Editing Tsetse fly (section)

==Trypanosomiasis==
[[File:Trypanosoma sp. PHIL 613 lores.jpg|thumb|[[Trypanosomes]] in a blood smear]]

Tsetse are [[Vector (epidemiology)|biological vectors]] of [[trypanosomes]], meaning that in the process of feeding, they acquire and then transmit small, single-celled trypanosomes from [[infection|infected]] [[vertebrate]] [[host (biology)|hosts]] to uninfected animals. Some tsetse-transmitted trypanosome species cause [[trypanosomiasis]], an infectious disease. In humans, tsetse transmitted trypanosomiasis is called [[African trypanosomiasis|sleeping sickness]].<ref>{{cite web |title=Trypanosomiasis, human African (sleeping sickness) |url=https://www.who.int/en/news-room/fact-sheets/detail/trypanosomiasis-human-african-(sleeping-sickness) |website=www.who.int |access-date=14 May 2020 |language=en}}</ref> In animals, tsetse-vectored trypanosomiases include ''nagana'', ''souma'' (a French term which may not be a distinct condition<ref name="Battista-Researchgate">{{ cite web | url=https://www.researchgate.net/publication/40893277 | title=Capanna E. Battista Grassi entomologist and the Roman School of Malariology. Parassitologia. 2008 Dec;50(3-4):201-11. PMID: 20055229.
 }}</ref>), and ''[[surra]]'' according to the animal infected and the trypanosome species involved. The usage is not strict and while ''nagana'' generally refers to the disease in cattle and horses it is commonly used for any of the animal trypanosomiases.

Trypanosomes are animal [[parasite]]s, specifically [[protozoa]]ns of the genus ''Trypanosoma''. These organisms are about the size of red blood cells. Different species of trypanosomes infect different hosts. They range widely in their effects on the vertebrate hosts. Some species, such as ''T. theileri'', do not seem to cause any health problems except perhaps in animals that are already sick.<ref name="Hoare">{{cite book |author=C. A. Hoare |chapter=Systematic Description of the Mammalian Trypanosomes of Africa |editor1=H. Mulligan |editor2=W. Potts |year=1970 |title=The African Trypanosomiases |publisher=London, UK: [[Allen and Unwin|George Allen and Unwin Ltd.]] |isbn=0-04-614001-8}}</ref>

Some [[strain (biology)|strains]] are much more [[virulence|virulent]]. Infected flies have an altered salivary composition which lowers feeding efficiency and consequently increases the feeding time, promoting trypanosome transmission to the vertebrate host.<ref>{{cite journal |title=Trypanosoma brucei Modifies the Tsetse Salivary Composition, Altering the Fly Feeding Behavior That Favors Parasite Transmission|journal=[[PLOS Pathogens]] |year=2010 |volume=6 |issue=6 |author1=Jan Van Den Abbeele |author2=Guy Caljon |author3=Karin De Ridder |author4=Patrick De Baetselier |author5=Marc Coosemans |doi=10.1371/journal.ppat.1000926 |pmid=20532213 |pages=e1000926|pmc=2880569 |doi-access=free }}</ref> These trypanosomes are highly evolved and have developed a life cycle that requires periods in both the vertebrate and tsetse hosts.

Tsetse transmit trypanosomes in two ways, mechanical and biological transmission.
*Mechanical transmission involves the direct transmission of the same individual trypanosomes taken from an infected host into an uninfected host. The name 'mechanical' reflects the similarity of this mode of transmission to mechanical injection with a [[syringe]]. Mechanical transmission requires the tsetse to feed on an infected host and acquire trypanosomes in the blood meal, and then, within a relatively short period, to feed on an uninfected host and regurgitate some of the infected blood from the first blood meal into the tissue of the uninfected animal. This type of transmission occurs most frequently when tsetse are interrupted during a blood meal and attempt to satiate themselves with another meal. Other flies, such as [[horse-fly|horse-flies]], can also cause mechanical transmission of trypanosomes.<ref>{{cite journal |title=Seasonal prevalence of bovine trypanosomosis in a tsetse-infested zone and a tsetse-free zone of the Amhara Region, north-west Ethiopia |journal=Onderstepoort Journal of Veterinary Research|year=2004 |volume=71 |issue=4 |pages=307–12 |author1=T. Cherenet |author2=R. A. Sani |author3=J. M. Panandam |author4=S. Nadzr |author5=N. Speybroeck |author6=P. van den Bossche |pmid=15732457 |doi=10.4102/ojvr.v71i4.250|doi-access=free }}</ref>
*Biological transmission requires a period of incubation of the trypanosomes within the tsetse host. The term 'biological' is used because trypanosomes must reproduce through several generations inside the tsetse host during the period of incubation (development within the fly is known as the extrinsic incubation period), which requires extreme [[Adaptation (biology)|adaptation]] of the trypanosomes to their tsetse host. In this mode of transmission, trypanosomes reproduce through several generations, changing in morphology at certain periods. This mode of transmission also includes the sexual phase of the trypanosomes. Tsetse are believed to be more likely to become infected by trypanosomes during their first few blood meals. Tsetse infected by trypanosomes are thought to remain infected for the remainder of their lives. Because of the adaptations required for biological transmission, trypanosomes that can be transmitted biologically by tsetse cannot be transmitted in this manner by other insects.

