Mycobacterium microti infection associated with spindle cell pseudotumour and hypercalcaemia: a possible link with an infected alpaca

Abstract

A 44-year-old woman who had recently been on immunosuppressive therapy presented with malaise, cough, fever, weight loss, lymphadenopathy, severe hypercalcaemia and a paratracheal mass on imaging. The initial impression was of disseminated malignancy, and lymphoma was suspected. A mediastinal biopsy showed a mycobacterial spindle cell pseudotumour containing acid and alcohol fast bacilli (AAFB). Sputum microscopy demonstrated AAFBs, confirmed as Mycobacterium tuberculosis complex by PCR. Prolonged culture grew Mycobacterium microti, an organism often associated with disease in small rodents and llamas. M microti isolates from postmortem samples of an alpaca at a nearby farm were genetically indistinguishable. Although the patient had not visited the farm, concurrent illness in her adopted stray cat suggested a possible zoonotic connection. The patient responded to antituberculous therapy, and rehydration and pamidronate for hypercalcaemia. We believe the hypercalcaemia was caused by a similar mechanism to raised calcium levels sometimes seen in tuberculosis.

Feline cutaneous mycobacteriosis: a review of clinical, pathological and molecular characterization of one case of Mycobacterium microti skin infection and nine cases of feline leprosy syndrome from France and New Caledonia

“…Mycobacterium microti infection in humans is described in immunocompromised as well as immunocompetent patients . Circumstantial evidence suggests a possible zoonotic connection with cats, but this has never been proved . In our case, the cat owner remained healthy.…”

Zoonotic diseases in South American camelids in England and Wales

“…However, a causal association between the alpaca and patient was not confirmed and other possible sources of infection were noted. [13] Cryptosporidiosis Cryptosporidiosis is a common enteric infection of humans and animals. Human infection with Cryptosporidium spp.…”

“…[12] Mycobacterium microti infection is even more uncommon in humans and only 25 human cases have been reported worldwide in the published literature. [13][14][15] In SAC, clinical signs of TB may include weight loss, inappetence, exercise intolerance and an intermittent cough. In some animals there is a short period of illness terminating with respiratory signs.…”

“…Human cases of confirmed M. bovis infection usually represent <1% of all culture-positive human TB cases in England and Wales [12]. M. microti infection is even more uncommon in humans and only 25 human cases have been reported worldwide in the published literature [13–15].…”

“…Only one of the cases (a 44-year -old woman from Scotland) was known to have had a possible connection to SACs. However, a causal association between the alpaca and patient was not confirmed and other possible sources of infection were noted [13].…”