The clinical manifestation of the disease can range from simple skin changes such as abscesses or ulcerations to severe organ problems. The commonest organs affected are liver, spleen, lungs, prostate, and kidneys. Among the most common features are bacteremia (in 40 to 60% of cases), pneumonia (50%), and septic shock (20%). People with only pneumonia may have a prominent cough with sputum and shortness of breath. However, those with septic shock together with pneumonia may have minimal coughing. Results of a chest X-ray can range from diffuse nodular infiltrates in those with septic shock to progressive consolidation located most commonly in the upper lobes for those with pneumonia only. Pleural effusion and empyema are more common for melioidosis affecting lower lobes of the lungs. In 10% of cases, people develop secondary pneumonia caused by other bacteria after the primary infection. In northern Australia, 60% of the infected children presented with only skin lesions, while 20% presented with pneumonia.Depending on the course of infection, other severe manifestations develop. Approximately 1 to 5% of those infected develop inflammation of the brain and brain covering or brain abscess; 14 to 28% develop pyelonephritis, kidney abscess or prostatic abscesses; 0 to 30% develop neck or salivary gland abscesses; 10 to 33% develop liver, spleen, or paraintestinal abscesses; and 4 to 14% develop septic arthritis and osteomyelitis. Rare manifestations include lymph node disease resembling tuberculosis, mediastinal masses, pericardial effusion, mycotic aneurysm, and inflammation of the pancreas.
It is unclear how imported melioidosis is able to persist in a completely new environment. Eventually, the outbreak terminated by itself after a period of time. It was only during the 1980s, Infectious Disease Association of Thailand started took notice of this disease. First conference on melioidosis was held in 1985 in Thailand. It was during this meeting that collaboration between Sappasitprasong Hospital, Thailand, and Wellcome-Mahido-Oxford Tropical Medicine Research Programme was established. Such collaboration made Thailand a world leader in clinical and epidemiology research on melioidosis.In 1989, several studies conducted in Thailand demonstrated ceftazidime as an effective antibiotic against melioidosis. Ceftazidime had been shown to reduce the risk of death of melioidosis from 74% to 37%. In 1990, a non-virulent arabinose-positive B. pseudomallei was found by Vanaporn Wuthiekanun. The organism was later reclassified into a new species called B. thailandensis. This species has become a useful tool in the laboratory for the studies of the pathogenesis of B. pseudomallei. B. pseudomallei was previously classified as part of the genus Pseudomonas. In 1992, the pathogen was formally named B. pseudomallei. In 1994, First International Symposium on melioidosis was held in Kuala Lumpur where 80 delegates attended. Papers were presented and later published as a book. Subsequent congresses were held in Thailand, Australia, and Singapore once every three years. In 2002, B. pseudomallei was classified as a "Category B agent". In 2004, the complete genome of B. pseudomallei was published.