Leptospirosis in small animals
ORLANDO, FL – Leptospirosis is an infection that can affect animals and humans that come in contact with Leptospira bacteria. It is considered a zoonotic disease, commonly transmitted to humans via water contaminated by animal urine coming in contact with wet or broken skin, or with the mucous membranes, explained Liza Wysong Rudolph, BAS, LVT, VTS (CP – Canine/Feline), speaking at the North American Veterinary Conference.
Leptospira are aerobic gram-negative motile spirochetes of which there are over 250 pathogenic serovars or subtypes. The primary pathogenic species in the dog are Leptospira interrogans and Leptospira kirschneri. Reservoir hosts remain asymptomatic or develop mild self-limiting symptoms when infected. Leptospira is most viable in warm, moist conditions, and survival in the environment may be prolonged in stagnant or slow moving water. Although the organism can remain viable in the environment for months under ideal conditions, replication only occurs within a host.
Etiology
Animals can become infected through direct contact with infected urine, venereal, placental transfer, bite wounds, or ingestion of infected tissues. Indirect transmission is the more common route and can occur through exposure to contaminated water sources, soil, food, or soiled bedding. Evidence of leptospirosis exposure has been documented in cats; however, clinical disease has been rarely reported.
After penetrating the skin or mucous membranes, leptospira quickly multiply in the bloodstream, with an average incubation period of approximately 7 days, after which the organisms attach to endothelial cells and spread throughout the body. The kidneys, liver, spleen, eyes, genital tract, and central nervous system are all commonly affected.
Clinical signs
Clinical signs can be variable and are often dependent on the infecting strain, individual immune response, and organs and tissues affected. Early findings are often vague and non-specific and include fever, depression, lethargy, anorexia, myalgia, and oculonasal discharge. Vomiting, diarrhea, dehydration, hematuria, and petechia/ecchymosis may develop as the disease progresses. Most patients are in some degree of renal failure, and swollen and painful kidneys may be apparent on abdominal palpation. Polyuria and/or polydipsia are often noted, which may progress to oliguria or anuria. Icterus is usually present in patients suffering hepatic injury. Renal, hepatic, pulmonary, vascular, and hematologic abnormalities are common and acute lung injury, meningitis, vasculitis, coagulopathy, and disseminated intravascular coagulopathy can be seen in some cases.
Symptoms in people range from self-limiting, flu-like symptoms to rapidly fatal disease, with a reported incubation period of 2-25 days. Most people have mild infections, with signs such as fever, headache, chills, muscle aches, vomiting, transient rash, and jaundice. However, approximately 10% of infected people have complications such as hepatic failure, renal failure, aseptic meningitis, hepatic dysfunction, myositis, and uveitis. Ms. Rudolph stressed that humans are also susceptible to multiple serovars, and immunocompromised individuals, children, and the elderly are at greatest risk.
Diagnostics
A CBC may reveal neutrophilia, lymphopenia, anemia, and/or thrombocytopenia. Elevated blood urea nitrogen and creatinine is present in most patients. Hepatic injury may be evidenced by increases in alkaline phosphatase (ALP), alanine aminotransferase (ALT), aspartate aminotransferase (AST), and bilirubin. Electrolyte abnormalities such as hyponatremia, hypochloridemia, and hypokalemia may be seen, but in patients with oliguria and anuria, hyperkalemia can be present. Urinalysis may reveal glucosuria, proteinuria, granular casts, isothenuria, hematuria, and bilirubinuria.
Patients with respiratory involvement or vasculitis may have abnormal thoracic radiographs and abdominal radiographs may reveal liver, spleen, and/or kidney enlargement. Ultrasonography of the abdomen may be particularly useful in these cases for further defining organ architecture and renal abnormalities.
