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

160 BACTERIOSESCattle of all ages are susceptible. The course of the disease is more severe incalves, which experience stunted growth and variable mortality rates.Quick-spreading epizootics are characterized by a high morbidity rate. It is possiblethat rapid passage of the leptospires from one animal to another intensifiestheir virulence. In slow-moving epizootics, the rate of inapparent infection variesfrom one herd to another.Treatment with high doses of penicillin G or tetracycline is recommended foracute leptospirosis. Dihydrostreptomycin (12.5 mg/kg of bodyweight twice a day)may also be used, but due to its potential toxicity, treatment should be suspendedafter three days. Another suggested treatment is intramuscular sodium ampicillin (20mg/kg of bodyweight twice a day). In the chronic disease caused by pomona, it hasbeen repeatedly shown that a single intramuscular injection of dihydrostreptomycin(25 mg/kg of bodyweight) eliminates the infection from the kidneys of most animalstreated. However, this treatment fails in the case of infection caused by hardjo,although the number of leptospires is apparently reduced (Ellis et al., 1985).SWINE: The serovars most often isolated from swine in the Americas and in therest of the world are pomona, tarassovi, grippotyphosa, canicola, and icterohaemorrhagiae,as well as bratislava and muenchen of the Australis serogroup.Swine are a very important reservoir of pomona, with abundant and prolongedleptospiruria. The clinical infection varies from one herd to another. In some cases,infection occurs subclinically, although the animals may exhibit a fever lasting a fewdays; in others, the infection produces such symptoms as abortion and birth of weakpiglets. Stunted growth of piglets, jaundice, hemoglobinuria, convulsions, and gastrointestinaldisorders have also been seen. At times, meningitis and nervous symptomatologyare present. Abortion usually occurs between 15 and 30 days after infection.The principal serovars that cause abortions or stillborn piglets are pomona,tarassovi, and canicola. Infection that occurs during the last third of pregnancy isthe most critical in interrupting gestation. Leptospires of the serovars bratislava andmuenchen localize in the kidneys and in the genital tract of swine, as do hardjo leptospiresin cattle.As in cattle, a single intramuscular injection of dihydrostreptomycin (25 mg/kg ofbodyweight) is recommended for chronic infections caused by pomona.HORSES: Horses react serologically to many serotypes prevalent in the environment.Pomona has been isolated from these animals in the United States, and hardjohas been isolated in Argentina. In Europe, icterohaemorrhagiae, sejroe, and canicolahave been isolated, as well as pomona. Most infections are inapparent. Theremay be photophobia, watery eyes, edema of the ocular conjunctiva, miosis, and iritisin the acute phase of the disease. In the chronic phase, there may be anterior andposterior adhesions, a turbid vitreous body, formation of cataracts, uveitis, and otherophthalmologic abnormalities (Sillerud et al., 1987). Abortions may occasionallyoccur in infected mares (Bernard et al., 1993).Corneal opacity, which is frequently a sequela of the acute phase, can be reproducedthrough inoculation of inactivated leptospires from various serovars. An antigenrelationship has also been demonstrated between L. interrogans, crystallin, andthe cornea (Parma et al., 1986). Often, the disease’s sequela (periodic ophthalmia)is recognized instead of the acute, febrile phase. The onset of periodic ophthalmiaoccurs when the febrile phase has disappeared, after a latent phase that sometimes