The relative importance of these two modes of transmission for the propagation of tsetse-vectored trypanosomiases is not yet well understood. However, since the sexual phase of the trypanosome life cycle occurs within the tsetse host, biological transmission is a required step in the life cycle of the tsetse-vectored trypanosomes.

The cycle of biological transmission of trypanosomiasis involves two phases, one inside the tsetse host and the other inside the vertebrate host. Trypanosomes are not passed between a pregnant tsetse and her offspring, so all newly emerged tsetse adults are free of infection. An uninfected fly that feeds on an infected vertebrate animal may acquire trypanosomes in its proboscis or gut. These trypanosomes, depending on the species, may remain in place, move to a different part of the digestive tract, or migrate through the tsetse body into the salivary glands. When an infected tsetse bites a susceptible{{dubious | reason=Unlikely to selectively transmit only to susceptible hosts |date=October 2020}} host, the fly may regurgitate part of a previous blood meal that contains trypanosomes, or may inject trypanosomes in its saliva. Inoculation must contain a minimum of 300 to 450 individual trypanosomes to be successful, and may contain up to 40,000 cells.<ref name="Hoare"/>

In the case of ''T. b. brucei'' infecting ''G. p. gambiensis'', during this time the parasite changes the [[proteome]] contents of the fly's head. This may be the reason/a reason for the behavioral changes seen, especially the unnecessarily increased feeding frequency, which increases transmission opportunities. This may be due in part to the altered [[glucose]] metabolism observed, causing a perceived need for more calories. (The metabolic change, in turn, being due to complete absence of [[Glucose-6-phosphate dehydrogenase|glucose-6-phosphate 1-dehydrogenase]] in infected flies.) [[Monoamine neurotransmitter]] synthesis is also altered: Production of [[aromatic L-amino acid decarboxylase]] - involved in [[dopamine]] and [[serotonin]] synthesis - and [[α-methyldopa hypersensitive protein]] was induced. This is very similar to the alterations in ''other'' [[fly|dipteran]] vectors' head proteomes under infection by ''other'' eukaryotic parasites of mammals, found in another study by the same team in the same year.<ref name="Lefevre-et-al-2007">{{cite journal | last1=Lefèvre | first1=T. | last2=Thomas | first2=F. | last3=Ravel | first3=S. | last4=Patrel | first4=D. | last5=Renault | first5=L. | last6=Le Bourligu | first6=L. | last7=Cuny | first7=G. | last8=Biron | first8=D. G. | title=''Trypanosoma brucei brucei'' induces alteration in the head proteome of the tsetse fly vector ''Glossina palpalis gambiensis'' | journal=[[Insect Molecular Biology]] | publisher=[[Royal Entomological Society]] ([[Wiley Publishing|Wiley]]) | volume=16 | issue=6 | date=2007-12-17 | issn=0962-1075 | doi=10.1111/j.1365-2583.2007.00761.x | pages=651–660 | pmid=18092995 | s2cid=3134104| url=https://hal.archives-ouvertes.fr/hal-02308250 }}</ref>

The trypanosomes are injected into vertebrate muscle tissue,{{citation needed|date=December 2015}} but make their way, first into the [[lymphatic system]], then into the bloodstream, and eventually into the brain. The disease causes the swelling of the lymph glands, emaciation of the body, and eventually leads to death. Uninfected tsetse may bite the infected animal prior to its death and acquire the disease, thereby closing the transmission cycle.

