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

LEPROSY 153were first observed, the animal began to suffer deformities and paralysis of theextremities. Histopathologic findings indicated the subpolar or intermediate lepromatousform, according to the Ridley and Jopling classification. The disease wasprogressive, with neuropathic deformation of the feet and hands. It seemed toregress when specific treatment was administered. The animal apparently acquiredthe disease from a patient with active leprosy. Experimental infections carried out todate have indicated that these animals may experience a spectrum of different formssimilar to those seen in man (Meyers et al., 1985).Source of Infection and Mode of Transmission: Man is the principal reservoirof M. leprae. The method of transmission is still not well known due to the extendedincubation period. Nevertheless, the principal source of infection is believed to belepromatous patients, in whom the infection is multibacillary, skin lesions are oftenulcerous, and a great number of bacilli are shed through the nose; similarly, bacilliare found in the mouth and pharynx. Consequently, transmission might be broughtabout by contact with infected skin, especially if there are abrasions or wounds.Currently, particular importance is attributed to aerosol transmission. Nasal secretionsfrom lepromatous patients contain approximately 100 million bacilli per milliliter.In addition, M. leprae can survive for about seven days in dried secretions.Another possible route of transmission is mother’s milk, which contains a largenumber of bacilli in lepromatous patients (Bullock, 1990). Oral transmission andtransmission by hematophagous arthropods are not discounted, but they are assignedless epidemiological importance.Until recently, leprosy was believed to be an exclusively human disease. However,research in recent years has demonstrated that the infection and the disease alsooccur naturally in wild animals. Although some researchers (Kirchheimer, 1979)have expressed doubt that the animal infection is identical to the human, the accumulatedevidence indicates that the etiologic agent is the same. The criteria (Binfordet al., 1982) used to identify the bacillus in animals as M. leprae were as follows:(1) selective invasion of the peripheral nerves by bacilli, since the onlyMycobacterium known to date to invade the nerves is M. leprae, (2) failure to growon common laboratory media for mycobacteria, (3) positive pyridine test to eliminateacid-fastness, (4) positive dopa test, (5) characteristic multiplication in mousefoot pads and in armadillos, and (6) reactivity of lepromin prepared with animalbacilli compared to that of standard lepromin.The origin of the infection in animals is unknown. Some authors believe thatarmadillos contracted the infection from a human source, perhaps from multibacillarypatients before the era of sulfones. In this regard, it should be pointed out thatleprosy bacilli may remain viable for a week in dried nasal secretions and thatarmadillos are in close contact with the soil. The high prevalence in some localitieswould also indicate that armadillos can transmit the disease to each other, either byinhalation or direct contact. Another possible transmission vehicle is maternal milk,in which the agent has been detected (Walsh et al., 1981). It has also been suggestedthat transmission among armadillos may be brought about by thorns penetrating theears, nose, or other body parts (Job et al., 1986b), as apparently armadillos useplaces with spiny plants to hide from their predators. These authors have foundthorns in the ears of 25.5% of 494 armadillos captured in Louisiana, and in the noseof 36.6% of them.