There has been quite a stir in the Spinone world recently about a disease named Leishmaniasis (pronounced LEASH-ma-NIGH-a-sis). What exactly is this disease? Is it something new and can it affect humans or is it limited to the canine world?
What is it? Leishmaniasis is a parasitic disease spread by the female phlebotomine sandfly. There are three different clinical forms of the disease, cutaneous Leishmaniasis (CL, often referred to as “oriental sore”), mucocutaneous Leishmaniasis (ML) and visceral Leishmaniasis (VL, often referred to as “kala-azar”). All three forms are transmitted to humans and dogs by the same kind of sandfly. While CL and ML are fairly treatable, VL, if not treated, can be fatal.
What are the symptoms? Symptoms of CL include primarily sores on the skin; sometimes single sores and sometimes multiple sores. The sores usually have a raised edge and a concave middle, some sores scab over. If the sore is near a gland (e.g. under or on the arm) the glands may swell. Fever, weight loss, loss of appetite, and an enlarged spleen and liver usually identify VL. Blood tests usually return a low blood count including low red blood cells, low white blood cells and low platelet counts. Symptoms are usually noticed from within weeks of acquiring the disease (in CL cases) to several months or even several years (in VL cases) as the disease can remain dormant for long periods of time. Leishmaniasis can be difficult to diagnose because the clinical signs are not specific to the disease and, when present, can be very mild for long periods.
Where did it come from? Leishmaniasis is an ancient disease, evidence of which is found in many parts of the tropical and arid world, dating back over a millennium ago. Today forms of this disease can be found in at least parts of 88 countries meaning approximately 350 million people worldwide are at risk. The northern edge of this disease’s range in the western hemisphere appears to be Texas or Oklahoma. According to a May 2000 Center for Disease Control report it is very unlikely a person will contract Leishmaniasis in the United States (or Canada for that matter). There have been a few reports of CL in rural areas of southern Texas, but that is the only kind of Leishmaniasis ever reported in the United States. No cases of VL are known to have been acquired in the United States. According to the CDC there are roughly 1.5 million new cases of CL reported each year and 500,000 cases of VL reported annually.
Of course all of these reports deal with human contact with the disease. What about the disease in dogs? According to the Merck Veterinary Manual, VL in dogs is prevalent in Central and South America, the Middle East, Asia and the Mediterranean region. As of 1998 several foci (identified starting points of a disease) have been described in the United States; these being in Texas, Oklahoma and Ohio. By mid-2000 researchers and public health authorities indicated they had discovered that hunting dogs in 21 states were infected with the parasite that causes VL. The Merck Manual also points out that, while dogs, like humans, can be fully affected by the disease, cats and other domestic animals are rarely infected and usually only develop cutaneous (skin) ulcers without showing any other signs of VL. Just like with humans, the parasites are transmitted by phlebotomine sandflies, which are found worldwide, according to the Merck Manual. The flies, however, do not range very far, completing their life cycles in an area less than 1 km in diameter. The incubation period in dogs is quite variable and is much like that in humans, ranging from 3 months to 3 years or more. The most reliable test for canine Leishmaniasis is direct observation of the parasite in bone marrow or lymph node smears. Serologic test methods are available, but are not as reliable as direct observation. There are some treatments available for dogs, but they are expensive and relapses after treatment are common.
Is Leishmaniasis something to be concerned about? Like any new disease there is cause for concern. None of the experts, however, are claiming that the disease is going to run through the U.S. human or dog population like a hot knife through butter. It is important to remember that this disease is still very rare in the U.S. The sandfly is assumed to be the carrier of the disease in the U.S., however, because the sandflies in the U.S. are a number of different species from the sandfly in endemic regions, it is not clear which species carries the disease.
I recently asked Dr. Edward Breitschwerdt of the College of Veterinary Medicine at North Carolina State University in Raleigh, an expert in tick-borne infections and a leading researcher in Leishmaniasis, a few questions regarding Leishmaniasis and how it is spread. It appears that one of the species of sandflies native to the U.S. is the most likely source of infection. At this point it is not known which species is the most likely carrier. According to Dr. Breitschwerdt the disease cannot be spread by dogs drinking from a common water bucket, nor is it likely to be spread during a dogfight. It is possible that an infected dog, with oral ulcers at the time of the fight, could pass the parasite on, however this would be an inefficient means of transmission. It is also highly unlikely that a male dog would pass the parasite to a female during breeding. It is possible, but the female would have to have a cut or open wound in the reproductive tract. Transmission via ticks, mosquitoes and fleas, while not completely ruled out, is not thought to be likely (E. Breitschwerdt, personal communication, May 11, 2001).
What about a vaccine? While there is no vaccine available at present, progress is being made on a vaccine for humans. According to a study from Columbia, a successful trial using a killed Leishmania amazonesis vaccine (a western strain, not the Mediterranean strain) has been concluded. This double-blind trial was done by researchers from the University of Antioquia using four vaccination groups totaling almost 300 individuals. The study was published in the journal Transactions of the Royal Society of Tropical Medicine and Hygiene, 94, (6), 698-703, and recommends a phase III efficacy trial be started.
References
Aiello, S. (Ed.). (1998). Visceral Leishmaniasis. In Merck Veterinary Manual (pp. 566-567). Whitehouse Station, NJ: Merck & Co., Inc.
Allison, M.J. (1993). Leishmaniasis. In Cambridge World History of Human Disease (pp. 832-834). New York: Cambridge University Press.
Center for Disease Control. (2000). Leishmania infection. Retrieved May 9, 2001 from the World Wide Web:http://www.cdc.gov/ncidod/dpd/parasites/leishmania/factsht_leishmania.htm
Enserink, M. (2000, December 8). Has Leishmaniasis become endemic in the U.S.? Science, 290, 1881+.
Marble, M. (2001, February 14). Killed vaccine deemed protective in clinical trial. Vaccine Weekly [Online], 10 pars. Available: Information Access/Expanded Academic Index/1070197101 [2001, May 9].
"Leishmaniasis" was originally published in the newsletter Heartbeats (ISSN 1094-1924), v.5, n.1, Spring/Summer, 2001, and is copyrighted by Kevin McGrew ©2001. Use of this article, beyond what is legally considered "fair use," without the permission of the author, is prohibited by Federal Copyright Law.