Zoonoses: A Case Presentation

Abstract

ISSUE: Certain bacteria can cause disease in animals as well as humans. In some cases the bacteria is transmitted from the animal to the human. A case of Rhodococcus equine brain abscess was identified in a 26 year old intravenous drug user with exposure to horses.Once thought to be exclusively an equine pathogen, Rhodococcus equine infection is occuring in humans with an increasing frequency. It has been found in immunocompromised individuals including those with AIDS, small cell lung carcinoma, lymphoma, or lung and bone marrow transplant recipients. Very little is known about the pathogenesis of the disease except for its mode of transmission which is almost always via the droplet/ respiratory route. PROJECT: A patient was admitted to the hospital with the diagnosis of sinus infection. Her presenting signs and symptoms were right sided weakness, headache, and facial droop. Her mental status progressively declined. Lab studies included a negative HIV test and a CD4 count of 813. A CT of the brain revealed a thalamic brain lesion. Since the differential diagnosis included an infectious process the patient was empirically started on Vancomycin, Ceftriaxone, Metronidazole, Bactrim, Amphotericin B, and Acyclovir. A brain biopsy was performed on hospital day 60. RESULTS: On hospital day 64 brain tissue grew Rhodococcus equine, a bacteria that causes disease in horses. Upon further questioning of the patient's family a possible link was found. The family stated that the patient was known to inject herself with needles previously used on horses. LESSONS LEARNED: Although many zoonotic diseases have been reported this is believed to be the first case of brain abscess caused by Rhodococcus equine. A zoonotic disease should be considered in the differential diagnosis of any patient that works closely with animals. A thorough history is important. The patient's exposure to horses and her intravenous drug use were known, however more intense questioning may have yielded critical information about her injection practices. Clinical correlation is important so as not to disregard a culture result as a contaminant. In this era of bioterrorism it is important to consult with the state and national authorities to determine if an unusual organism has been earmarked as a potential agent of bioterrorism. As of this time Rhodococcus equine is not. When a brain biopsy of unknown etiology is performed consideration should be given to handling the instruments using a protocol for suspected prion disease.