes, he said, adding that the disease could also have been transmitted among the monkeys.
The mammals section of the Hong Kong Zoological and Botanical Gardens remained closed “to closely monitor the health conditions of the animals,” the LCSD said on Tuesday.
It added that the remaining 78 mammals, and the staff who cared for them, were displaying “normal” health conditions, saying: “The LCSD will also continue to provide protective gear and health monitoring for staff who take care of animals.”
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