Melioidosis and glanders
Melioidosis and glanders are infectious diseases with similar clinical presentations, caused by species of the bacterial genus Burkholderia. Both have the potential to produce fatal disease and are considered potential biological warfare agents because they are highly infectious, especially by inhalation. In nature, the two diseases differ in their geographical spread, ecology, and route of transmission.
Melioidosis is an uncommon tropical disease caused by the bacterium, Burkholderia (formerly Pseudomonas) pseudomallei. Melioidosis is endemic in Southeast Asia and northern Australia, and cases also occur in the South Pacific, Africa, India, the Middle East, Central America, and South America.
Melioidosis predominantly occurs in people who have frequent contact with soil or surface water, such as workers in rice paddies, particularly during the rainy season. B pseudomallei are spread to humans and animals via contact with contaminated soil (especially through skin abrasions), inhalation of dust and ingestion of contaminated water. Person-to-person transmission is rare.
In healthy people, infection with B pseudomallei may cause no symptoms. In people with chronic diseases, such as diabetes mellitus, the illness may be severe, and even fatal. The incubation period can range from 1 day to 2 months. Four patterns of illness have been recognised.
1. Acute, localised infection
Acute, localised infection has a rapid onset and short course and results from inoculation through a skin abrasion. A nodule (small bump) develops at the site of entry which may ulcerate and can be associated with fever and muscle aches; this may progress rapidly to a bloodstream infection (septicaemia).
2. Pulmonary infection
Lung infection can range from mild bronchitis to severe pneumonia. Chest pain and cough develop along with a fever, headache, loss of appetite, and muscle aches. Skin abscesses may develop and take months to appear.
Septicaemia or acute bloodstream infection is the most severe form of melioidosis. It mainly occurs in people with underlying conditions such as HIV, kidney disease, and diabetes. The symptoms vary depending on the site of original infection but generally include breathing difficulties, headache, fever, diarrhoea, pus-filled lesions on the skin, abscesses throughout the body, muscle tenderness, and confusion.
4. Chronic suppurative infection
Multiple abscesses arise throughout the body, including the skin, muscles, and internal organs.
Melioidosis can also reappear clinically at times of stress many years after the primary infection, as has been reported in American veterans of the Vietnam War.
- Microscopy with Gram stain and culture may reveal B pseudomallei in the blood, urine, sputum, or skin lesions.
- Antibodies to B pseudomallei may also be detected in blood samples.
- Antibiotics such as ceftazidime or amoxicillin and clavulanate, with or without cotrimoxazole. Antibiotics must be given for about 20 weeks to avoid relapses.
- Admission to an intensive care unit is required for supportive therapy.
- Abscesses may need to be surgically drained.
Glanders is a rare sporadic disease caused by the bacterium Burkholderia (formerly Pseudomonas) mallei. Glanders is primarily a disease of horses and other animals and is commonly seen in domestic animals in Africa, Asia, the Middle East, and Central and South America. Infection with B mallei occurs in people in direct contact with infected animals. The bacteria enter the body through an abrasion of the skin or through mucosal surfaces of the eyes, nose, and respiratory tract. Cases of person-to-person transmission have been reported.
Glanders may follow an acute or chronic relapsing course. After an incubation period of 1 day to 2 weeks, patients with acute glanders develop generalised symptoms such as fever, muscle aches, chest pain, and headache. Additional symptoms depend on the route of infection and follow a similar pattern to melioidosis.
1. Localised skin infection
If there is an area of broken skin, a localised infection can occur at the site of inoculation. This presents as a cellulitis, which breaks down into an irregular ulcer. Lmphangitis (a red streak tracking to nearby lymph nodes) develops and swollen lymph nodes or abcesses may also occur.
If bacteria enter via the mucous membranes of the eyes, nose, or respiratory tract, excess mucous production occurs. It can destroy the nasal septum and palate. The lymph nodes in the neck become enlarged, giving rise to the name glanders (from French glandre). The infection may then become systemic.
2. Pulmonary infection
Pneumonia, lung abscesses, and pleural effusion (excess fluid surrounding the lungs) may develop.
3. Bloodstream infection (septicaemia)
Skin papules (small bumps), pustules (small bumps containing pus), bullae (big blisters), ulcers and abscesses may be present, and multiple organ systems are affected. Glanders bloodstream infections are usually fatal within 7 to 10 days.
4. Chronic infection
Multiple abscesses develop in the liver, spleen, skin, or muscles. This form is also known as ‘farcy’.
- Microscopy with Gram stain and culture may reveal B mallei in the blood, urine, sputum, or skin lesions.
- Serologic assays are not available to detect antibodies to B mallei.
The treatment of glanders is with sulfadiazine. B mallei is usually sensitive to tetracyclines, ciprofloxacin, streptomycin, novobiocin, gentamicin, imipenem, ceftazidime, and the sulphonamides.