CANINE LEPTOSPIROSIS-AN UPDATE

INTRODUCTION

It is also known as Canine typhus, Stuttgart disease, Wiells disease, Infectious jaundice, Rice field workers disease, Swine handler’s disease. Leptospirosis is a contagious disease caused by a family of organisms known as Leptospira interrogans sensu lato. Several antigenically distinct serovars of L. interrogans sensu latu are responsible for disease in dogs (L. canicola, L. icterohaemorrhagiae, L. grippotyphosa, L. pomona L. bratislava and L. autumunalis). Leptospirosis is a zoonotic disease of worldwide veterinary significance in numerous animal hosts, including the dog as well as in human. In canine, disease present as an acute infection of the kidney and liver and, sometimes as a septicemia. Chronic kidney disease is a common sequel of infection and abortions may occur in pregnant dams. Over the past 30 years, preventive vaccination against two of the most common leptospires, L canicola and L. icterohaemorrhagiae, have nearly eradicated clinical disease associated with these strains among the inoculated population. Until recently, vaccines were available for only two strains (L. canicola and L. icterohaemorrhagiae), but vaccines for two additional types (L. grippotyphosa and L. pomona) are on the market. Controversy arises because some dogs are allergic to the carrier in the leptospira vaccine; as result, some veterinarians no longer use the inoculant in areas where the disease is not a problem.

Leptospires are known as “aquatic spirochetes”; they thrive in water and appear long and helical with a characteristic hook on one or both ends. As recent as the 1980s, L. icterohaemorrhagiae and L. canicola were identified as the most prevalent serovars causing leptospirosis in the canine. By the 1990s, however, an increased incidence of L. grippotyphosa and L. Pomona was observed in conjunction with a resurgence of leptospirosis disease suggesting a changing trend in the epidemiology of this disease. It is speculated that these changes in serovar prevalence are related to two primary factors that may strongly influence the epizootology of leptospira serovars. These factors are-a) preventive vaccination has all but eradicated clinical disease in the domestic dog and b)there has been an increased migration of wild life, for which serivar infections with L. grippotyphosa and L. Pomona are more prevalent, into suburban areas. Leptospirosis has a seasonal distribution and is most prevalent in late summer to fall. Rainfall can be used to predict the occurrence of leptospirosis. Leptospira organisms do not multiply outside of the host animal species, but they survive well in the environment under optimal conditions. Leptospira thrive in spring and autumn when wet soil conditions and moderate temperatures support their otherwise poor environmental survivability. 

TRANSMISSON

Transmission of leptospira takes place through direct contact with the urine of infected animals or ingestion of urine contaminated water or food. Human or animals may contract infection through flood or while swimming in contaminated water and by inhalation. Leptospira organisms may enter the animals body through abraded skin, mucous membrane or conjunctiva. 

PATHOGENESIS

An understanding of the pathogenesis of leptospirosis is incomplete. The animal host acts as a reservoir shedding the organism intermittently and passed in urine. Initially, leptospires penetrate the mucus membranes or intact or abraded skin. Then, over the next 4 to 11 days, organisms rapidly invade the blood stream, creating a leptospiremia leading to fever, joint pain, general malaise, transitory anemia due to hemolysis, leukocytosis, haemoglobinuria and albuminuria. In susceptible dogs, leptospires usually establish a septicemia and spread systemically to the internal organs, including the liver, spleen, kidneys, central nervous system, eyes, placenta and fetus. Thereafter, increases in serum antibodies clear the spirochetes from most organs, but organism may persist in the kidneys and be shed in urine for weeks to months. The extent of development of specific lesions or damage depends on the particular serovar and its virulence as well as dogs immune status, younger dogs (<6 months) seem to develop more signs of hepatic dysfunction in an outbreak of leptospirosis; however, acute renal failure in young dogs is often associated with L. grippotyphosa. The edema and disseminated intravascular coagulation may occur in rapid and severe leptospirosis that result in acute endothelial injury and haemorrhage. Leptospira lipopolysaccharide stimulates neutrophil adherence and platelet activation, which may precipitate inflammatory and coagulation.

Most characteristic lesions are seen in kidneys. The changes in the kidneys are attributable to the action of leptospiral toxin or toxin along with bile salt. The changes are in the form of haemorrhage, edema and necrosis. Between 90 to 95% of current cases of leptospirosis present clinically as a renal disorder only, both renal and hepatic disorders, or a hepatic disorders only. The liver is the second most major parenchymatous organ damaged during leptospiremia. The degree of icterus in both canine and human leptospirosis is usually corresponds to the severity of hepatic necrosis.

