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

340 MYCOSESamong workers in a lime quarry in northern Michigan, an area not consideredendemic (Waldman et al., 1983). Another outbreak occurred in 1978–1979 at theIndianapolis campus of Indiana University, affecting 435 people. Again in1980–1981, an outbreak in an area close to the same university affected 51 people(Schlech et al., 1983). Histoplasmosis is considered the most common systemicmycotic infection in the United States (Loyd et al., 1990). There are also endemicregions in Latin America. Although prevalence varies from region to region, it hasbeen claimed that the entire population of Latin America lives within or near areaswhere the infection can be contracted (Borelli, 1970). In Mexico, epidemic outbreaksor isolated cases of the disease have been recorded in all but two states. Therewas a study of 11 outbreaks affecting 75 people in 1979, with mortality at 5.3%, and12 outbreaks affecting 68 people in 1980. Most of the cases occurred in people whofor occupational, educational, or recreational reasons had visited caves, abandonedmines, and tunnels in which bat droppings had accumulated. More than 2,000 largemines have had to be abandoned because of the presence of H. capsulatum due tolarge bat colonies (OPS, 1981). There are also endemic areas in Guatemala, Peru,and Venezuela (Ajello and Kaplan, 1980). In Cuba, three outbreaks, one of whichaffected 521 people, occurred between 1962 and 1963. In 1978 there was an outbreakamong students who visited a cave in the province of Havana; more recently,in a cave in the city of Morón, seven of eight spelunkers contracted the disease(González Menocal et al., 1990).Although the infection is common, the clinical disease is much less so.Radiography revealed pulmonary calcifications in a high percentage (about 25%) ofpeople reacting to histoplasmin. Approximately 90% of those who have a positivereaction to the histoplasmin hypersensitivity skin test are clinically normal.In Africa, there are some 200 known cases of histoplasmosis due to the duboisiivariety (Coulanges, 1989).Occurrence in Animals: Many species of domestic and wild mammals are susceptibleto the infection. Surveys using the histoplasmin test have shown that infectionis frequent in cattle, sheep, and horses in endemic areas. Dogs are the animalspecies in which the infection appears most frequently with clinical symptoms. Of14,000 dogs admitted to the University of Ohio clinic (USA) over the course of fouryears, histoplasmosis was diagnosed in 62 (0.44%) (Cole et al., 1953).The Disease in Man: When conidia are inhaled, they can lodge in the bronchiolesand alveoli. After a few days, they germinate and produce yeasts that are phagocytizedby macrophages where they proliferate. The macrophages move toward themediastinal lymph nodes and the spleen. When immunity develops, themacrophages acquire the ability to destroy the phagocytized yeasts, and the infiltratesin the nodes and other infection sites disappear (Loyd et al., 1990). Mostinfections occur asymptomatically. The development of the disease depends on thenumber of conidia inhaled and on the individual’s cellular immunity. The incubationperiod lasts from 5 to 18 days. There are essentially three clinical forms of the disease:acute pulmonary, chronic cavitary pulmonary, and disseminated. The acutepulmonary form is the most frequent and resembles influenza with febrile symptomsthat may last from one day to several weeks. A high percentage of patients alsoexperience cough and chest pain. In most patients, chest radiographs show nochanges, but in other cases small infiltrates and an increase in the hilar and