===Disease hosts and vectors===

The tsetse-vectored trypanosomiases affect various vertebrate species including humans, antelopes, bovine cattle, camels, horses, sheep, goats, and pigs. These diseases are caused by several different trypanosome species that may also survive in wild animals such as crocodiles and monitor lizards. The diseases have different distributions across the African continent, so are transmitted by different species. This table summarizes this information:<ref name="Hoare"/><ref>{{cite web |author=R. C. Hunt |year=2004 |url=http://www.med.sc.edu:85/trypanosomiasis.htm |title=Trypanosomiasis page, "Microbiology and Immunology On-line" |publisher=[[University of South Carolina]] |access-date=2005-04-02 }}{{Dead link|date=September 2018 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>
{| class="wikitable"
|-
! Disease !! Species affected !! ''Trypanosoma'' agents !! Distribution !! ''Glossina'' vectors
|-
| '''[[African trypanosomiasis|Sleeping sickness]]''' — chronic form || humans || ''T. brucei gambiense'' || Western Africa ||
* ''G. palpalis''
* ''G. tachinoides''
* ''G. fuscipes''
* ''G. morsitans''
|-
| '''[[African trypanosomiasis|Sleeping sickness]]''' — acute form || humans || ''T. brucei rhodesiense'' || Eastern Africa ||
* ''G. morsitans''
* ''G. swynnertoni''
* ''G. pallidipes''
* ''G. fuscipes''
|-
| '''[[Nagana]]''' — acute form || antelope<br />cattle<br />camels<br />horses || ''T. brucei brucei'' || Africa ||
* ''G. morsitans''
* ''G. swynnertoni''
* ''G. pallidipes''
* ''G. palpalis''
* ''G. tachinoides''
* ''G. fuscipes''
|-
| '''[[Nagana]]''' — chronic form || cattle<br />camels<br />horses || ''T. congolense'' || Africa ||
* ''G. palpalis''
* ''G. morsitans''
* ''G. austeni''
* ''G. swynnertoni''
* ''G. pallidipes''
* ''G. longipalpis''
* ''G. tachinoides''
* ''G. brevipalpis''
|-
| '''[[Nagana]]''' — acute form || domestic pigs<br />cattle<br />camels<br />horses || ''T. simiae''<ref name="CABI-ISC">{{ cite web | url=http://www.cabi.org/isc/datasheet/60778 | title=Trypanosoma simiae - CABI Invasive Species Compendium|website=Cabi.org}}</ref> || Africa ||
* ''G. palpalis''
* ''G. fuscipes''
* ''G. morsitans''
* ''G. tachinoides''
* ''G. longipalpis''
* ''G. fusca''
* ''G. tabaniformis''
* ''G. brevipalpis''
* ''G. vanhoofi''
* ''G. austeni''
|-
| '''[[Nagana]]''' — acute form || cattle<br />camels<br />horses || ''T. vivax'' || Africa ||
* ''G. morsitans''
* ''G. palpalis''
* ''G. tachinoides''
* ''G. swynnertoni''
* ''G. pallidipes''
* ''G. austeni''
* ''G. vanhoofi''
* ''G. longipalpis''
|-
| '''[[Surra]]''' — chronic form || domestic pigs<br />[[warthog]]<br/>—(''Phacochoerus aethiopicus'')<br />forest hogs<br/>—(''[[Hylochoerus]] spp.'') || ''T. suis'' || Africa ||
* ''G. palpalis''
* ''G. fuscipes''
* ''G. morsitans''
* ''G. tachinoides''
* ''G. longipalpis''
* ''G. fusca''
* ''G. tabaniformis''
* ''G. brevipalpis''
* ''G. vanhoofi''
* ''G. austeni''<ref>{{Cite journal |last1=Desquesnes |first1=Marc |last2=Holzmuller |first2=Philippe |last3=Lai |first3=De-Hua |last4=Dargantes |first4=Alan |last5=Lun |first5=Zhao-Rong |last6=Jittaplapong |first6=Sathaporn |date=2013 |title=Trypanosoma evansi and surra: a review and perspectives on origin, history, distribution, taxonomy, morphology, hosts, and pathogenic effects |journal=BioMed Research International |volume=2013 |pages=194176 |doi=10.1155/2013/194176 |doi-access=free |issn=2314-6141 |pmc=3760267 |pmid=24024184}}</ref>
|}

=== In humans ===
{{main article|African trypanosomiasis}}
Human African trypanosomiasis, also called [[African trypanosomiasis|sleeping sickness]], is caused by trypanosomes of the species ''Trypanosoma brucei''. This disease is invariably fatal if left untreated, but can almost always be cured with current medicines if the disease is diagnosed early enough.

Sleeping sickness begins with a tsetse bite leading to an inoculation in the subcutaneous tissue. The infection moves into the [[lymphatic system]], leading to a characteristic swelling of the lymph glands called ''Winterbottom's sign''.<ref>{{Cite web|url=https://sc.edu/study/colleges_schools/medicine/education/basic_science_departments/pathology_microbiology_and_immunology/index.php|title=Pathology, Microbiology and Immunology - School of Medicine {{pipe}} University of South Carolina|website=Sc.edu|access-date=12 November 2020}}</ref> The infection progresses into the blood stream and eventually crosses into the [[central nervous system]] and invades the [[brain]] leading to extreme [[lethargy]] and eventually to [[death]].