CLINICAL SIGNS

The severity of clinical signs is influenced by a dogs age, vaccination status, virulence of organism, environmental factors as well as route and degree of exposure. The signs in dog appears as per-acute, acute, sub-acute and chronic. During the first 4 to 12 days following infection with leptospira, the typical symptoms are fever (103-105°F), depression, loss of appetite, joint pain, dehydration, diarrhea, vomiting, nausea, excessive drinking, jaundice and excessive bleeding due to mainly involvement of liver and kidneys. 70% of the cases caused by L. icterohaemorrhagiae and 50% are caused by L. canicola. In per acute to sub acute diseases dogs may die without clinical signs. 

CLINICAL PATHOLOGY

In most cases of leptospirosis there is thrombocytopenia, leukocytosis and neutrophilia with a left shift. The parameters measured in the assessment of kidney function are called “Blood urea nitrogen” (BUN normal levels are around 25 mg/dl) and “creatinine” (normal levels are around 2.0 mg/dl). On the basis of severity of infection lesions can be divided into “mild to moderate” group having an initial BUN level ranging from 24 to 225 mg/dl and initial creatinine level between 1.7 to 11.5 mg/dl and “moderate to severe” group having an initial BUN level ranging from 97 to 365 mg/dl and initial creatinine levels ranging from 6.5 to 21.9 mg/dl. The BUN and creatinine are increased due to the renal failure. Electrolyte levels vary according to the degree of renal failure. There may be increase in ALT, AST, ALP and bilirubin due to liver damage. Urine analysis may reveal increased protein and bilirubin. 

DIAGNOSIS

1. Diagnosis of leptospirosis is based on a combination of suggestive historical information, physical findings, nonspecific laboratory findings, and confirmatory testing.
2. confirmatory tests include serological testing to detect antibody production to leptospira. The current “gold standard” diagnostic test for leptospirosis is the Leptospira Microscopic Agglutination Test (L-MAT) performed during the acute stage of disease.
3. Direct detection of leptospira-

a)      Dark field microscopy versus fluorescent antibody testing of urine- often the dark field examination of urine is inconclusive. It is difficult to read, and require fresh urine in order to observe intact leptospiral cells.

b)      Fluorescent Assay (FA)- fluorescent examination of centrifuged urine sediments is a more definitive test and leptospira do not need to be viable.

c)      Culture- antemortem culture of body fluids (urine, blood, aqueous humor) and postmortem culture of tissues (kidney, liver, fetus, placenta) is usually not practical due to the fastidiousness of leptospires.

d)      Polymerase chain reaction (PCR)- with the advent of PCR tests, rapid and genus and serovar specific detection of leptospiras from clinical specimens should be possible.

e)      Histopathology- special stains like Warthin-Stary silver stain, and immunohistochemistry, using monoclonal antibodies, should be attempted on formalin-fixed sections of kidney, liver, fetal and placental tissues.  

TREATMENT

The aims of treatment for acute cases of canine leptospirosis are to control the infection before irreparable damage is done to the liver and kidneys, and to suppress the leptospiruria.

1. Antimicrobial therapy-
   1. Drug of choice Penicillin (Procain penicillin G) and its derivatives (Ampicillin anf amoxicillin).
   2. Dihydrospreptomycin, Tetracycline, Doxycycline and Erythromycin .
   3. Aminoglycosides can not be used in patients until kidney function has been restored.

2.  Fluid therapy-

Intravenous fluids therapy are crucial to support blood flow through the damaged kidneys so

that recovery is possible.

3.  Antiemetics-

Vomiting is frequently severe with leptospirosis, and antiemetics (Metaclopramide

Chlorpromazine) may be used.

Patients survival rates as high as 80 to 90% has been reported in dogs following with traditional

medical management or medical treatment with concurrent hemodialysis.

PREVENTION AND CONTROL

1. All possible measures should be taken to avoid leptospires contamination made by the excreta of domestic and wild carrier animals.
2. Owners should be advised that leptospirosis is a zoonotic disease that is spread mainly by the urine of infected dogs.
3. Veterinary clinicians and staff should wear protective latex gloves when handling any dog with possible leptospirosis as well as blood and bodily fluids from animal.
4. An infected dogs housing and outside areas need to be treated with a suitable disinfectant i.e. iodine based disinfectants.
5.  Dogs should avoid muddy, stagnant water and rodents.
6. Control exposure of animal to wildlife, cattle or other reservoirs or eliminate rodents.
7. Rodents are the main carriers of leptospirosis. According to WHO rodent control and effective improvement of sanitation are the important aspects of control.
8. Vaccination- For over two decades, typical bacterins were designed to protect dogs from L. canicola and L. icterohaemorrhagiae. However, these products did not provide protection from infection by other reservoirs.

Fort Dodge Animal Health now offers the Duramune leptospirosis vaccine that immunizes against L. grippotyphosa, L. pomona, L. canicola and L. icterohaemorrhagiae. Leptosprosis containing vaccines are associated with a higher risk for side effects, particularly anaphylactic reactions. Leptospirosis vaccines may only protect dogs for 6 to 8 months, so veterinarians in high risk areas recommend twice yearly vaccination.

Back