Leishmania donovani | |
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Leishmania donovani in bone marrow cell | |
Scientific classification ![]() | |
Domain: | Eukaryota |
Phylum: | Euglenozoa |
Class: | Kinetoplastea |
Order: | Trypanosomatida |
Genus: | Leishmania |
Species: | L. donovani |
Binomial name | |
Leishmania donovani | |
Synonyms | |
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Leishmania donovani is a species of intracellular parasites belonging to the genus Leishmania , a group of haemoflagellate kinetoplastids that cause the disease leishmaniasis. It is a human blood parasite responsible for visceral leishmaniasis or kala-azar, the most severe form of leishmaniasis. It infects the mononuclear phagocyte system including spleen, liver and bone marrow. Infection is transmitted by species of sandfly belonging to the genus Phlebotomus in Old World and Lutzomyia in New World. The species complex it represents is prevalent throughout tropical and temperate regions including Africa (mostly in Sudan), China, India, Nepal, southern Europe, Russia and South America. [2] [3] [4] The species complex is responsible for thousands of deaths every year and has spread to 88 countries, with 350 million people at constant risk of infection and 0.5 million new cases in a year. [5]
L. donovani was independently discovered by two British medical officers William Boog Leishman in Netley, England, and Charles Donovan in Madras, India, in 1903. However, the correct taxonomy was provided by Ronald Ross. The parasite requires two different hosts for a complete life cycle, humans as the definitive host and sandflies as the intermediate host. In some parts of the world other mammals, especially canines, act as reservoir hosts. In human cell they exist as small, spherical and unflagellated amastigote form; while they are elongated with flagellum as promastigote form in sandflies. Unlike other parasitic protists they are unable to directly penetrate the host cell, and are dependent upon phagocytosis. [6] [7] The whole genome sequence of L. donovani obtained from southeastern Nepal was published in 2011. [8]
L. donovani sensu stricto is in a species complex with the closely related L. infantum , which causes the same disease. The former is commonly found in East Africa and the Indian subcontinent, while the latter is found in Europe, North Africa, and Latin America. The split is done in 2007, and references to L. donovani often still refer to the entire complex (sensu lato). [1] As of 2022, the parasite causes 50,000 to 90,000 infections worldwide. [9]
One of the earliest known epidemics of L. donovani infection (kala-azar as it was called in Hindi) was known in India just after the Indian Rebellion of 1857. The first medical record was however only in 1870 by British medical officers from Assam. In 1900, an English soldier stationed at Dum Dum, West Bengal, died at the Army Medical School in Netley, England. The autopsy was performed by William Boog Leishman. He processed the tissue sample of the enlarged spleen using a staining technique (now known as Leishman's stain) which he had just developed, and discovered the protozoan parasites using microscopy. But he mistakenly considered the parasites to be degenerate trypanosomes, already known protozoan parasites in Africa and South America. [10] In 1903, Leishman published his discovery as "On the possibility of the occurrence of trypanosomiasis in India" in the British Medical Journal , which appeared on 11 May. [11]
Another British medical officer Charles Donovan, who was serving in the Indian Medical Service, had found the parasites in April of that year at the Government General Hospital in Madras. After reading Leishman paper, Donovan confirmed on 17 June that the parasites (by then known as "Leishman bodies") were definitely the causative agents of kala-azar. [12] [13] He wrote a commentary of his discovery in relation to that of Leishman in the same journal using the same title as that of Leishman's, that appeared on 11 July 1903. [14]
Soon a controversy arose as to whom such a monumental discovery should be credited. Donovan sent some of his slides to Ronald Ross, who was at the time in Liverpool, and to Alphonse Laveran at the Pasteur Institute in Paris. Laveran and his colleague Félix Mesnil identified the protozoan (and yet wrongly) to be members of Piroplasmida, and gave the scientific name Piroplasma donovanii. It was Ross who resolved the conflict of priority in the discovery and correctly identified the species as member of the novel genus Leishmania. He gave the popular name "Leishman-Donovan bodies", and subsequently the valid binomial Leishmania donovani, thereby equally crediting the two rivals. [10] [15] [16]
Leishmania donovani is a unicellular eukaryote having a well-defined nucleus and other cell organelles including a kinetoplast and a flagellum. This species has n=36 chromosomes. [17] Depending on its host it exists in two structural variants, as follows: [16] [18] [19] [20]
Leishmania donovani is a digenetic parasite passing its life cycle in two different hosts.
