Balamuthia mandrillaris infection

Balamuthia mandrillaris (B. mandrillaris) is an amoeba first discovered in 1990 and associated with more than 100 cases of disease since. Infection with B. mandrillaris has been reported in South, Central, and North America, Asia, Australia, and Europe but remains a rare cause of amoebiasis.

B. mandrillaris lives in water and soil and can enter humans through the nasal mucosa, lungs, or breaks in the skin. As in cases of other free-living amoebae (e.g. Naegleria and Acanthamoeba), a history of swimming in freshwater lakes, ponds, and heated swimming pools seems to be common.

Weeks to years later (5 to 8 months on average) the infection spreads to the central nervous system causing amoebic encephalitis (inflammation of the brain). Features include:

• fever
• focal neurological deficits (e.g. double vision has been commonly reported)
• symptoms of meningeal irritation (e.g. neck stiffness, intolerance to bright light)
• symptoms of increased intracranial pressure – e.g. headache, nausea and vomiting, reduced level of consciousness

In 95% of patients, B. mandrillaris encephalitis is fatal.

How does it affect the skin?

The dermatological significance of B. mandrillaris is that a typical skin lesion appears before the infection spreads to the central nervous system. The classical skin lesion is an asymptomatic granulomatous plaque (a nodule made of inflammatory cells), usually located on the central face. They are often described as rubbery in consistency. Single or multiple lesions may be present,

The lesion may enlarge (to involve the entire face in some cases), and occasionally gives origin to smaller satellite lesions. Ulceration occurs at a late stage. Occasionally the lesion may occur on the extremities.

How is the diagnosis made?

As this condition is unusual, diagnosis is often delayed. Diagnosis is made by finding the amoeba in the skin or other tissue. Biopsy shows tuberculoid granulomatous infiltrate within dermis and subcutaneous tissues. Trophozoites and cysts are rarely seen.

The organism is difficult to culture in the laboratory within normal culture media. It can be grown in specific mammalian cell culture lines or by innoculation of mice if there is clinical suspicion of balamuthia infection. A polymerase chain reaction (PCR) test has been developed for research purposes but is not currently available in community laboratories.

Treatment

Early treatment with a range of oral antifungal, anthelmintic, and antiprotozoal drugs (often in combination) may improve survival.