Trypanosomosis
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Trypanosomiasis or trypanosomosis is the name of several diseases in
vertebrates Vertebrates () are animals with a vertebral column (backbone or spine), and a cranium, or skull. The vertebral column surrounds and protects the spinal cord, while the cranium protects the brain. The vertebrates make up the subphylum Vertebra ...
caused by
parasitic Parasitism is a close relationship between species, where one organism, the parasite, lives (at least some of the time) on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The ent ...
protozoa Protozoa (: protozoan or protozoon; alternative plural: protozoans) are a polyphyletic group of single-celled eukaryotes, either free-living or parasitic, that feed on organic matter such as other microorganisms or organic debris. Historically ...
n trypanosomes of the genus ''
Trypanosoma ''Trypanosoma'' is a genus of kinetoplastids (class Trypanosomatidae), a monophyletic group of unicellular parasitic flagellate protozoa. Trypanosoma is part of the phylum Euglenozoa. The name is derived from the Ancient Greek ''trypano-'' (b ...
''. In humans this includes
African trypanosomiasis African trypanosomiasis is an insect-borne parasitic infection of humans and other animals. Human African trypanosomiasis (HAT), also known as African sleeping sickness or simply sleeping sickness, is caused by the species ''Trypanosoma bru ...
and
Chagas disease Chagas disease, also known as American trypanosomiasis, is a tropical parasitic disease caused by ''Trypanosoma cruzi''. It is spread mostly by insects in the subfamily Triatominae, known as "kissing bugs". The symptoms change throughout the ...
. A number of other diseases occur in other animals. Human African trypanosomiasis, which is caused by either ''
Trypanosoma brucei gambiense ''Trypanosoma brucei'' is a species of parasitic kinetoplastid belonging to the genus ''Trypanosoma'' that is present in sub-Saharan Africa. Unlike other protozoan parasites that normally infect blood and tissue cells, it is exclusively extrace ...
'' or ''Trypanosoma brucei rhodesiense'', is presently estimated to threaten over 40 million people in
sub-Saharan Africa Sub-Saharan Africa is the area and regions of the continent of Africa that lie south of the Sahara. These include Central Africa, East Africa, Southern Africa, and West Africa. Geopolitically, in addition to the list of sovereign states and ...
, especially in rural areas and populations affected by war or poverty. However, only 1.5 million people are estimated to live in areas at moderate or high risk, and for over 20 years the number of cases has been going down due to systematic surveillance and control efforts: in 1998 almost 40,000 cases were reported but almost 300,000 cases were suspected to have occurred; in 2009, the number dropped below 10,000; and in 2018 it dropped below 1000, and it has remained under that number ever since. Chagas disease causes 21,000 deaths per year mainly in
Latin America Latin America is the cultural region of the Americas where Romance languages are predominantly spoken, primarily Spanish language, Spanish and Portuguese language, Portuguese. Latin America is defined according to cultural identity, not geogr ...
.


Signs and symptoms

The
tsetse fly Tsetse ( , or ) (sometimes spelled tzetze; also known as tik-tik flies) are large, biting flies that inhabit much of tropical Africa. Tsetse flies include all the species in the genus ''Glossina'', which are placed in their own family, Gloss ...
bite erupts into a red chancre sore and within a few weeks, the person can experience fever, swollen lymph glands, blood in urine, aching muscles and joints, headaches and irritability. In the first phase, the patient has only intermittent bouts of fever with lymphadenopathy together with other non-specific signs and symptoms. The second stage of the disease is marked by involvement of the central nervous system with extensive neurological effects like changes in personality, alteration of the biological clock (the circadian rhythm), confusion, slurred speech, seizures and difficulty in walking and talking. These problems can develop over many years and if not treated, the person dies. It is common in Subsaharan Africa.