In humans the metacyclic promastigotes are injected by sandfly through the skin during its blood meal. When sandfly bites using its proboscis it ejects the parasites that are stored inside the hollow tube. Some promastigotes may enter the blood stream directly where some are destroyed by macrophagic cytolysis. But many are also taken up through phagocytosis by mononuclear phagocytes in liver, spleen and bone marrow. [21] Inside the cells they undergo spontaneous transformation into oval-shaped amastigotes. [22] [23]
Granulocytes selectively kill the promastigotes by oxidative mechanism, while amastigotes are resistant. [24] Then the surviving amastigotes undergo cell division using simple binary fission. Multiplication continues until the host cell can no longer hold and ruptures. In a fully congested cell there can be as many as 50 to 200 amastigotes, which are released into tissue cavities. Each individual amastigote is then capable of invading fresh cells. As a result, the entire tissue is progressively infected and destroyed. A number of free amastigotes then enters the blood stream where many are phagocytosed by macrophages. These free and phagocytosed amastigotes in peripheral blood are then sucked up by blood-feeding sandfly. [25] [26] [27]
L. donovani undergo further development only in the digestive tract of the female sandfly. Hence only females are responsible for transmitting the infection. Once the amastigotes are ingested, they enter the midgut of the sandfly. Then they undergo structural modification into flagellated promastigotes, becoming larger and considerably elongated. They get attached to the gut epithelial lining where they multiply rapidly by binary fission. (They are also capable of sexual reproduction by genetic hybridisation in the sandfly gut.) [28] They then migrate back towards the anterior part of the digestive system such as pharynx and buccal cavity. This process is known as anterior station development, which is unique in Leishmania. A heavy infection of pharynx can be observed within 6 to 9 days after initial blood meal. The promastigotes become infective only by this time, and the event is called the metacyclic stage. [16] [29] The metacyclic promastigotes then enter the hollow proboscis where they accumulate and completely block the food passage. Immediately upon biting a human, the parasites are released, which invariably results in infection. [26]
The stages of development in sandfly can be described as follows: [18]
Dogs are known to be susceptible to L. donovani infection. [33] Especially in the New World, infection is a zoonotic disease, involving different canine species, including domestic dog and the two fox species, Lycalopex vetulus and Cerdocyon thous . In the Mediterranean region domestic dogs and the three fox species Vulpes vulpes , V. corsac and V. zerda are common reservoir hosts. [34] [35] In Africa and Brazil, some marsupials and rodents are also reported to harbour L. donovani. [36]
It is estimated that visceral leishmaniasis (VL) affects more than 100 million people worldwide, [37] with 1.5 to 2 million new cases and more than 70,000 deaths each year. [38] As of the 2022 report, there were 50,000 to 90,000 infections worldwide in 2020, and the World Health Organization estimates that only between 25 and 45% of the cases were reported. [9] Although L. donovani is only the second-most prevalent Leishmania causing VL, it is the most dangerous form and directly fatal to humans. Over 90% of reported cases are from India, Bangladesh, Nepal, Sudan and Brazil. [39] In India, it is prevalent in the eastern region including Bihar, West Bengal, eastern Uttar Pradesh, Assam and foothills of Sikkim. [40] It is responsible for tens of thousands of mortality among Africans in eastern and southern parts of Sudan. During the epidemic of 1984–1994 death toll was as high as 70% in the Sudanese population. [41] Moreover, due to emergence of drug resistance the prevalence is not subsiding, and in fact has spread to central Europe. For example, during the late 1990s hundreds of cases were reported in Switzerland. [42]
L. donovani is the causative agent of visceral leishmaniasis, traditionally known as kala-azar ("black fever", particularly in India), because of its characteristic symptoms. The disease is highly lethal if not treated properly. The incubation period generally ranges from 3 to 6 months, and in some cases may be over a year. In Indian leishmaniasis, incubation can be as short as 10 days. The target cells are those of mononuclear phagocyte system. The two main tissues of infection are spleen and liver. [43]
