Background
Leishmaniasis, also known as leishmaniosis, is a disease caused by a group of single celled parasites called Leishmania. These parasites can infect a wide variety of mammals, including: humans, dogs, rodents, and foxes and can cause severe damage to many organs in the body. These parasites are not able to grow in colder climates, this is why Leishmaniasis is mostly limited to subtropical and tropical countries; however, due to the changing climate, it is expected that these parasites will eventually be found in areas that were previously unsusceptible.
Transmission
Leishmania is spread by sandflies, specifically female sandflies because they bite and suck blood. The sandflies bite infected humans or animals, ingesting the parasite in the process. When they bite their next host, they transmit the ingested parasite. In very rare cases, Leishmania can be transmitted from host to host through blood transfusions, infected needles, or vertically from mother to child.
Lifecycle
In sandflies, the parasites exist in a form called promastigotes, which are organisms which have flagella. On inoculation, the host’s immune cells attack and ingest the promastigotes. Inside the host immune cells, the promastigotes shed their flagella to become amastigotes. These amastigotes rapidly replicate within the immune cells, crowding them until the immune cells rupture, spilling out the amastigotes. The spilled amastigotes are quickly consumed by other immune cells, repeating the process. This process allows leishmania to spread locally within tissues or even throughout the entire body if it gets into the bloodstream.
Symptoms
Leishmaniasis can be asymptomatic. The parasites can remain active within the host for years without causing any symptoms, but symptoms may later develop if the host becomes immunocompromised. The symptoms generally depend on which species of Leishmania infects the host, what type of immune response occurs, and how strong the immune response is.
There are three clinical forms of leishmaniasis:
Cutaneous leishmaniasis
This is the mildest form of the disease and also the most common type. People with this form of the disease will have sores on their skin that develop anywhere from a week to months after being bitten by the sandfly. The sores can look like a red papule or can be ulcers that exude pus or dry with a crusted scab. The sores can last for weeks to months. The sores can multiply and grow along the lymphatic vessels. There is prominent scarring after healing of the sores.
Mucocutaneous leishmaniasis
This form is slightly worse than the cutaneous form but it is less common. It can develop on its own or can be a complication of the cutaneous form. This form of leishmaniasis destroys the mucous membranes in the nose, throat, or mouth. This form of the disease can sometimes be fatal. There is permanent damage to the affected mucous membranes.
Visceral Leishmaniasis (Kala Azar)
This is the most severe and dangerous form of leishmaniasis; it is an opportunistic infection in persons with HIV/AIDS or other causes of cell-mediated immunosuppression. Symptoms can develop anywhere from days to years after being bitten by an infected sandfly. It attacks the internal organs of the body, most often the spleen, liver, and bone marrow. People with this form of the disease can display signs and symptoms like:
● Weight loss
● Fever
● Anaemia
● Hepatosplenomegaly
Complications
Kidney failure is a common complication of leishmaniasis, regardless of the type.
Diagnosis
Diagnosis of leishmaniasis can be tricky, as symptoms of the disease can also be suggestive of other pathologies, leading to misdiagnosis.
1. Blood tests can be performed to look for antibodies against the parasites but this isn’t always reliable, because often there are no antibodies despite an active infection.
2. Microscopy can be used to visualize amastigotes in the spleen, liver, or bone marrow but if the amastigotes are present in small amounts, they can be easily missed.
3. Polymerase chain reaction (PCR) looks for the genetic material of the parasites. It is more sensitive than microscopy because it works even if the amastigotes are present in small amounts.
Treatment
There is currently no universally applicable treatment for leishmania. Any treatment must be discussed on an individual case basis. Examples of systemic treatments include liposomal amphotericin or pentavalent antimonial compounds, along with symptomatic treatments, and treatment of co-existing immunocompromise, such as antiretroviral therapy for patients with HIV/AIDS.
Prevention
There are no vaccines or prophylactic medications. Currently, prevention is the best method in addressing leishmaniasis. You can protect against sand flies through using mosquito repellent, appropriate clothing, bed nets, and insect screens. Staying indoors between dusk and dawn is also recommended as this is when sandflies usually attack. It is also important to protect leishmania carriers, such as dogs, with veterinary repellents.
References
R. A. Harvey., Champe, P. C., & Fisher, B. D. (2007). Protoza. In, Lippincottʹs illustrated reviews: Microbiology (2nd ed., pp. 224-225). Philadelphia, USA.: Lippincott Williams & Wilkins.
N. Aronson et al (2017) “Diagnosis and Treatment of Leishmaniasis: Clinical Practice Guidelines by the Infectious Diseases Society of America (IDSA) and the American Society of Tropical Medicine and Hygiene (ASTMH)” Am J Trop Med Hyg. Jan 11; 96(1): 24–4)