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

158 BACTERIOSESthrough filters that block other bacteria. Two species are recognized: Leptospirainterrogans and L. biflexa. L. interrogans is pathogenic for man and animals; L.biflexa, a free-living saprophyte found in surface waters, is seldom associated withinfection in mammals.The species of interest as a zoonotic agent is L. interrogans. It has more than 200serologic variants, or serovars, which constitutes the basic taxon. Serovars aregrouped for convenience into 23 serogroups (which is not a recognized taxon) on thebasis of the predominant agglutinogenic components they share (Faine, 1982;Alexander, 1991). Through the use of ribosomal RNA gene restriction patterns, anattempt is being made to characterize L. interrogans serovars in order to establishthe bases for molecular typing (Perolat et al., 1990).Geographic Distribution: Worldwide. There are universal serovars, such as L.interrogans serovar icterohaemorrhagiae and serovar canicola, and serovars thatoccur only in certain regions. Each region has characteristic serotypes, determinedby its ecology. Leptospirosis has a high prevalence in tropical countries with heavyrainfall and neutral or alkaline soils.Occurrence in Man: Incidence varies in different parts of the world. The diseasemay occur sporadically or in epidemic outbreaks. In general, outbreaks are causedby exposure to water contaminated by the urine of infected animals. Several occupationalgroups are particularly at risk, such as workers in rice fields, sugarcaneplantations, mines, sewer systems, and slaughterhouses, as well as animal caretakers,veterinarians, and members of the military.Occurrence in Animals: The infection is common in rodents and other wild anddomestic mammals. Worldwide, the infection occurs in approximately 160 mammalianspecies (Alexander, 1991). Each serovar has its preferred animal host orhosts, but each animal species may be host to one or more serovars. Thus, for example,the serovar pomona has pigs and cattle as its principal hosts, but it may transitorilyinfect other host animals. Dogs are the principal reservoir of canicola, but itmay occasionally be found in foxes, swine, and cattle.The Disease in Man: Man is susceptible to a large number of serovars. The incubationperiod lasts from one to two weeks, although cases with an incubation periodof only two days or more than three weeks are known. The disease is characterizedby two phases, the bacteremic phase, lasting 7 to 10 days, and the leptospiruricphase, lasting from a week to several months. Clinical manifestations vary and havediffering degrees of severity. In addition, numerous cases of infection occur inapparentlyor subclinically. In general, two clinical types are distinguished: icteric andanicteric. The serious icteric, or hepatonephritic, type (Weil’s disease) is much lessfrequent than the anicteric type. Some authors estimate that this form occurs inapproximately 10% of cases. It is often associated with infection caused by icterohaemorrhagiae,but this is not the only serovar that can produce it. On the otherhand, numerous infections caused by icterohaemorrhagiae occur in anicteric form.In the classical form of Weil’s disease, the onset of symptoms is sudden, with fever,headache, myalgias, conjunctivitis, nausea, vomiting, and diarrhea or constipation.Prostration may be severe. Petechiae on the skin, hemorrhages in the gastrointestinaltract, and proteinuria are common. Hepatomegaly and jaundice, renal insufficiencywith marked oliguria or anuria, azotemia, and electrolyte imbalance develop