Diagnosis

Cattle may show enlarged lymph nodes and internal organs. Haemolytic
anaemia Anemia (also spelt anaemia in British English) is a blood disorder in which the blood has a reduced ability to carry oxygen. This can be due to a lower than normal number of red blood cells, a reduction in the amount of hemoglobin availab ...
is a characteristic sign. Systemic disease and reproductive wastage are common, and cattle appear to waste away. Horses with dourine show signs of ventral and genital edema and urticaria. Infected dogs and cats may show severe systemic signs. Diagnosis relies on recognition of the
flagellate A flagellate is a cell or organism with one or more whip-like appendages called flagella. The word ''flagellate'' also describes a particular construction (or level of organization) characteristic of many prokaryotes and eukaryotes and the ...
on a
blood smear A blood smear, peripheral blood smear or blood film is a thin layer of blood smeared on a glass microscope slide and then stained in such a way as to allow the various blood cells to be examined microscopically. Blood smears are examined in the i ...
. Motile organisms may be visible in the
buffy coat The buffy coat is the fraction of an anticoagulated blood sample that contains most of the leukocytes and thrombocytes following centrifugation. Description After centrifugation, one can distinguish a layer of clear fluid (the plasma), a laye ...
when a blood sample is spun down. Serological testing is also common. One common way in which trypanosomiasis can be diagnosed in humans is through the detection of antibodies against trypanosomes made by host organisms. One commonly used antibody test which operated based on this principle is the card agglutination test, C.A.T.T. for T. gambiense. In this test, reagent is mixed with blood and shaken. Within a matter of minutes, a researcher or public health professional can determine whether someone has made these antibodies and therefore is infected with trypanosomes. Regarding the accuracy of this test, it is reported to have an 87 to 98 percent sensitivity rating. Another way to diagnose trypanosomiasis in humans is to detect the trypanosome protozoans themselves. One way to do this would be to use lymph node aspirate. In this test, which has a sensitivity of between 40 and 80 percent, a healthcare worker will first find a cervical lymph node which is enlarged. Once the healthcare worker has punctured that lymph node, its aspirate is examined under a microscope for trypanosomes to confirm diagnosis.


Prevention

The use of trypanotolerant breeds for livestock farming should be considered if the disease is widespread. Fly control is another option but is difficult to implement. The main approaches to controlling African trypanosomiasis are to reduce the reservoirs of infection and the presence of the tsetse fly. Screening of people at risk helps identify patients at an early stage. Diagnosis should be made as early as possible and before the advanced stage to avoid complicated, difficult and risky treatment procedures.


Treatment

Stage I of the condition is usually treated with
pentamidine Pentamidine is an antimicrobial medication used to treat African trypanosomiasis, leishmaniasis, '' Balamuthia'' infections, babesiosis, and to prevent and treat pneumocystis pneumonia (PCP) in people with poor immune function. In African trypa ...
or
suramin Suramin is a medication used to treat African sleeping sickness and river blindness. It is the treatment of choice for sleeping sickness without central nervous system involvement. It is given by injection into a vein. Suramin causes a fai ...
through intramuscular injection or intravenous infusion if sufficient observation is possible. Stage II of the disease is typically treated with
melarsoprol Melarsoprol is an arsenic-containing medication used for the treatment of sleeping sickness (African trypanosomiasis). It is specifically used for second-stage disease caused by '' Trypanosoma brucei rhodesiense'' when the central nervous system ...
or
eflornithine Eflornithine, sold under the brand name Vaniqa among others, is a medication used to treat African trypanosomiasis (sleeping sickness) and excessive hair growth on the face in women. Specifically it is used for the second stage of sleeping sic ...
preferably introduced to the body intravenously. Both pentamidine and suramin have limited side effects. Melarsoprol is extremely effective but has many serious side effects which can cause neurological damage to a patient, however, the drug is often a patient's last hope in many late stage cases. Eflornithine is extremely expensive but has side effects that may be treated with ease. In regions of the world where the disease is common eflornithine is provided for free by the World Health Organization.