Clinical symptoms include pyrexia (recurring high fever which may be continuous or remittent), enlargement of spleen and liver, and heavy skin pigmentation which darkens the physical appearance (the reason for naming "black fever"). To a lesser extent, mucosa of the small intestine and lymph nodes are also invaded by the parasite. Morphological symptoms are noticeable particularly on facial and abdominal regions. Skin becomes coarse and hard. In African infections, warty eruptions are common. In a fully developed stage, the patient shows emaciation and anaemia. Where medical facilities are poor, mortality can be as high as 75–95% within 2 years of epidemics. The disease is often accompanied by complications with dysentery, tuberculosis, septicaemia and even HIV infection. [26] [44] [45]
Amastigotes of L. donovani enter macrophages via a Rac1- and Arf6-dependent process, and are found in phagocytic vacuoles that interact with endosomes and lysosomes and acquire lysosomal features. [46] During phagocytosis by macrophages, the promastigotes inhibit the formation of the phagolysosome, a cellular product by which invading pathogens are removed. The promastigote can do this using its glycolipid lipophosphoglycan (LPG) on its cell membrane. LPG causes disorganisation of F-actin and disruption of phagosomal lipid microdomains. [47] They are capable of evading the microbicidal actions of macrophages, which can kill ordinary pathogens using reactive nitrogen and oxygen intermediates. They effectively subvert the production of reactive oxygen species. In this way the amastigotes are able to survive and replicate inside these primary immune systems. The parasites manipulate the cell signalling pathway of the macrophages, such as down-regulating of Jak/stat signalling, NO and TNF-α production, and also by blocking the NF-κB-dependent pathway. [48] There are two major mechanisms of immune evasion such as induction of immune suppressive IL-10 responses and the generation of poor and functionally impaired CD8(+) T-cell responses. [49]
The conventional treatment method is an intravenous injection with antimony compounds, such as pentostam.[ citation needed ] Unfortunately, these chemotherapeutics are so poisonous that about 15% of the patients die from the treatments.[ citation needed ] To compound the situation, drug resistance has evolved in the parasites against the traditional antimonials. According to rough estimates, about 40% of patients in India are already resistant to this therapy. [42]
Another antimicrobial drug amphotericin B is also commonly used. Liposomal amphotericin B (L-AmB) has been a drug of choice in India, but is practically useless in Africa because of low effectiveness in the African strain of the parasite. [50] Further, amphotericin B has severe adverse effects. Its acute effects includes nausea, vomiting, rigors, fever, hypertension or hypotension, and hypoxia, and its chronic effect is nephrotoxicity. [51]
In 1999, an anticancer drug miltefosine was demonstrated to be highly effective (95% cure rate) among Indian patients. [52] This was the first time an oral drug is effective for visceral leishmaniasis. Clinical trials showed that the new drug is relatively harmless. The most adverse effects were only vomiting and diarrhoea in 20–28% patients, which were rather mild. The drug has been officially approved in India. The recommended dosage is 100 mg per day over a period of four weeks. [53] [54]
L. donovani is now considered to be a species complex as indicated by different pathological symptoms occurring in different geographical areas where the species of the vector sandfly are also different. However, none of the parasites are morphologically distinguishable, except by molecular analysis, making them cryptic species. Molecular data show that genotype is strongly correlated with geographical origin. [55] DNA sequencing of different geographical strains indicates that the protozoan complex can be classified into two valid taxa, L. donovani and L. infantum . The genus Leishmania most likely originated in South America, from where it migrated to Asia. L. donovani and L. infantum diverged ~1 Mya, with further divergence of infraspecific genetic groups between 0.4 and 0.8 Mya. [1]
Leishmania is a parasitic protozoan, a single-celled organism of the genus Leishmania that is responsible for the disease leishmaniasis. They are spread by sandflies of the genus Phlebotomus in the Old World, and of the genus Lutzomyia in the New World. At least 93 sandfly species are proven or probable vectors worldwide. Their primary hosts are vertebrates; Leishmania commonly infects hyraxes, canids, rodents, and humans.
