Visceral leishmaniasis is an infection of dogs, other animals and humans that causes widespread disease and many deaths in parts of Asia, Africa, South America and southern Europe. Where it occurs dogs are seen as a "reservoir" of infection for humans. Until recently, cases of leishmaniasis in dogs diagnosed in the U.S. (rare) had occurred in dogs that had been born or resided temporarily in southern European or South American countries where the infection is transmitted by sand flies. Visceral leishmaniasis had not been considered to be established in North America, however, recent events indicate that it does occur in foxhounds and perhaps certain other breeds of dogs. Foxhounds appear to have been infected with a strain of the parasite that originated in southern Europe. The Spinone breed is at risk of the infection because many dogs of this breed have been directly imported from Italy where the infection is present. Leishmaniasis is generally believed to be transmitted via the bites of sand flies; however, this method of transmission has not been confirmed in North America and it is suspected that the infection is transmitted from dog to dog in blood and secretions incidental to biting, licking, breeding, blood transfusion, etc. We believe that it is very important to determine the exact modes of transmission of the infection in order to be able to control it and, ultimately, eliminate it from dogs in North America. There is concern that this infection could spill over into the human population; however, there is no evidence that this has yet occurred. This is why the Centers For Disease Control and Prevention (CDC) and state public health scientists are assisting in this investigation.

The signs of leishmaniasis in dogs are variable and often do not appear until many months after exposure to the infection. Most veterinarians in the U.S. have never diagnosed a case of this infection and may be unfamiliar with the condition. The infected dog may lose weight and develop swollen lymph nodes or anemia. Skin lesions are common including hair loss and ulcers. The dog may lose appetite, become lethargic and bleed from the nose. Without treatment most infected dogs ultimately die. Medical treatments (allopurinol, antimonial compounds and other medications) can improve condition and prolong survival but rarely eradicate the infection.

Considerable care should be used by persons who come into close contact with infected dogs. Human infection acquired as a result of direct exposure to an infected dog has never been reported, however, humans are potentially susceptible and precautions should be taken to avoid direct contact with blood and secretions of known infected animals. Special precautions should be taken with young children and persons with deficient immune systems when in contact with these known infected animals, i.e., such contact should be limited and strictly supervised. CDC has agreed to work with dog owners to investigate this problem; these investigations will include testing of dogs for serum "antibodies" indicative of exposure or active infection with the organism. The test performed at CDC is called the indirect immunofluorescence test and is just one tool to make the diagnosis. It detects antibodies in the blood that are stimulated by the presence of the parasite. The intensity of the titer reflects the stage of the infection and the response of the animal to the infection. In general, the antibody titer increases (from 1:16 to 1:512 or greater) as the infection progresses. Questions have been raised concerning interpretation of the titers of the dogs and disposition of positive hounds, e.g., "What is positive?" and "What should we do with a positive animal?" At this point in our understanding of this infection in dogs, we recommend the following:

Any dog with a Leishmania-positive serum titer of 1:16 or higher should be considered "possibly infected." Additional serodiagnostic testing will be needed to detect if further elevation of the antibody titers has occurred.

Any dog with a titer of 1:64 or higher should be considered "highly suspect" and should be subject to further diagnostic examinations to include biopsy of bone marrow, spleen, lymph nodes or open skin sores in order to isolate and culture the Leishmania or to confirm its presence with a test for DNA called PCR (Polymerase Chain Reaction). Positive results of these tests confirms the presence of the infection; however, negative results in these tests in a dog with a positive blood titer cannot completely rule out active infection because the specimen that was examined might not contain the infective organism.

Most infected dogs with medium to high titers (1:64-1:512) do not show symptoms of the disease, in fact they may appear quite vigorous and healthy. Even though they appear healthy we believe that they are capable of shedding infectious organisms resulting in transmission to other animals.

Dog owners must be aware that the results of blood testing may not be absolutely accurate in detecting infection in dogs. In most animals there seems be a lag time between establishment of the infection and the appearance of detectable antibody. The duration of this "false negative" period is not known precisely but in some animals it may last several months to a year. Whether or not dogs are capable of passing on the infection during this period is not known but there is good reason to believe that they can. Regular antibody screening is probably the best thing that a dog owner can do to ensure that dogs are not infected but the results of tests for antibody, and virtually all other tests, are not 100% sensitive or specific for detecting infected animals. Ideally, dogs originating from a country where this infection exists should be tested at a qualified laboratory before they are imported to this country. It probably would be wise to test imported dogs biannually after they have arrived here for a year or two in order to detect possible seroconversions after arrival. Be aware that there are certain aspects still unknown about this disease in dogs, therefore, answers to many important questions are not yet available.

If dog owners elect to euthanize "seropositive" animals for any reason, or if the dogs should die, the CDC should be contacted for assistance in confirming the infection. Samples of bone marrow, liver, spleen or lymph nodes should be taken by the veterinarian from euthanized animals with titers of 1:64 and higher and sent to CDC or the Walter Reed Army Institute of Research (WRAIR) for culture of the infective organism. Tissue samples from living seropositive dogs can also be collected by biopsy and examined in the diagnostic tests. Please contact us for further instructions on collection of diagnostic specimens or additional information (Telephone: (770) 488-7767). Thank you for your cooperation.

Peter M. Schantz, VMD, PhD
Division of Parasitic Diseases
National Center For Infectious Diseases
Centers For Disease Control and Prevention
Mailstop F22
4770 Buford Highway
Atlanta, GA 30341

Telephone: (770) 488-7767
Fax: (770) 488-7761
e-mail: PSchantz@cdc.gov