Thomas and Fletcher also pioneered the use of serological methods in diagnosing the disease. Thomas and Fletcher incorrectly believed that melioidosis infection came from human contact with rodents. However, observations on the disease noted that humans usually got it after exposure to mud or contaminated water. Besides, the organism was never grown from rats. This led to a search of the bacteria in the environment. In 1936, the first animal (pig) case of melioidosis in Africa was reported in Madagascar. In 1937, water was first identified as the habitat of B. pseudomallei. The first case of Australian melioidosis was described in an outbreak in sheep in 1949 at North Queensland. This was followed by the first case of human melioidosis at Townsville in 1950. Initially, the discovery of melioidosis in Australia had led to a debate on when and how the disease spread from Southeast Asia to a new distant environment. However, this hypothesis was later disproved in 2017 when whole genome sequencing of B. pseudomallei over 30 countries collected over 79 years suggested Australia as the early reservoir for melioidosis. In 1955, first case of local human melioidosis was reported in Thailand. During the Vietnam War from 1967 to 1973, 343 American soldiers were reported with melioidosis, with about 50 cases transmitted through inhalation. An outbreak of melioidosis at the Paris Zoo in the 1970s (known as Laffaire du jardin des plantes) was thought to have originated from an imported panda or horses from Iran.
Serological tests
Serological tests such as indirect haemagglutination assay (IHA) have been used to detect the presence of antibodies against B. pseudomallei. However, different groups of people have widely different levels of antibodies, so interpretation of these tests depends on location. In Australia, less than 5% of people have B. pseudomallei antibodies, so the presence of even relatively low amounts of antibody is unusual and could suggest melioidosis. In Thailand, many people have antibodies against B. pseudomallei so the diagnosis of melioidosis should not be reliant entirely on the serological tests done in endemic areas. Indirect immunofluorescent test (IFAT) uses either B. pseudomallei or B. thailandensis antigens to look for the total number of antibodies in human serum. Using IFAT is labour intensive and is not used in large scale investigations.Antigen detect tests allow rapid detection of melioidosis. Examples of antigen detection tests are: latex agglutination test and ELISA. Latex agglutination uses antibodies coated on latex beads to detect B. pseudomallei antigens in solid or liquid media, although not all the assays can detect different species of Burkholderia. Latex agglutination is useful in screening for suspected B. pseudomallei colonies. IgG and IgM ELISAs has been used to detect lipopolysaccharide (LPS) antigens of B. pseudomallei, but plagued with low sensitivity. Commercial ELISA kits for melioidosis no longer available in the market due to low sensitivity to human antibodies detection. Nevertheless, antigen detection tests may be useful in severely ill patients because the bacterial load is high enough for detection.