Trypanosomatida is a group of kinetoplastid unicellular organisms distinguished by having only a single flagellum. The name is derived from the Greek trypano (borer) and soma (body) because of the corkscrew-like motion of some trypanosomatid species. All members are exclusively parasitic, found primarily in insects. A few genera have life-cycles involving a secondary host, which may be a vertebrate, invertebrate or plant. These include several species that cause major diseases in humans. Some trypanosomatida are intracellular parasites, with the important exception of Trypanosoma brucei.
Leishmaniasis is a wide array of clinical manifestations caused by protozoal parasites of the Trypanosomatida genus Leishmania. It is generally spread through the bite of phlebotomine sandflies, Phlebotomus and Lutzomyia, and occurs most frequently in the tropics and sub-tropics of Africa, Asia, the Americas, and southern Europe. The disease can present in three main ways: cutaneous, mucocutaneous, or visceral. The cutaneous form presents with skin ulcers, while the mucocutaneous form presents with ulcers of the skin, mouth, and nose. The visceral form starts with skin ulcers and later presents with fever, low red blood cell count, and enlarged spleen and liver.
Charles Louis Alphonse Laveran was a French physician who won the Nobel Prize in Physiology or Medicine in 1907 for his discoveries of parasitic protozoans as causative agents of infectious diseases such as malaria and trypanosomiasis. Following his father, Louis Théodore Laveran, he took up military medicine as his profession. He obtained his medical degree from University of Strasbourg in 1867.
Sandfly or sand fly is a colloquial name for any species or genus of flying, biting, blood-sucking dipteran (fly) encountered in sandy areas. In the United States, sandfly may refer to certain horse flies that are also known as "greenheads", or to members of the family Ceratopogonidae. The bites usually result in a small, intensely itchy bump or welt, the strength of which intensifies over a period of 5-7 days before dissipating. Moderate relief is achieved with varying success through the application of over the counter products such as Benadryl (ingested) or an analgesic cream such as After Bite. Outside the United States, sandfly may refer to members of the subfamily Phlebotominae within the Psychodidae. Biting midges (Ceratopogonidae) are sometimes called sandflies or no-see-ums. New Zealand sandflies are in the genus of sand fly Austrosimulium, a type of black fly.
Lutzomyia is a genus of phlebotomine sand flies consisting of nearly 400 species, at least 33 of which have medical importance as vectors of human disease. Species of the genus Lutzomyia are found only in the New World, distributed in southern areas of the Nearctic and throughout the Neotropical realm. Lutzomyia is one of the two genera of the subfamily Phlebotominae to transmit the Leishmania parasite, with the other being Phlebotomus, found only in the Old World. Lutzomyia sand flies also serve as vectors for the bacterial Carrion's disease and a number of arboviruses.
Cutaneous leishmaniasis is the most common form of leishmaniasis affecting humans. It is a skin infection caused by a single-celled parasite that is transmitted by the bite of a phlebotomine sand fly. There are about thirty species of Leishmania that may cause cutaneous leishmaniasis.
Visceral leishmaniasis (VL), also known as kala-azar or "black fever", is the most severe form of leishmaniasis and, without proper diagnosis and treatment, is associated with high fatality. Leishmaniasis is a disease caused by protozoan parasites of the genus Leishmania.
Miltefosine, sold under the trade name Impavido among others, is a medication mainly used to treat leishmaniasis and free-living amoeba infections such as Naegleria fowleri and Balamuthia mandrillaris. This includes the three forms of leishmaniasis: cutaneous, visceral and mucosal. It may be used with liposomal amphotericin B or paromomycin. It is taken by mouth.
