Leptospirosis

Leptospirosis

Leptospirosis (“Lepto”) is a worldwide zoonotic disease caused by pathogenic Leptospira bacteria. It can affect nearly all mammals and range from an unnoticed infection to severe illness, organ failure, or death. The bacteria are aerobic, gram-negative spirochetes with a corkscrew shape.

Hosts, reservoirs, and transmission

• Leptospirosis is most often recognized in cattle, swine, dogs, and horses. Cats appear relatively resistant to clinical disease, though exposed cats may develop antibodies.
• Maintenance hosts commonly have mild or subclinical infections. The bacteria can persist in their kidneys and genital tracts, allowing them to shed Leptospira in urine for months or even years and act as reservoirs.
• Incidental hosts, including people and many domestic animals, are more likely to develop acute illness. They generally shed the bacteria for a shorter period.
• Infection spreads between maintenance hosts through infected urine, placental fluids, or milk, and sometimes through mating or across the placenta. Incidental hosts are most often infected indirectly through water contaminated with infected urine.
• Warm, moist conditions favor survival and transmission. Freezing, drying, and sunlight kill the bacteria. Disease is more common in warm, wet climates and may be seasonal in temperate regions.
• Wildlife such as rodents, raccoons, opossums, and skunks can maintain infection and expose domestic animals or people. Vaccination has reduced some historically important canine serovars, while infections from wildlife-associated reservoirs remain a concern.
• People may be exposed through work with animals or recreational contact with contaminated water. Animal body fluids can also expose owners and veterinary or farm workers.

How infection causes disease

After entering through mucous membranes or damaged skin, Leptospira circulate in the blood and multiply in tissues. Following an incubation period of about 4–20 days, the bacteremic and tissue-colonization phase lasts roughly 7–10 days. Antibodies then help clear the bacteria, though damage to organs may take longer to resolve. Severe damage can lead to chronic illness or death.

In incidental hosts, acute disease commonly includes fever and kidney and/or liver damage. Other possible effects include uveitis, pancreatitis, bleeding, hemolytic anemia, muscle pain, and respiratory disease. Human illness can also range from mild or symptom-free infection to multiple-organ failure; reported signs include fever, rash, headache, eye and muscle pain, and weakness. Infection during pregnancy or breastfeeding is a concern because transmission to the fetus or infant can occur.

Biosafety

When leptospirosis is a possible diagnosis, the video advises handling animal fluids with gloves and wearing a gown and shoe covers. Face protection is recommended when handling wet bedding or cleaning cages because the bacteria may become aerosolized.

Diagnosis

Diagnosis begins with a thorough clinical and vaccination history. Tests may detect antibodies or the organism itself.

• Microscopic agglutination test (MAT): The commonly used animal antibody test. Live Leptospira are mixed with diluted serum; the reported titer is the highest dilution that produces 50% agglutination.
• ELISA: Detects antibodies to a membrane protein of pathogenic Leptospira. It gives a positive/negative result, but may also detect antibodies from vaccination; semi-quantitative in-hospital versions are available.
• Interpreting antibody results: Interpretation can be complicated by cross-reactions, prior vaccination, and disagreement about what titer indicates active infection. Vaccine-associated titers are often relatively low and may last several months. With compatible signs and vaccination more than three months earlier, a titer around 1:800–1:600 can provide good presumptive evidence of infection.
• Paired samples: Comparing an acute sample with one collected later—often 7–10 days afterward—can help. A fourfold rise in titer is often seen in acute infection.
• PCR and tissue testing: PCR can detect pathogenic Leptospira in blood, urine, or tissue, but does not identify the serovar. Immunofluorescence may be used on urine sediment or tissue; its sensitivity in fixed tissue depends on how many organisms are present.
• Culture: Slow and difficult, so more commonly used in research. It is the only method described in the video that definitively identifies the infecting serovar.
• Timing of samples: Blood may test positive by culture or PCR early in disease; urine is more likely to be positive about 7–10 days after clinical signs begin.

Prevention and treatment

• Avoidance alone is difficult for domestic animals because wildlife reservoirs are common.
• The video identifies polyvalent inactivated vaccines as the preferred prevention for domestic animals and says vaccines are available for dogs, cats, cattle, and horses. For people, avoiding potentially contaminated water is the main preventive measure described.
• Treatment varies by species:
  • Dogs: A two-week course of doxycycline is preferred. Penicillin may be used initially if doxycycline is not tolerated; doxycycline is ultimately recommended to clear the renal carrier phase.
  • Horses: Tetracyclines and penicillin have been used, as have enrofloxacin and aminoglycosides.
  • Ruminants and swine: Drugs used include tetracycline, oxytetracycline, penicillin, ceftiofur, tilmicosin, and tulathromycin. Oxytetracycline is recommended to eliminate the renal carrier state.

The central takeaway is that vaccination helps prevent disease in domestic animals, while appropriate antimicrobial treatment is important in acute cases and tetracyclines are recommended for clearing persistent renal infection.

Speakers and sources

• Speaker: One unnamed narrator presenting the material for VetMed Academy.
• Source/presenter: VetMed Academy. The video metadata also credits collaboration with the MSD Veterinary Manual.