New Review Digs Deep Into Rapid Diagnostic Tests for Visceral Leishmaniasis

What Is Leishmaniasis?

 Leishmaniasis is a type of infection which is caused by protozoal parasites from the Leishmania species. These parasites are spread from person to person through the bite of the female phlebotomine sand fly. This sandfly reside in many tropical and temperate countries.

There are two clinical syndrome of leishmaniasis: visceral or cutaneous. Visceral leishmaniasis (VL)is a type of leishmaniasis that affects the organs of the body. Cutaneous leishmaniasis (CL) on the other hand is the most common form of leishmaniasis; this type infects the skin. A type of cutaneous leishmaniasis is mucocutaneous leishmaniasis (ML) which invades the mucocutaneous membranes.

Leishmania protozoal parasites are microscopic parasites; there are about 21 species of them which affects humans, including the L. donovani complex and the L. Mexicana complex. This parasite is transmitted from person to person by the sandfly. When the sandfly carrier bites a person, it injects small numbers of parasites which are rapidly taken up by mononuclear blood cells. This stage is called the promastigote stage. The parasites then enter the mononuclear cells and enter the amastigote stage and begin to multiply and infect other cells and tissues. These parasites are then taken up by sandflies again; they may also get the parasite from infected animals such as dogs, foxes, or rodents. A less common route of transmission is through blood transfusion or through drug users sharing contaminated needles. Leishmania may also be transmitted from a pregnant mother to her fetus.

There are some people who are at high risk of acquiring the parasites. People who are exposed to infected sandflies are those who can readily become infected with Leishmania. These sandflies are most active after dusk in rural areas. Travelers who go in these places are susceptible to this infection. Examples of these travellers are adventure travelers, Peace Corps workers, missionaries, soldiers, and those with occupational activities that require them to live in rural areas. The immune response towards the parasite is determined by genes. In visceral leishmaniasis, a weak immune response is associated with more severe disease. Those who have weak immune responses include those who are malnourished and those who are infected with the human immunodeficiency virus (HIV). However, in mucocutaneous leishmaniasis, the symptoms appear to be caused in part by an overactive immune response. The inflammatory response is overstimulated, making the parasite more dangerous.

In some people Leishmania may hide in the body for years and slowly begin to multiply if the immune system is suppressed, as what happens in those who have received chemotherapy, use steroids, or are infected with HIV. Leishmania infection may bring about signs and symptoms such as weight loss, low blood counts (pancytopenia), enlargement of the liver and spleen (hepatosplenomegaly), intermittent fever and high levels of immune globulin in the blood (hypergammaglobulinemia). There may be darkness of the skin, a condition known as “kala-zar,” which means “black sickness.” There may be a persistent rash or pigment changes in the skin. The disease may affect the kidneys, the bowels and the lungs, further causing problems. Cutaneous leishmaniasis (CL) can bring about skin sores which may persist for several weeks.

Rapid Diagnostic Tests for Visceral Leishmaniasis

A recent review done by researchers from the Cochrane Infectious Disease Group, co-ordinated through the editorial base in LSTM, conducted an independent review into the effectiveness of rapid diagnostic tests in diagnosing patients with visceral leishmaniasis (VL). The findings were published in The Cochrane Library. The researchers found 24 studies which contained information about five different RDTs, with a total of 4271 participants. An RDT, the rK39 immunochromatographic test gave correct, positive results in 92% of the people with VL and it gave correct, negative results in 92% of the people who did not have the disease. A second RDT, the latex agglutination test gave correct, positive results in 64% of the people with the disease and it gave correct, negative results in 93% of the people without the disease. For the other RDTs evaluated, there are too few studies to assess their accuracy.

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