Kala Azar Vector

[Ara Kistner]

Theleishmaniases are a group of diseases caused by protozoan parasites from more than 20 Leishmania species. These parasites are transmitted to humans by the bite of an infected female phlebotomine sandfly, a tiny 2-3 mm long insect\r\n vector. There are three main forms of the disease: cutaneous leishmaniasis (CL), visceral leishmaniasis (VL), also known as kala-azar, and mucocutaneous leishmaniasis (MCL). CL is the most common form, VL is the most severe form and MCL is the most\r\n disabling form of the disease.

Today, more than 1 billion people live in areas endemic for leishmaniasis and are at risk of infection. Globally, an estimated 30 000 new cases of VL and more than 1 million new cases of CL occur annually.

Much progress has occurred in the country in the past decades. Kala-azar cases have decreased by 98% (1 275 cases in 2021) since the start of intensified activities in 1992 (77 102 cases). To get to the 2030 Sustainable Development Goals and WHO targets\r\n for kala-azar elimination as a public health problem, block level incidence of cases should be reduced to less than 1 case per 10 000 population. This target aligned with the new NTDs roadmap 2021-2030 (URL: ). By the end of 2021, 98% of blocks have achieved the WHO elimination threshold \r\n and only seven blocks which are yet to reach the targets. WHO is supporting the national programme in intensifying activities to help achieve targets and ensure sustainability of kala-azar elimination.

A complication of kala-azar, is mainly seen in East Africa and South-East Asia, including India. It is characterized by discoloured (hypopigmented) flat skin (macular) rash, combined with some slightly elevated (maculopapular) or elevated (nodular) rash,\r\n usually in patients who have recovered from the disease. Post-kala-azar dermal leishmaniasis (PKDL) usually appears six months to one or more years after apparent cure of kala-azar, but it may occur earlier or even concurrently with kala-azar. PKDL\r\n heals spontaneously in most cases in Africa but rarely in patients in India.

Kala-azar-HIV coinfected people have high chance of developing the full-blown clinical disease, and high relapse and mortality rates. Antiretroviral treatment reduces the development of the disease, delays relapses and increases the survival of the coinfected\r\n patients. As of 2021, leishmania-HIV coinfection has been reported from 45 countries. High Leishmania-HIV coinfection rates are reported from Brazil, Ethiopia and the state of Bihar in India.

Kala-azar is characterized by irregular bouts of fever, substantial weight loss, swelling of the spleen and liver and severe anaemia. If the disease is not treated early and in time, affected individuals can die within two years.

In Kala-azar, diagnosis is made by combining clinical signs with parasitological, or serological tests (such as rapid diagnostic tests). In cutaneous and mucocutaneous leishmaniasis serological tests have limited value and clinical manifestation\r\n with parasitological tests confirms the diagnosis. Anti-kala-azar treatment depends on the causative species and the condition of the patient (e.g. pregnancy, immunosuppression). Regardless of the causative Leishmania species, antileishmanial\r\n treatment cannot provide a complete cure. The parasite remains in the human body and can cause a relapse when there is immunosuppression.

The leishmaniases are a group of diseases caused by protozoan parasites from more than 20 Leishmania species. These parasites are transmitted to humans by the bite of an infected female phlebotomine sandfly, a tiny 2-3 mm long insect vector. There are three main forms of the disease: cutaneous leishmaniasis (CL), visceral leishmaniasis (VL), also known as kala-azar, and mucocutaneous leishmaniasis (MCL). CL is the most common form, VL is the most severe form and MCL is the most disabling form of the disease.

Much progress has occurred in the country in the past decades. Kala-azar cases have decreased by 98% (1 275 cases in 2021) since the start of intensified activities in 1992 (77 102 cases). To get to the 2030 Sustainable Development Goals and WHO targets for kala-azar elimination as a public health problem, block level incidence of cases should be reduced to less than 1 case per 10 000 population. This target aligned with the new NTDs roadmap 2021-2030 (URL: ). By the end of 2021, 98% of blocks have achieved the WHO elimination threshold and only seven blocks which are yet to reach the targets. WHO is supporting the national programme in intensifying activities to help achieve targets and ensure sustainability of kala-azar elimination.