Epidemiology

Trypanosomes and trypanosomiasis disease is transmitted through the
tsetse fly Tsetse ( , or ) (sometimes spelled tzetze; also known as tik-tik flies) are large, biting flies that inhabit much of tropical Africa. Tsetse flies include all the species in the genus ''Glossina'', which are placed in their own family, Gloss ...
. As many as 90 percent of sleeping sickness cases are caused by the
Glossina Tsetse ( , or ) (sometimes spelled tzetze; also known as tik-tik flies) are large, biting flies that inhabit much of tropical Africa. Tsetse flies include all the species in the genus ''Glossina'', which are placed in their own family, Glos ...
fuscipes subspecies of the fly. The palpalis subspecies contributes the majority of the rest of the cases. The different subspecies of fly dominate different habitats. For instance, the Glossina Morsitans subspecies inhabits
savanna A savanna or savannah is a mixed woodland-grassland (i.e. grassy woodland) biome and ecosystem characterised by the trees being sufficiently widely spaced so that the canopy does not close. The open canopy allows sufficient light to reach th ...
hs while the Glossina Palpalis subspecies prefers woody
riverine A river is a natural stream of fresh water that flows on land or inside caves towards another body of water at a lower elevation, such as an ocean, lake, or another river. A river may run dry before reaching the end of its course if it run ...
habitats. However, all flies are susceptible to extremes in temperature (outside of the 16-40 degree Celsius range). Furthermore, trypanosomes are only able to reproduce in tsetse flies between the 25 to 30 Celsius range. These factors mean that only a minority of tsetse flies, around 20 percent, are estimated to carry
trypanosomes Trypanosomatida is a group of kinetoplastid unicellular organisms distinguished by having only a single flagellum. The name is derived from the Greek language, Greek ''trypano'' (borer) and ''soma'' (body) because of the corkscrew-like motion of ...
. These flies can also adapt to human activity, thus causing changes in disease patterns. For example, when brush is cleared for
agriculture Agriculture encompasses crop and livestock production, aquaculture, and forestry for food and non-food products. Agriculture was a key factor in the rise of sedentary human civilization, whereby farming of domesticated species created ...
, the flies can retreat into the savannah and conversely when humans move into brush, the flies will reproduce and feed more frequently. As a result, large increases of population associated with expansion into woody habitats often coincides with trypanosomiasis
epidemic An epidemic (from Greek ἐπί ''epi'' "upon or above" and δῆμος ''demos'' "people") is the rapid spread of disease to a large number of hosts in a given population within a short period of time. For example, in meningococcal infection ...
s. Traditionally, cattle herders in East Africa were well aware of the effects of the tsetse flies and avoided these areas or set fire to the bush in order to clear the area of the flies and infected animals. The equilibrium was disturbed in the colonial era leading to multiple epidemics. Humans, their livestock, or wild animals can all act as
reservoirs A reservoir (; ) is an enlarged lake behind a dam, usually built to store fresh water, often doubling for hydroelectric power generation. Reservoirs are created by controlling a watercourse that drains an existing body of water, interrup ...
of trypanosomiasis disease. However, the reservoirs used differ based on subspecies of trypanosoma
protozoa Protozoa (: protozoan or protozoon; alternative plural: protozoans) are a polyphyletic group of single-celled eukaryotes, either free-living or parasitic, that feed on organic matter such as other microorganisms or organic debris. Historically ...
ns and thus the variants of trypanosomiasis disease. There are two main variants of trypanosomoiasis which are in turn transmitted by different
subspecies In Taxonomy (biology), biological classification, subspecies (: subspecies) is a rank below species, used for populations that live in different areas and vary in size, shape, or other physical characteristics (Morphology (biology), morpholog ...
of the trypanosome protozoans. Trypanosoma brucei rhodiense tends to result in more acute forms of disease and is mainly transmitted form one human to another. Most patients with this variant of disease will die within six months of infection.
Cattle Cattle (''Bos taurus'') are large, domesticated, bovid ungulates widely kept as livestock. They are prominent modern members of the subfamily Bovinae and the most widespread species of the genus '' Bos''. Mature female cattle are calle ...
can also act as a reservoir in areas where disease incidence is lower. Trypanosoma brucei gambiense is the second type of protozoan which usually results in more chronic disease patterns. Its main reservoir is the cattle populations. Although it is also fatal, death can take months or years to occur. Geographical separation of these two variants of trypanosomes occurs along the
Rift Valley A rift valley is a linear shaped lowland between several highlands or mountain ranges produced by the action of a geologic rift. Rifts are formed as a result of the pulling apart of the lithosphere due to extensional tectonics. The linear ...
. Trypanosoma brucei rhodiense is usually found on the eastern side of the valley while the gambiense variant resides on the western side. The ranges of the two disease variants could overlap in
Uganda Uganda, officially the Republic of Uganda, is a landlocked country in East Africa. It is bordered to the east by Kenya, to the north by South Sudan, to the west by the Democratic Republic of the Congo, to the south-west by Rwanda, and to the ...
,
Tanzania Tanzania, officially the United Republic of Tanzania, is a country in East Africa within the African Great Lakes region. It is bordered by Uganda to the northwest; Kenya to the northeast; the Indian Ocean to the east; Mozambique and Malawi to t ...
, and Congo in the future.  


