B501 - LEISHMANIASIS

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B501 - LEISHMANIASIS 

Nature of the disease
Leishmaniasis is a serious protozoan disease caused by flagellated organisms of the Leishmania genus and transmitted by sandflies. There are three forms of disease:
  • Cutaneous leishmaniasis (CL) due, in the New World, to L. mexicana and L. brasiliensis, L. peruviana, and, in the Old World, to L. infantum, L. major, L. aethiopica and L. tropica
  • Visceral leishmaniasis (VL) due, in the New World, to L. chagasi and, in the Old World, to L. infantum, and L. donovani;
  • Mucocutaneous leishmaniasis (MCL) caused by L. brasiliensis and only found in the New World.
Classification
OIE List B disease
Susceptible species
Wild rodents, wild and domestic carnivores and humans as reservoirs of leishmaniasis.

The most common cycle is between dogs and humans. Rodents seem to play an important role in some areas. Occasionally cats, horses, bears and other wild species may also be involved in the epidemiology of the leishmaniasis.

Humans are susceptible to all Leishamania, whereas dogs are more often affected with L. infantum, L. tropica and L. peruviana.

Distribution
The geographic distribution of the CL disease is Texas, Mexico, Central and South America, India, Pakistan, the Middle East, southern Russia, the Mediterranean coast and Africa.

The distribution of the VL disease is the Mediterranean basin, the Middle East, India, China, Mexico, Central and South America, and Africa.

The distribution of the MCL disease seems to be limited to South America.

Clinical signs 
Dogs 

Unless in Humans, the disease in dogs is viscero-cutaneous.

The cutaneous symptoms are similar to those in humans (see below) and include:

  • Skin ulcers mainly on the face 
  • Hairlessness
  • Dandruff (squamosis)
  • Seborrhoea
  • Excessive long claws

The viscerous form starts with the silent invasion by the Leishmania of the bone marrow, liver and spleen. Later they may show:

  • Emaciation with amyotrophy
  • Leukaemia and anaemia
  • Kidney failure
  • Keratitis
  • Splenomegalia and swelling of all lymph nodes
  • Lameness
  • Progressive deterioration, extreme emaciation and with skin ulcers and eventually death

Humans 

In the cutaneous disease, the primary lesion is a painful ulcer or nodule at the site of infection persisting for several months, with residual scarring. 

Further lesions may develop in skin and mucous membranes. Infiltration by inflammatory cells at the inoculation site supports the growth of the parasite. This progresses into a large area of chronically inflamed granulation tissue. The overlying skin undergoes hyperplasia and then necrosis with spreading ulceration. Metastatic lesions occur with a similar inflammatory reaction.

The lesions may heal, become fibrosed or extend indefinitely to produce considerable disfigurement. Treatment can be difficult.

In the visceral disease there is:

  • Intermittent irregular fever
  • Sweats
  • Enlarged spleen
  • Weight loss
  • Anaemia leading to ascites, oedema,
  • Diarrhoea
  • Secondary infections
  • Dark pigmentation of the skin may occur
  • Gross enlargement of liver and spleen

Without treatment, the case fatality rate is 90%.

Post-mortem findings 
In the dog there is:
  • Emaciation
  • Skin lesions
  • Great enlargement and hardening of the spleen, liver, lymph nodes and kidneys
Differential diagnosis 
In dogs, the differential diagnosis includes:
  • Other dermatitis
  • Leucosis
  • Aspergillus's
  • Tuberculosis
Specimens required for diagnosis 
Blood smears can be taken. However, very few organisms are found in the bloodstream, so this is not very reliable.

Spleen or liver samples should be collected. Other samples include lymph nodes and bone marrow. In live dogs, because the spleen can be difficult to sample, bone marrow can be collected by trephination of one of the long bones.

Definitive diagnosis is achieved by finding the parasite — either the amastigote in stained smears or biopsies, or the motile promastigote in culture. DNA probe are also used in a number of reference laboratories.

Serological tests including ELISA and Indirect Immunofluorescence Antibody test can be useful to detect VL disease.

Skin tests are mostly used to detect human infection.

Transmission   
Leishmaniasis is spread by several sandflies (Phlebotomus spp.). Dogs and other animals act as a source of infection from which sandflies spread it to humans.
Rodents, especially certain species of rats are considered the main reservoir.
Person-to-person, congenital, and blood-borne transmission of visceral leishmaniasis are rare but possible.
Risk of introduction   
Leishmaniasis is most likely to be introduced through the importation, accidental or otherwise, of an infected animal or an infected human.

Whether the disease would establish or not would depend on the presence of suitable insect vectors (Phlebotomus spp.).

Control / vaccines  
In humans, treatment of leishmania infections is by pentavalent antimony compounds, applied locally, or given intravenously. Prolonged systemic treatment may be necessary. The drug of choice is sodium antimony gluconate. 

Alternative drugs for some forms of infection are amphotericin B and pentamidine.

In endemic areas, sandflies should be controlled by spraying dwellings with insecticides. Rodents, which can be an important reservoir should be controlled. Rubbish heaps which are breeding areas for sandflies should be eliminated.

Insect repellents and protective clothing should be used to reduce the risk of sandfly bites.

Dogs should be kept indoors after sunset and infected dogs removed.

Vaccination against L. donovani infection has not proven effective. However vaccination against L. tropica has been useful in protecting children from the disease.

References
  • BUSSIERAS J, CHERMETTE R, Protozoologie In Parasitologie Vétérinaire, Ecole Nationale Vétérinaire D'Alfort, 1992, p 23-29; 122-130.
  • Leishmaniosis, In Merck Veterinary Manual, National Publishing Inc. Eight ed, 1998, Philadelphia, p 566-567
  • Leishmaniose du chien, In Dictionnaire Pratique de Thérapeutique Canine et Féline, Masson, Forth ed, 1997, Paris, p 326-327
  • Office International des Epizooties, 2002
  • SOULSBY EJL, Helminths, LeishmaniosisIn Helminths, Arthropods and Protozoa of Domesticated Animals, Lea and Febiger Inc, 7th ed, 1982, Philadelphia, p 545-55