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Leptospirosis/الأمراض المشتركة، كلية الطب البيطري

الكلية كلية الطب     القسم  الاحياء المجهرية     المرحلة 3
أستاذ المادة حبيب صاحب نهر المزيداوي       5/5/2011 9:23:29 PM

Leptospirosis:
Etiological agent = Leptospira interrogans (a gram -ve, spirochete)
Leptospira bacteria are Gram -ve spirochetes with bent or hooked ends. There are more than 200 "serovars," of Leptospira, but all the pathogenic leptospires are now classified as a single species, L. interrogans. The pathogenic serovars do not replicate outside of an animal host, and human-to-human transmission is rare.Animals are critical to the maintenance of pathogenic leptospires in a given area.
• Specific serovars are "hosted-adapted" to particular reservoir species and generally do not cause disease in those hosts, e.g.:
- L. canicola/dogs
- L. icterohaemorrhagiae/rats
- L. grippotyphosa/voles, raccoons and other small mammals
- L. bratislava/pigs, and rats and other small mammals
• Leptospires can persist in the renal tubules without causing disease, and can be excreted in the urine for very prolonged periods of time. 
- Leptospires evade immune responses while sequestered in renal tubules.
• Rats, dogs, rodents and wide animals are the most common source of infection for humans worldwide.

Leptospirosis in humans:
Leptospirosis in people is known by a variety of names, reflecting the sources of infection, e.g., "rice-field fever" and "cane-cutters fever" (transmission from contaminated water) and "swine herder s disease" (transmission from contact with infected animals).
Leptospirosis cases can occur either sporadically or in epidemics, with an incubation period of ~10 days. Humans are susceptible to infection with a variety of serovars.
• The incidence of disease is highest in tropical areas, especially when heavy rainfall increases risks for waterborne infection and drives rodents into urban dwellings. 
- In 2000, there was a massive outbreak associated with flooding in Thailand in which over 5,000 people were infected and over 180 people died.
• In many cases, infection occurs through mucosal contact with water or soil contaminated with the urine of infected animals. Such contact may occur through outdoor jobs, or just recreational activities, e.g., swimming in contaminated waters.
• Veterinarians, farmers and abattoir workers are at particularly increased risk for infection from contact with contaminated urine. 
- Veterinarians and veterinary technicians should handle even routine urinalysis specimens as if they contain leptospires, taking precautions such as gloves and a face shield (to prevent mucosal splashes). 
- The major risk factors above and beyond pig contact were smoking and drinking beverages while working with the pigs; hand washing was protective. 
- Other occupations at risk include sewer workers, members of the military, and rice and sugar cane plantation employees.

Human infections with Leptospira:
Human infections with Leptospira begin, after an incubation period of 7-12 days, with fever and "flu-like" illness. Patients may then develop intense headaches, severe myalgia, abdominal pain, nausea, diarrhea, and sometimes rash, conjunctivitis and conjunctival hemorrhage.
"Weil s disease" (icteric form)
This is the name for the classic hepatic and renal form of leptospirosis in humans, which is most often due to infection with serovar L. icterohaemorrhagiae. The clinical presentation may begin as described above for the anicteric form, but subsequently include:
• petechiae
• hepatomegaly and jaundice 
- The jaundice is primarily due to hepatocellular dysfunction rather than fulminant hepatic necrosis.
• renal tubular damage >>> renal insufficiency 
- The renal insufficiency follows renal tubular damage due to hypoxia or a direct toxic effect of the leptospires.
Recovery can take months and mortality can approach 20% if liver/renal compromise is not treated aggressively.

Leptospiral meningitis: Aseptic meningitis can occur as a sequelae of either Weil s disease or an icteric leptospirosis. The meningitis is thought to be immune-mediated, since the organism is generally not present in the CSF by the time clinical signs develop.
Leptospiral Pulmonary hemorrhage: This illness begins following a period of substantial flooding. Specific risk factors for infection included walking in creeks, having household rodents and owning dogs with Leptospira titers >400.
• The unique feature in these cases was a syndrome of pulmonary hemorrhage. This is a rare manifestation of leptospirosis.

Leptospirosis in animals:

Cattle:
• A common manifestation of Leptospira infection in cattle is abortion. The abortions occur most often in the 3rd trimester, and the fetuses are generally autolyzed and icteric when expelled. 
- 30% of cows re-abort during the next pregnancy. 
- Stillbirths, birth of weak calves and significant drops in milk production can also accompany Leptospira infections.
• Along with reproductive tract disease, occasional cows will show evidence of systemic disease with fever, icterus and hemoglobinuria. 
- Multivalent (including multiple serovars) vaccines are used.

Horses:
• The most common manifestation of Leptospira infection in horses is recurrent uveitis ("moon blindness"). This typically develops 12 months after infection and is an immune-mediated disorder. It has been suggested that the basis for this immune reaction is antigenic cross-reactivity between Leptospira protein and a protein in the equine cornea. 
- These data suggest that horses with recurrent uveitis also have long-term persistent infections with the Leptospira bacteria in their eyes.
• Leptospira infection has also been suggested to be a cause of abortion in horses. For this reason, some horse breeders are using the cattle vaccine in horses. 
- The horses are seropositive to Leptospira, and the fetuses have histopathologic lesions and silver-staining organisms in tissues consistent with Leptospira, but the organism has not been recovered in culture.

Cats: Leptospira infection and disease are very rare in cats.

Diagnosis of Leptospira infection in animals:
• darkfield microscopy of urine -- but absence of the organism does not rule-out infection.
• culture (or FA, PCR or Ag-capture ELISA identification) of the Leptospira organism in blood (early in the course of disease) or urine (later in the course of disease). 
- It is important that culture samples be collected prior to initiating antibiotic therapy! 
- Routine urine culture should also be conducted. 
• histopathology (silver staining for the organism in tissues)
• serology (microscopic agglutination test. MAT most commonly)


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