Research

Trypanosomiasis could, in future be prevented by genetically altering the tsetse fly. As the tsetse fly is the main vector of transmission, making the fly immune to the disease by altering its genome could be the main component in an effort to eradicate the disease. New technologies such as CRISPR allowing cheaper and easier genetic engineering could allow for such measures. A pilot program in
Senegal Senegal, officially the Republic of Senegal, is the westernmost country in West Africa, situated on the Atlantic Ocean coastline. It borders Mauritania to Mauritania–Senegal border, the north, Mali to Mali–Senegal border, the east, Guinea t ...
, funded by the
International Atomic Energy Agency The International Atomic Energy Agency (IAEA) is an intergovernmental organization that seeks to promote the peaceful use of nuclear technology, nuclear energy and to inhibit its use for any military purpose, including nuclear weapons. It was ...
, has considerably reduced the tsetse fly population by introducing male flies which have been sterilized by exposure to
gamma ray A gamma ray, also known as gamma radiation (symbol ), is a penetrating form of electromagnetic radiation arising from high energy interactions like the radioactive decay of atomic nuclei or astronomical events like solar flares. It consists o ...
s. This has allowed a change of
cattle breed Over 1000 breeds of cattle are recognized worldwide, some of which adaptation, adapted to the local climate, others which were bred by humans for specialized uses. Cattle breeds fall into two main types, which are regarded as either two closely ...
s from lower producing
trypanotolerant A trypanotolerant organism is one which is relatively less affected by trypanosome infestation. By host In livestock Some breeds are known for their trypanotolerance. This is especially important in Africa where a few particular trypanosom ...
breeds to higher-producing foreign breeds, and was selected as one of the Best Sustainable Development Practices on Food Security by EXPO Milan 2015.


Other animals

*
Nagana Animal trypanosomiasis, also known as nagana and nagana pest, or sleeping sickness, is a disease of non-human vertebrates. The disease is caused by trypanosomes of several species in the genus ''Trypanosoma'' such as '' T. brucei'' (which also ...
, or animal African trypanosomiasis, also called 'Souma' or 'Soumaya' in
Sudan Sudan, officially the Republic of the Sudan, is a country in Northeast Africa. It borders the Central African Republic to the southwest, Chad to the west, Libya to the northwest, Egypt to the north, the Red Sea to the east, Eritrea and Ethiopi ...
. *
Surra Surra (from the Marathi language, Marathi ''sūra'', meaning the sound of heavy breathing through nostrils, of imitative origin) is a disease of vertebrate animals. The disease is caused by protozoan trypanosomes, specifically ''Trypanosoma e ...
* Mal de cadeiras, or Quebra Bunda (of central South America,
Brazil Brazil, officially the Federative Republic of Brazil, is the largest country in South America. It is the world's List of countries and dependencies by area, fifth-largest country by area and the List of countries and dependencies by population ...
) * Murrina de caderas (of Panama; Derrengadera de caderas) * Dourine * Cachexial fevers (various) * Gambian horse sickness (of central Africa) * Baleri (of Sudan) * Kaodzera (Rhodesian trypanosomiasis) * Tahaga (a disease of
camel A camel (from and () from Ancient Semitic: ''gāmāl'') is an even-toed ungulate in the genus ''Camelus'' that bears distinctive fatty deposits known as "humps" on its back. Camels have long been domesticated and, as livestock, they provid ...
s in Algeria) * Galziekte, galzietzke (bilious fever of cattle; gall sickness of South Africa) * Peste-boba (of Venezuela; Derrengadera) Some species of cattle such as the
African buffalo The African buffalo (''Syncerus caffer)'' is a large sub-Saharan African bovine. The adult African buffalo's horns are its characteristic feature: they have fused bases, forming a continuous bone shield across the top of the head, referred to ...
,
N'dama N'Dama is a breed of cattle from West Africa. Other names for them include Boenca or Boyenca (Guinea-Bissau), Fouta Jallon, ''Djallonké'' or ''Djallonké cattle'', Fouta Longhorn, Fouta Malinke, Futa, Malinke, Mandingo (Liberia), and N'Dama Peti ...
, and Keteku appear trypanotolerant and do not develop symptoms. Calves are more resistant than adults. Tsetse-borne species of trypanosomes have entered
zoo A zoo (short for zoological garden; also called an animal park or menagerie) is a facility where animals are kept within enclosures for public exhibition and often bred for conservation purposes. The term ''zoological garden'' refers to zoology, ...
s outside the traditional tsetse zone in infected animals imported for the zoo.


References


Bibliography

* * * *


External links


Animal Trypanosomosis
reviewed and published by Wikivet.
Disease card
on
World Organisation for Animal Health The World Organisation for Animal Health (WOAH), formerly the (OIE), is an intergovernmental organisation founded in 1924, coordinating, supporting and promoting animal disease control. The primary objective of WOAH is to control epizootic dis ...
{{Authority control Protozoal diseases