The species ''Trypanosoma brucei'', which causes the disease, has often been subdivided into three subspecies that were identified based either on the vertebrate hosts which the strain could infect or on the virulence of the disease in humans. The trypanosomes infectious to animals and not to humans were named ''Trypanosoma brucei brucei''. Strains that infected humans were divided into two subspecies based on their different virulences: ''Trypanosoma brucei gambiense'' was thought to have a slower onset and ''Trypanosoma brucei rhodesiense'' refers to strains with a more rapid, virulent onset. This characterization has always been problematic but was the best that could be done given the knowledge of the time and the tools available for identification. A recent molecular study using [[restriction fragment length polymorphism]] analysis suggests that the three subspecies are [[polyphyletic]],<ref>{{cite journal |author=G. Hide |year=1999 |title=History of Sleeping Sickness in East Africa |journal=[[Clinical Microbiology Reviews]] |volume=12 |issue=1 |pages=112–125|doi=10.1128/CMR.12.1.112 |pmid=9880477 |pmc=88909 |doi-access=free }}</ref> so the elucidation of the strains of ''T. brucei'' infective to humans requires a more complex explanation. [[Procyclin]]s are [[protein]]s developed in the surface coating of trypanosomes whilst in their tsetse fly vector.<ref>{{Cite journal|doi=10.1073/pnas.98.4.1513 |pmid=11171982|title=The surface coat of procyclic Trypanosoma brucei: Programmed expression and proteolytic cleavage of procyclin in the tsetse fly|year=2001|last1=Acosta-Serrano|first1=A. |last2=Vassella|first2=E.|last3=Liniger|first3=M.|last4=Renggli|first4=C. K.|last5=Brun|first5=R. |last6=Roditi|first6=I.|last7=Englund|first7=P. T.|journal=Proceedings of the National Academy of Sciences |volume=98|issue=4|pages=1513–1518 |bibcode=2001PNAS...98.1513A|pmc=29288|doi-access=free}}</ref>{{clarify |reason=This seems unrelated. Are these molecules the sequencing targets that suggested ''brucei'' is not one species? Otherwise why is this mentioned here. |date=October 2020}}

Other forms of human trypanosomiasis also exist but are not transmitted by tsetse. The most notable is American trypanosomiasis, known as [[Chagas disease]], which occurs in [[South America]], caused by ''Trypanosoma cruzi'', and transmitted by certain insects of the [[Reduviidae]], members of the [[Hemiptera]].

===In domestic animals===
{{main article|Animal trypanosomiasis}}
Animal [[trypanosomiasis]], also called ''nagana'' when it occurs in [[cattle|bovine cattle]] or [[horse]]s or ''sura'' when it occurs in domestic [[pig]]s, is caused by several trypanosome species. These [[disease]]s reduce the growth rate, [[milk]] productivity, and strength of [[farm]] animals, generally leading to the eventual [[death]] of the infected animals. Certain species of cattle are called ''[[trypanotolerance|trypanotolerant]]'' because they can survive and grow even when infected with trypanosomes although they also have lower productivity rates when infected.

The course of the disease in animals is similar to the course of [[African trypanosomiasis|sleeping sickness]] in humans.

''Trypanosoma congolense'' and ''Trypanosoma vivax'' are the two most important species infecting bovine cattle in [[sub-Saharan Africa]]. ''Trypanosoma simiae'' causes a virulent disease in [[swine]].

Other forms of animal trypanosomiasis are also known from other areas of the globe, caused by different species of trypanosomes and transmitted without the intervention of the tsetse fly.

The tsetse fly vector ranges mostly in the central part of Africa.

[[Trypanosomiasis]] poses a considerable constraint on livestock agricultural development in tsetse fly-infested areas of sub-Saharan Africa, especially in West and Central Africa. International research conducted by [[ILRI]] in [[Nigeria]], the [[Democratic Republic of the Congo]] and [[Kenya]] has shown that the [[N'Dama]] is the most resistant breed.<ref>{{Cite web |last=Agyemang |first=K. |year=2004 |title=Trypanotolerant livestock in the context of trypanosomiasis intervention strategies |url=https://openknowledge.fao.org/handle/20.500.14283/y5832e |access-date= |series=PAAT Technical and Scientific Series, No. 7. |publisher=FAO |publication-place=Rome}}</ref><ref>{{Cite web|url=https://www.slideshare.net/mobile/ILRI/animal-genetic-resources-characterization-and-conservation-research-in-africa-an-overview|title=Animal genetic resources characterization and conservation research i...|website=Slideshare.net|date=9 January 2012|access-date=12 November 2020}}</ref>