Leishmaniasis

In Spain there are basically two types of leishmaniasis, depending on their pathological manifestations: visceral leishmaniasis and cutaneous leishmaniasis. Both have the same vectors involved in transmission: the females of two mosquitoes belonging to the genus Phlebotomus perniciosus and P. ariasi.

The most important reservoir demonstrated in our country is the dog (which is also a susceptible host).

Clinical forms of leishmaniasis

Leishmaniasis occurs in three main clinical forms, each with specific characteristics and symptoms:

Cutaneous leishmaniasis:

• This is the most common form of the disease.

• It is characterised by the appearance of skin ulcers, usually painless, which may be single or multiple.
• These lesions may leave permanent scars.

Mucocutaneous leishmaniasis:

• This form affects both the skin and mucous membranes, particularly of the nose, mouth and throat.
• It can cause severe deformities and is difficult to treat.
• Although not as common as cutaneous leishmaniasis, it can be very debilitating.

Visceral leishmaniasis (kala-azar):

• This is the most severe and potentially fatal form of the disease.
• It affects internal organs such as the liver, spleen and bone marrow.
• Symptoms include prolonged fever, weight loss, anaemia, and enlargement of the liver and spleen (hepatosplenomegaly).
• If left untreated, visceral leishmaniasis can be fatal in more than 90% of cases.

Visceral L. visceralis or Kala-azar occurs endemically, being a disease that tends to be chronic and especially affects children. In recent years it has occurred more frequently in people with acquired immunodeficiency syndrome and in people undergoing immunosuppressive treatment (cancer patients, transplant recipients, etc.).

Transmission

Leishmaniasis is transmitted through the bite of infected female phlebotomine sandflies, which feed on blood. The sandflies contract the parasite by biting an infected animal or person, and then transmit the infection to other hosts in their subsequent bites.

In endemic areas, dogs are the main reservoirs of the disease, and transmission to humans occurs mainly in rural or peri-urban areas.

Life cycle of the parasite

The life cycle of Leishmania involves two hosts:

1. Phlebotomine sandflies: the parasite enters the mosquito when it bites an infected host. In the mosquito's gut, the parasite develops into a motile form (promastigote) that migrates into the insect's proboscis, ready to be transmitted at the next bite.
2. Mammals (including humans): When an infected mosquito bites a human or animal, the promastigotes are deposited on the skin. There, the parasites are phagocytosed by macrophages (immune cells), where they are transformed into amastigotes (an intracellular form). The amastigotes multiply within the macrophages and eventually destroy the cells, leading to the symptoms of the disease.

Diagnosis and treatment

• Diagnosis: Diagnosis is made by identification of parasites in samples of affected tissue, such as bone marrow aspirates, skin biopsies or serological tests that detect antibodies to Leishmania.
• Treatment: Treatment depends on the form of the disease. It includes antiparasitic drugs such as pentavalent antimonials, amphotericin B and miltefosine. Cutaneous leishmaniasis can be cured spontaneously in some cases, but mucocutaneous and visceral forms require urgent medical treatment.

In dogs, the incubation period can last for months or years. Signs vary according to the type of leishmaniasis present: cutaneous, mucocutaneous or visceral, and generally include cachexia, alopecia, onychogryposis, lymphadenopathy, hepatomegaly, splenomegaly, etc.

Prevention

• Vector control: Prevention measures include the use of insecticide-treated bed nets, application of repellents and control of the phlebotomine sandfly population.
• Animal protection: Vaccinating and protecting dogs in endemic areas is crucial to reduce transmission of the disease to humans.
• Education and awareness: Informing communities about the risks and preventive measures is essential to control the spread of leishmaniasis.

In summary, leishmaniasis is a serious disease with diverse clinical manifestations that depends on timely diagnosis and appropriate treatment to avoid serious and life-threatening complications.

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