Leishmania infantum is the causative agent of infantile visceral leishmaniasis in the Mediterranean region and in Latin America, where it has been called Leishmania chagasi. It is also an unusual cause of cutaneous leishmaniasis, which is normally caused by specific lineages. Wild canids and domestic dogs are the natural reservoir of this organism. The sandfly species Lutzomyia longipalpis serves as the primary vector for the transmission of the disease.
Leishmania major is a species of parasite found in the genus Leishmania, and is associated with the disease zoonotic cutaneous leishmaniasis. L. major is an intracellular pathogen which infects the macrophages and dendritic cells of the immune system. Though Leishmania species are found on every continent aside from Antarctica, Leishmania major is found only in the Eastern Hemisphere, specifically in Northern Africa, the Middle East, Northwestern China, and Northwestern India.
Canine leishmaniasis (LEESH-ma-NIGH-ah-sis) is a zoonotic disease caused by Leishmania parasites transmitted by the bite of an infected phlebotomine sandfly. There have been no documented cases of leishmaniasis transmission from dogs to humans. Canine leishmaniasis was first identified in Europe in 1903, and in 1940, 40% of all dogs in Rome were determined to be positive for leishmaniasis. Traditionally thought of as a disease only found near the Mediterranean basin, 2008 research claims new findings are evidence that canine leishmaniasis is currently expanding in continental climate areas of northwestern Italy, far from the recognized disease-endemic areas along the Mediterranean coasts. Cases of leishmaniasis began appearing in North America in 2000, and, as of 2008, Leishmania-positive foxhounds have been reported in 22 U.S. states and two Canadian provinces.
Leishmania tropica is a flagellate parasite and the cause of anthroponotic cutaneous leishmaniasis in humans. This parasite is restricted to Afro-Eurasia and is a common cause of infection in Afghanistan, Iran, Syria, Yemen, Algeria, Morocco, and northern India.
Leishmania braziliensis is a Leishmania species found in South America. It is associated with leishmaniasis.
Leishmania mexicana is a species of obligate intracellular parasites of the protozoan genus Leishmania. In Mexico and Central America, this parasite is the primary cause of cutaneous leishmaniasis.
Post-kala-azar dermal leishmaniasis (PKDL) is a complication of visceral leishmaniasis (VL); it is characterised by a macular, maculopapular, and nodular rash in a patient who has recovered from VL and who is otherwise well. The rash usually starts around the mouth from where it spreads to other parts of the body depending on severity.
Jenefer Blackwell is a Professor of Molecular Parasitology at the Telethon Kids Institute in the University of Western Australia. She studies host susceptibility and resistance to infectious diseases.
Lutzomyia longipalpis is a species complex of sandfly belonging to the family Psychodidae. This species is primarily present in Central and South America, but has also appeared in Mexico. There have been reports of L. longipalpis as far south as Argentina, as they are found in a wide variety of ecological conditions. Both males and females feed on sugars from plants and aphids, but only adult females feed on the blood of other mammals. The species has recently begun appearing in urban areas throughout Brazil, and serves as a key vessel for the propagation of the parasite Leishmania infantum. The presence of these flies appears to be strongly correlated to the presence of domestic chickens in Latin America. The first major urban outbreak of the lethal Visceral leishmanias epidemic was detected in Teresina, Piauí State in the early 1980s following a massive planting of acacias.
Kala azar in India refers to the special circumstances of the disease kala azar as it exists in India. Kala azar is a major health problem in India with an estimated 146,700 new cases per year as of 2012. In the disease a parasite causes sickness after migrating to internal organs such as the liver, spleen and bone marrow. If left untreated the disease almost always results in the death. Signs and symptoms include fever, weight loss, fatigue, anemia, and substantial swelling of the liver and spleen.
María Dora Feliciangeli was Professor of Medical Entomology at the University of Carabobo, Venezuela, who worked on the transmission of tropical parasites especially American trypanosomiasis and leishmaniasis. She was Coordinator of the National Reference Center of Sandflies and the Medical Entomology Section.
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