The most common serologic test for leptospirosis is the microscopic agglutination test (MAT). A positive titre of 1:800 or greater in a non-vaccinated dog with clinical signs is compatible with leptospirosis. Negative test results are common during the acute phase of infection (approximately the first 7-10 days) and these patients should have a follow-up test 2-4 weeks after the first titre. A fourfold increase is considered diagnostic for leptospirosis.
A PCR assay can be run on serum or urine to detect the nucleic acid of leptospires. Negative results do not rule out leptospirosis as a low number of organisms in the sample can skew the results. Although leptospires are initially more prolific in the blood, as the disease progresses a greater number will be found in the urine. Often it may be optimal to submit blood and urine samples simultaneously for PCR testing to decrease the likelihood of false negative results. PCR samples should be obtained prior to any antibiotic administration as false negatives can occur. Ms. Rudolph notes that culture is not recommended as leptospires are difficult to grow and false negative results are not uncommon.
Treatment
According to the 2010 ACVIM Small Animal Consensus Statement, doxycycline (5 mg/kg PO or IV q12h for 2 weeks) is recommended, and treatment should begin before receiving finalized lab results. If doxycycline is not tolerated, ampicillin at a dose of 20 mg/kg IV q6h (dose reduction is recommended for azotemic pets) should be administered. However, doxycycline should be instituted once gastrointestinal signs have subsided in order to eliminate a carrier state. Reversal of tissue injury caused by the organism is more likely if treatment is initiated earlier in the disease process.
In order to address dehydration and electrolyte imbalances, IV fluid therapy, anti-emetics, and supportive care are routinely necessary in these patients. Patients with hypoalbuminemia or DIC may require the administration of blood products.
Hospitalization considerations
Due to transmission potential to people and other mammals, all dogs with acute renal failure should be handled as leptospirosis suspects until proven otherwise. Hospital staff should use protective equipment during patient handling, and hospitalized patients should be housed separately from other animals. Leptospires are sensitive to many disinfectants (such as 1:1 dilution of 10% bleach, iodine based disinfectants, quaternary ammonium solutions, and accelerated hydrogen peroxide) and drying. Cages and runs must be disinfected routinely and urine leakage and run-off must be avoided. Pressure washing is not recommended to clean kennel areas since aerosolization of leptospires can occur. Soiled bedding can be cleaned via normal laundering techniques.
Patients with suspected leptospirosis should not urinate in areas frequented by other dogs, and urine should be collected and disposed of to minimize accidental exposure. Disinfection can be accomplished with a 10% bleach solution. When manipulating urinary catheters or collection systems it is important that goggles and a mask or full-face shield be worn. All bodily fluids and tissues of leptospirosis patients should be considered medical waste and be disposed of appropriately. Upon patient discharge owners should be notified to wear gloves and wash hands if there is a possibility of contact with their dog’s urine until antimicrobial treatment is complete. In the unfortunate occurrence of patient death, any individuals handling the body should be alerted of the potential zoonotic risk.
Vaccination and prevention
Leptospirosis vaccine is generally considered a non-core vaccine and should be administered to dogs at increased risk. The newer quadrivalent type includes the following serovars: Canicola, Icterohaemorrhagiae, Grippotyphosa, and Pomona. Bivalent vaccines (Canicola and Icterohaemorrhagiae) are still available, but not recommended as they are not cross-protective against other serovars. Leptospirosis vaccines offer protection for at least 12 months. Initial immunization series involves 2 to 3 injections with each injection administered 2 to 3 weeks apart. Current data indicates that there is no greater risk of acute vaccine reactions associated with leptospiral antigen vaccines versus other vaccines for dogs.
Ms. Rudolph concluded by saying that although exposure to livestock and wildlife has been reported as a risk factor, dogs in urban areas are also at risk through contact with infected rodents and their urine. There is typically an increased incidence of leptospirosis in late summer to fall, especially during flooding or heavy rainfall. Control of rodent population, decreasing access to potential sources of infection (e.g. stagnant water), and isolation of infected animals can help to prevent spread infection.CVT