A complication of kala-azar, is mainly seen in East Africa and South-East Asia, including India. It is characterized by discoloured (hypopigmented) flat skin (macular) rash, combined with some slightly elevated (maculopapular) or elevated (nodular) rash, usually in patients who have recovered from the disease. Post-kala-azar dermal leishmaniasis (PKDL) usually appears six months to one or more years after apparent cure of kala-azar, but it may occur earlier or even concurrently with kala-azar. PKDL heals spontaneously in most cases in Africa but rarely in patients in India.

Kala-azar-HIV coinfected people have high chance of developing the full-blown clinical disease, and high relapse and mortality rates. Antiretroviral treatment reduces the development of the disease, delays relapses and increases the survival of the coinfected patients. As of 2021, leishmania-HIV coinfection has been reported from 45 countries. High Leishmania-HIV coinfection rates are reported from Brazil, Ethiopia and the state of Bihar in India.

In Kala-azar, diagnosis is made by combining clinical signs with parasitological, or serological tests (such as rapid diagnostic tests). In cutaneous and mucocutaneous leishmaniasis serological tests have limited value and clinical manifestation with parasitological tests confirms the diagnosis. Anti-kala-azar treatment depends on the causative species and the condition of the patient (e.g. pregnancy, immunosuppression). Regardless of the causative Leishmania species, antileishmanial treatment cannot provide a complete cure. The parasite remains in the human body and can cause a relapse when there is immunosuppression.

Leishmaniasis is a vector-borne disease that is transmitted by sandflies and caused by obligate intracellular protozoa of the genus Leishmania. Human infection is caused by about 21 of 30 species that infect mammals. These include the L. donovani complex with 3 species (L. donovani, L. infantum, and L. chagasi); the L. mexicana complex with 3 main species (L. mexicana, L. amazonensis, and L. venezuelensis); L. tropica; L. major; L. aethiopica; and the subgenus Viannia with 4 main species (L. (V.) braziliensis, L. (V.) guyanensis, L. (V.) panamensis, and L. (V.) peruviana). The different species are morphologically indistinguishable, but they can be differentiated by isoenzyme analysis, molecular methods, or monoclonal antibodies.

Leishmaniasis is transmitted by the bite of infected female phlebotomine sandflies. The sandflies inject the infective stage (i.e., promastigotes) from their proboscis during blood meals . Promastigotes that reach the puncture wound are phagocytized by macrophages and other types of mononuclear phagocytic cells. Promastigotes transform in these cells into the tissue stage of the parasite (i.e., amastigotes) , which multiply by simple division and proceed to infect other mononuclear phagocytic cells . Parasite, host, and other factors affect whether the infection becomes symptomatic and whether cutaneous or visceral leishmaniasis results. Sandflies become infected by ingesting infected cells during blood meals (, ). In sandflies, amastigotes transform into promastigotes, develop in the gut (in the hindgut for leishmanial organisms in the Viannia subgenus; in the midgut for organisms in the Leishmania subgenus), and migrate to the proboscis .

Human Leishmaniasis encompasses multiple clinical syndromes, most notably visceral, cutaneous, and mucosal forms. Infections can result in two main forms of disease, cutaneous leishmaniasis and visceral leishmaniasis (kala-azar). Different species can be associated with diverse clinical manifestations and sequelae. Species identification can facilitate clinical management, such as decisions regarding whether/which treatment is indicated. species, geographic location, and immune response of the host. Cutaneous leishmaniasis is characterized by one or more cutaneous lesions on areas where sandflies have fed. Persons who have cutaneous leishmaniasis have one or more sores on their skin. The sores can change in size and appearance over time. They often end up looking somewhat like a volcano, with a raised edge and central crater. A scab covers some sores. The sores can be painless or painful. Some people have swollen glands near the sores (for example, in the armpit if the sores are on the arm or hand).

Persons who have visceral leishmaniasis usually have fever, weight loss, and an enlarged spleen and liver (usually the spleen is bigger than the liver). Some patients have swollen glands. Certain blood tests are abnormal. For example, patients usually have low blood counts, including a low red blood cell count (anemia), low white blood cell count, and low platelet count. Some patients develop post kala-azar dermal leishmaniasis. Visceral leishmaniasis is becoming an important opportunistic infection in areas where it coexists with HIV.

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