Basic Pathophysiology

The various forms of Leishmaniasis (cutaneous, visceral, mucocutaneous and post-kala-azar dermal) are caused by more than 20 different species of protozoa belonging to the genus Leishmania. Visceral Leishmaniasis is caused by L. donovani, L. infantum and L. chagasi. Some who are infected remain asymptomatic while others progress to serious illness and death, at risk are those who are immunocompromised or malnourished. The promastigote (flagellated) form of the parasite multiplies in the gut of female sand flies after it has ingested the amastigote form from another person (or animal). The promastigotes, which are injected into a human host while the sand fly is feeding, are phagocytised by macrophages where they return to an amastigote form. The amastigotes multiply within the macrophage’s phagolysosomes, protected from an immune response by the host.

The incubation period within a human host can range from 10 days up to 2 years. In visceral leishmaniasis the parasite is able to multiply without suppression from the host’s immune system leading to complications affecting the spleen, liver, intestinal mucosa, bone marrow and lymph nodes. Hematopoiesis is depressed leading to pancytopenia, prothrombin becomes depleted (leading to bleeding complications when combined with thrombocytopenia), and decreased albumin predisposes the patient to edema. The host’s immune system becomes severely compromised as infection spreads and, if left untreated, most patients will die within 2-3 years often from secondary infections such as tuberculosis, pneumonia or dysentery.

Leishmania life cycle:

diagram from: http://www.sciencephoto.com/media/151986/enlarge#

Leishmaniasis: intro and stats

I have chosen to investigate the infectious disease Leishmaniasis, it is a disease that is strongly linked to poverty and as such is relatively unknown in the developed world. Leishmaniasis is a vector-borne parasitic disease caused by over 20 species of the protozoa Leishmania. Leishmaniasis is transmitted through the bite of an infected sand fly. The promasitgote form of the parasite is phagocytized by macrophages where it develops into the amastigote form, multiplies and infects other cells. It is possible for the more severe form of leishmaniasis, visceral leishmaniasis, to be transmitted through transfusions and needle sharing, congenital transmission appears to be very rare.

There are several forms of Leishmaniasis. Cutaneous leishmaniasis is the most common form of the disease; it is rarely fatal and involves skin sores which often resolve on their own without treatment. Mucocutaneous leishmaniasis is a possible complication of cutaneous leishmaniasis, usually due to L. braziliensis, which can cause destruction of mucosal structures such as the nasal septum and soft palate. My focus in this blog will be on the most deadly form of leishmaniasis which is visceral leishmaniasis, also known as kala-azar in parts of the world.

Leishmaniasis is found in 88 countries and as many as 12 million are currently infected. There are 1-2 million new cases each year. Of these 1-2 million new leishmaniasis cases a year and estimated 1.5 million are cutaneous leishmaniasis with the more severe visceral form accounting for about 500,000 new cases. Over 90% of visceral leishmaniasis cases occur in India, Bangladesh, Nepal, Sudan and Brazil. Visceral leishmaniasis is most often caused by L. donovani and L. infantum and without proper treatment it is fatal in >90% of cases. There have been several epidemics of visceral leishmaniasis. Malnutrition, displacement, poor housing and immunosuppresion are known risk factors and thus epidemics tend to occur in hard to reach places that are suffering from famine, war or mass population movements. In Southern Sudan a major epidemic occurring from 1984 to 1994 was estimated to have killed 100,000 in a population of about 300,000 in the upper Nile region. Most cases of leishmaniasis in the United States reflect individuals who were infected during travel or who immigrated to the U.S after they were infected. There have been a few cases of cutaneous leishmaniasis infections in Texas and Oklahoma but there have been no known cases of visceral leishmaniasis acquired in the United States.

There is no prophylactic medication to take if you are traveling to a part of the world where leishmaniasis is endemic. Disease prevention involves avoiding being bitten by the sand fly which hosts the Leishmania genus through use of bug spray, mosquito nets, clothing which covers extremities and avoiding being outside in the evening when the sand fly is most active.

For more information visit: www.cdc.gov

                                                  www.who.org