Leishmanioses are a group of zoonotic diseases transmitted to humans and animals by the bite of phlebotomine sand flies. The diseases are named after Sir William Boog Leishman, Director General Army Medical Services 1923-1926. Leishmanioses are caused by Leishmania intracellular parasitic protozoans. Worldwide, they are one of the most important vector-borne diseases. Veterinary forms of leishmaniasis are canine leishmaniasis and feline leishmaniasis. There are at least 20 species of Leishmania. Each may cause a disease specific to the species and the host response. The animals that maintain the parasite (reservoirs of the disease) are canines and rodents (zoonotic cycle) and, in countries such as Sudan, humans (anthroponotic cycle). Leishmaniasis occurs in three forms, known as cutaneous leishmaniasis, visceral leishmaniasis, and mucocutaneous. While a given species of Leishmania typically produces one or the other clinical form, some can produce both.
The incubation period of mucocutaneous leishmaniasisis 1-3 months, but in humans may occur many years after the initial cutaneous ulcer has healed. Mucosal involvement occurs in South American cases of cutaneous leishmaniasis (espundia) involving the nose, oral cavity and pharynx. This causes difficulty with eating and an increased risk of secondary infection which carries a significant mortality.3 Visceral leishmaniasis is also known as kala-azar ("black fever") and dumdum fever. This chronic from of leishmaniasis can be transmitted to animals and humans via sand fly bite and is usually fatal if untreated. The lesions usually occur on the nose and ears. Dogs are also susceptible to visceral leishmaniasis and may be important reservoirs, but cats are rarely infected and usually do not show signs of disease.
Visceral leishmaniasis can be complicated by disseminated intravascular coagulation (DIC), a syndrome characterized by the systemic activation of blood coagulation which generates intravascular fibrin leading to thrombosis in small and medium sized vessels and eventually organ dysfunction. It can be also associated with severe hemorrhaging due to the consumption of platelets and coagulation factors. Several mechanisms can lead to activation of intravascular coagulation, including endotheial damage, platelet activation and release of tissue procoagulants. In canine visceral leishmaniasis, endotheial damage induced directly by Leishmania and the deposition of immuncomplexes appear to play a role in triggering disseminated intravascular coagulation. Thus, dogs naturally infected by Leishmania (Leishmania) chagasi can develop disseminated intravascular coagulation, which seems to be associated with several immunological and pathological mechanisms involved in the disease.5
Treatment of canine visceral leishmaniasis is rarely curative. Prognosis for emaciated chronically infected animals is very poor and in these cases euthanasia should be considered. There is also a potential zoonotic transmission of organisms from lesions to humans while maintaining a Leishmania-infected dog in a household, particularly if there are immunosuppressed people sharing the household. The organism will never be completely eliminated and relapse occurs very frequently requiring retreatment. A secreted parasite antigen-based vaccine has recently been licensed for use in dogs in Brazil.4
Cutaneous leishmaniasis is caused by Leishmania mexicana and occurs in south-central Texas where it is maintained by small rodents, particularly the burrowing wood rat, but also opossums, armadillos, and cotton rats.4 Both domestic dogs and cats are susceptible to cutaneous leishmaniasis. Multiple skin lesions developing at sites of bites progress to ulcers that discharge necrotic material. New areas of the body become involved by extension of the existing lesions or spreading of the parasite through blood and lymph. Lesions caused by L. mexicana often spontaneously heal within 6-12 months leading to a scar and persistent protective immune response. Despite this, due to the ulcerative nature of these lesions, treatment is often implemented to speed healing and prevent secondary bacterial infections.4 Cutaneous leishmaniasis can be transmitted from animals to humans. Papular dermatitis caused by Leishmania infantum, is seen in young dogs, and appears to be a mild disease with restricted parasite dissemination and a good prognosis.6
Dermatitis caused by Leishmania
Source: Copyright © 2014 Lombardo et al.; licensee BioMed Central Ltd.
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- A Handbook of Veterinary Parasitology: Domestic Animals of North America Henry Joseph Griffiths, Medical and Veterinary Entomology Gary Mullen, Lance Durden
- Leishmaniasis. Tonio V Piscopo, Charles Mallia Azzopardi
- Leishmaniasis, An Emerging Disease Found in Companion Animals in the United States. Christine A. Petersen, DVM, PhD
- Disseminated intravascular coagulation in a dog naturally infected by Leishmania (Leishmania) chagasi from Rio de Janeiro. Carla O Honse1, Fabiano B Figueiredo, Nayro X de Alencar, Maria de Fátima Madeira, Isabella DF Gremião and Tânia MP Schubach
- Papular dermatitis due to Leishmania infantum infection in seventeen dogs: diagnostic features, extent of the infection and treatment outcome