Leptospirosis is primarily a disease of domestic or wildanimals but it can be passed to humans or sometimes causes severe kidney orliver disease. The causative agent is the spirochete Leptospira interrogans. Leptospira has a characteristic shape forexample an exceedingly fine spiral, only about 0.1 micro meter in diameter,wound so tightly that is barely discernible under a dark-field microscope.
Likeother spirochetes, L. interrogans stainspoorly and is difficult to see under a normal light microscope. It is anobligate aerobe that can be grown in a variety of artificial media supplementedwith rabbit serum. Animalsinfected with the spirochete shed the bacteria in their urine for extendedperiods. Humans become infected by contact with urine-contaminated water orsoil or sometimes with animal tissue. People whose occupations expose them toanimals or animal products are most at risk.
Usually the pathogen entersthrough minor abrasions in the skin or mucous membranes. When ingested, itenters through the mucosa of the upper digestive system. In the United States,dogs and rats are the most common sources. Domestic dogs have a sizable rate ofinfections even when immunized they may continue to shed leptospira. Pathogenicleptospires usually lives in the kidneys of their natural host. The genitaltracts of domestic animals act as sites of persistence.
Mostly the mammalianspecies are carriers. Human are considered dead end hosts. Leptospires areexcreted through urine into the environment, where they can survive for severalmonths depending on the favourable environment. Infection to the accidentalhosts occurs via direct contact with the carrier’s urine or indirectly througha urine contaminated environment. Leptospires also can be excreted in theproducts of abortion in domestic animal species. Pathogenic leptospires enterthrough skin abrasions and cut and through the mucous membranes of theeyes,nose which inhalation of contaminated aerosols and mouth by theconsumption of contaminated beverage and predator chain transmission andgenital tracts by domestic animals. Penetration through water weakened skin iscontroversial.
Unlike natural hosts, accidental hosts often develop disease. To datenearly 300 pathogenic Lepstospira serovarshave been identified and many more will follow. Generally each serovar isadapted to a certain mammalian hosts such as rodents, insectivores, dogs, pigsand cattle comprise the best known ones. Serovars can be adapted to severalhosts while one hosts might carry several distinct serovars. Furthermore,serovars continue to adapt to new hosts because the cycle is complex anddynamic. Vaccination pressures may also alter the distribution of the serovarsin a species. Distribution and infection patterns may change both by adaptationof serovars to other hosts and by the introduction of new host animals into anarea.
Also climatic and ecological changes will affect the distribution of Leptospira serovars and consequently theprevalence and clinical features of human cases while anthropogenic practicesand animal management systems are likely to determine exposure and infectionrisks. The lackof awareness of leptospirosis is mainly due to the wide variety of symptomsseen in infected persons, the often subclinical nature of the disease inanimals and technically demanding laboratory tests making the disease difficultto diagnose both in the clinic and the laboratory. The illness varies from mildto severe, potentially fatal depending on a number of known or unknown factors,among which the causal serovar and the host’s immune status might be important.In the worldwide, case fatality rates range from 3 to more then 50%. Clinicalmanifestations may comprise fever, severe headache, chills, diarrhoea, nauseaand vomiting, haemorrhages, joint pain, skin rash, cough, cardiac arrhythmia,psychosis or delirium. Early disease presents with non-specific symptoms offever, myalgia and headache having lacking of any diagnostic hallmarkssuggestive of leptospirosis.
Because of its protein manifestations,leptospirosis almost look alike other infectious diseases namely influenza,hepatitis, dengue, hantavirus infections or other viral haemorrhagic fevers,yellow fever, malaria, brucellosis, typhoid fever or other enteric diseases andpneumonia together with a range of abortifacient diseases in animals. Usuallyeasy symptom that can be detected are after an incubation period 1-2 week,headaches, muscular aches, chills and fever abruptly appear. Several dayslater, the acute symptoms disappear and the temperature returns to normal. Afew days later, a second episode of fever may occur. In a small number of casesthe kidneys and liver becomes seriously infected (Weil’s disease) kidneyfailure is the most common cause of death.
Recovery results in a solid immunitybut only to the particular serovar involved.