zoonoses and communicable diseases common to ... - PAHO/WHO

230 BACTERIOSESCases are more frequent due to the AIDS epidemic and at least 20 more cases werereported from 1983 to 1990 (Prescott, 1991). In many parts of the world, particularlyin developing countries, physicians and hospital microbiologists know littleabout this disease. Consequently, underreporting is possible.Occurrence in Animals: Infection due to R. equi is recognized worldwide as animportant cause of bronchopneumonia, ulcerative enteritis, and lymphadenitis infoals, and less frequently in other animal species (Barton and Hughes, 1980).The Disease in Man: As in other animals, in man the lungs are the organ mostoften affected. The disease appears with a fever lasting several days to severalweeks, discomfort, dyspnea, unproductive cough, and, frequently, chest pain.Initially, x-rays show infiltration with nodular lesions, particularly in the superiorlobes of the lungs. If the patient is not treated, the granulomatous lesion can developinto suppuration and cavitation. Extrapulmonary cases, such as osteomyelitis, hemorrhagicdiarrhea and cachexia, pleurisy, abscesses, and lymphadenitis occur rarely(Prescott, 1991).The infection and the disease appear in immunocompromised patients. R. equi isan intracellular parasite of the macrophages, which explains the pyogranulomatousnature of the disease and the predisposition of patients with cell-mediated immunesystem defects. Currently, AIDS patients represent 88% of cases. The remainingcases are patients undergoing immunosuppressive treatment due to neoplasias or anorgan transplant. HIV-infected patients have a higher incidence of simultaneoussecondary infections and higher mortality (54.5% as compared to 20% for patientsnot infected with HIV).Given the intracellular nature of rhodococcosis, the efficacy of the antimicrobialagent depends on its ability to penetrate the phagocytes. R. equi is sensitive to erythromycin,vancomycin, amikacin, gentamicin, neomycin, and rifampicin. Surgicalresection of the lesion or lesions is an important part of treatment (Prescott, 1991;Harvey and Sunstrum, 1991). The survival rate was 75% when antibiotic treatmentwas combined with surgical resection of the infected tissue. The survival rate forthose who received only antibiotics was 61% (Harvey and Sunstrum, 1991).The Disease in Animals: Rhodococcosis is a disease that occurs primarily in foalsfrom 2 to 6 months of age, and particularly from 2 to 4 months of age. This susceptibilityof young foals could be because at that age the passive immunity conferredby the mother is in decline and the animal’s own immune system is still immature.Foals older than 6 months are resistant, unless they have a defect in cellular immunityor another concurrent disease with a debilitating effect (Yager, 1987).Equine rhodococcosis appears as a subacute or chronic suppurative bronchopneumonia.Formation of abscesses is extensive, accompanied by a suppurativelymphadenitis. The lesions progress slowly. The degeneration of the macrophagescoincides with the lysis of pulmonary parenchyma. Formation of abscesses continueswith expansion of the purulent center. The infection is spread through the lymphaticsystem and affects the regional lymph nodes. Despite bacteremia no lesionsare found in the liver or spleen, which would indicate that fixed macrophages coulddestroy R. equi in the circulatory system. It is estimated that approximately 50% offoals with bronchopneumonia develop concomitant ulcerative colitis and typhlitis. Asmall number of foals develop only intestinal lesions (Yager, 1987).