Zoonoses disease-leptospirosis, Biology


Leptospirosis is a general term that denotes all infections of man and animals caused by spirochaetes of the genus Leptospira. At one time, the infection had been given several distinctive names such as Weil’s disease, flood fever, mud fever, trench fever, rice field fever, swamp fever, seven days fever of Japan, etc. Leptospirosis is a widespread zoonosis. In tropical countries like India, it is of much significance because the climate provides favourable conditions for the survival of the causative agents throughout the year. Animals may suffer from clinical disease or remain asymptomatic carriers excreting the organisms in the urine.

The pathogenic leptospires which belong to the species Leptospira interrogans are classified into a number of serogroup serotypes (serovars). About 18 serogroups and more than 170 serotypes are recognized from the different parts of the wo rld .    The  predominant    serotype s    are    and amana ,hardjo , Pomona,ieterohaemorrhagiae, lebdomandis, canicola, grippotyphosa, semoranga, etc. Cattle, sheep, goat, horse, pigs, dogs, cats, rats and many other rodents and wild animals including deer, foxes, squirrels, etc. act as carriers and excrete leptospires. Leptospires excreted in urine and faeces contaminate surface water, paddy fields and sugarcane fields. Placenta, aborted fetuses and uterine discharges are loaded with leptospires. Thus, leptospirosis is an important occupational disease for rice and sugarcane field workers, plantation workers, soldiers, veterinarians, slaughter house workers, poultry and fish handlers and swine herd packing house workers. The infection is acquired through direct contact with infected materials and animals or through ingestion of food contaminated with the urine of infected animals.

Clinical features:
Previously, it was widely believed that the different serotypes were associated with distinct clinical syndromes in man and animals, for examples, sero typ e  H a r d j o  c o mmo n ly  c a u se s  an  influe n z a  l ik e  i l ln e ss ,  s e r o t yp e Icterohaemorrhagiae causes jaundice and serotype Fortbragg causes fever and pretibial rash. It is now clear that there are no serotype specific syndrome in either man or animals and that the pathogenesis in all cases of leptospirosis is basically the same. Leptospirosis occurs in two forms, anicteric and icteric (Weil’s syndrome) – neither of which is constantly related to a particular serotype.

The incubation period is about 8 to 12 days. Onset is abrupt, often with chills followed by high fever. Headache, photophobia and sever muscular pain, particularly in the back and legs, are prominent symptoms. The most constant physical sign is conjunctivitis. The classic icterohaemorrhagic picture is rarely seen. Albuminuria is common but jaundice occurs in about 10 % cases. In some cases meningitis occurs as the second phase of biphasic illness, suggesting that immune mechanisms may play a pathogenic role. The acute illness ordinarily lasts for 3 – 10 days. The mortality is 5 to 10 %.

Laboratory diagnosis

1.  Microscopic examination: A diagnosis based on direct microscopic examination of blood should be made. Demonstration of leptosires in fluid by dark-ground microscopy and tissues by FAT is helpful in diagnosis of the infection. The test is particularly useful in detecting urinary shedders. Tissue speicimens can also be stained by silver impregnation staining technique to demonstrate leptospires.
2.  Isolation of leptospira: Blood or CFS collected during acute illness or urine after one week of clinical illness and tissue material obtained on autopsy are used for bacteriological isolation of leptospira.
3.  Serological tests: Serum antibodies usually appear during the second week of illness and reach maximum titre during the third or fourth week. A number of serological tests may be done with suspensions of killed leptospira containing the most common antigenic strains for detection of illness, e.g., slide  agglutination, microscopic plate and capillary tube agglutination, complement fixation and microscopic agglutination tests.

4.  Molecular diagnosis like PCR may be performed for rapid and accurate diagnosis.

Control and prevention: Protection of occupationally exposed population by providing protective clothings, viz. gumboots, gloves, etc. when working in field, mines, sewers, harvesting sugarcane and rice, cleaning of pig-pens, cow shed, kennels, etc. Animal sheds should be proofed of rats and the floor should be washed regularly with a sodium hypochloride solution. Rodent control in rural and recreational areas of human habitations, sugarcane field, rice field, etc. Health education particular to occupational exposed population about the modes of transmission, avoidance of use of contaminated sources of water and the need for use of protective clothings. Immunization of population at risk and the pets animals, particularly dogs with
prevalent dominant local strains to prevent clinical illnesses.

Posted Date: 9/20/2012 2:25:33 AM | Location : United States

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