Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide







  • Last modified
  • 15 May 2019
  • Datasheet Type(s)
  • Animal Disease
  • Preferred Scientific Name
  • surra
  • Overview
  • Trypanosoma evansi is a protozoan parasite that is the causative agent of the animal disease surra.  The disease occurs in a wide area from the northern part of Africa through the Middle East to Southeast Asia;...

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Preferred Scientific Name

  • surra

International Common Names

  • English: surra, trypanosoma evansi, in cattle - exotic; surra, trypanosoma evansi, in pigs - exotic; Trypanosoma evansi infection
  • Spanish: mal de caderas; murrina

Local Common Names

  • North Africa: el debab ; el gafar ; mbori; tabourit


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Trypanosoma evansi is a protozoan parasite that is the causative agent of the animal disease surra.  The disease occurs in a wide area from the northern part of Africa through the Middle East to Southeast Asia; it is thought to have been introduced to the Americas in the 16th century and is now found in much of Latin America except the southernmost parts.  It is not known to occur in North America (except Mexico), Australia, Europe (except for rare introductions into Spain and France), or northern Russia. It affects a very large range of domestic and wild animals; only one case of human infection has been reported. It has a significant economic and animal health impact on cattle, camels and other livestock in many countries. T. evansi is mechanically transmitted primarily by several species of haematophagous flies (mainly Tabanids and Stomoxes), but in Latin America the vampire bat (Desmodus rotundus) is a vector and reservoir host.  Clinical manifestations of disease include fever, anaemia, loss of appetite, weight loss, nervous signs, abortion, cachexia, and potentially death.  No vaccine is available.  Several chemotherapeutic drugs are used for the prophylaxis and treatment of surra; however, drug resistance is known to occur. Surra is on the OIE list of notifiable diseases. For further information on this disease from OIE, see the website:

Hosts/Species Affected

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Trypanosoma evansi has one of the widest host ranges among the trypanosomes.  While almost all mammalian species are susceptible to infection with T. evansi, only certain ones develop significant clinical signs and play a role in its epidemiology.  Their susceptibility, however, varies greatly depending on host geography, host species, and parasite strain (Desquesnes et al., 2013).  In Africa and the Middle East, T. evansi is mainly a parasite of camels, but it is also highly pathogenic in the Equidae (horses, asses, mules, and donkeys).  In Asia, it is a major parasite for water buffaloes (Bubalus bubalis) (in contrast, it is not pathogenic in the African buffalo Syncerus caffer).  Surra is also considered to be an economically important disease in cattle, pigs, and goats in many parts of Asia.  T. evansi has also been found in elephants in India and Thailand.  In Australia, Europe, and the New World, T. evansi is an important threat to horses, cattle, pigs, camels (in Australia), and other livestock species.  In addition to domestic hosts, T. evansi has been found in a wide range of wildlife species around the world (Desquesnes et al., 2013).  In Central and South America, it has been found in various marsupials, primates, lagomorphs, rodents, perissodactyls, and artiodactyls; however, their epidemiological importance, if any, has not been fully established (Herrera et al., 2004). Note that only a selection of hosts is shown in the Host Animals table.

The Latin American vampire bat (Desmodus rotundus) is an interesting example of a species simultaneously being a host, reservoir, and a vector -- it can mechanically transmit the parasite in its saliva, and also act as a true reservoir, maintaining the parasite in the bat colony in the absence of other hosts (Hoare, 1965).


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Trypanosoma evansi has the widest geographical distribution among the trypanosomes.  In the Eastern Hemisphere, its geographical distribution is continuous from the northern part of Africa through the Middle East to Southeast Asia.  In Africa, it is present in all countries where camels are present.  It is found in sub-Saharan and Mediterranean climates, as well as in arid deserts and semiarid steppes.  It is present in the Arabian Peninsula, Turkey, Afghanistan, Pakistan, and has been occasionally reported from Bulgaria (Desquesnes et al., 2013).  It is also present throughout southern Asia, including India, China, Mongolia, parts of Russia, Bhutan, Nepal, Myanmar, Laos, Vietnam, Cambodia, Thailand, Malaysia, the Philippines, and Indonesia (Luckins, 1988).  Its presence was suspected in Papua New Guinea, but not confirmed, and it is so far absent from Australia (Reid, 2002) (it was briefly introduced there in the early 20th century but was soon eradicated -- Desquesnes et al., 2013, citing Hoare, 1972). In Latin America, it is present in much of South America other than the southernmost parts, and it is uncertain how far north through Central America its range extends -- some reports suggest Mexico, but this is not certain (Desquesnes, 2004). In Europe, there have been recent introductions of T. evansi in the Canary Islands (Spain) (Gutiérrez et al., 1998), the Spanish mainland (Tamarit et al., 2010), and a single epizootic in France resulting from infected camels imported from the Canary Islands (Desquesnes et al., 2008).  The parasite is absent from North America, northern Europe, and northern Russia (Desquesnes et al., 2013).

Distribution Table

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The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.

Continent/Country/RegionDistributionLast ReportedOriginFirst ReportedInvasiveReferenceNotes


AfghanistanPresentOIE, 2009; Desquesnes et al., 2013
ArmeniaDisease not reportedOIE, 2009
AzerbaijanDisease not reportedOIE, 2009
BahrainDisease never reportedOIE, 2009
BangladeshPresentOIE, 2009; Misra et al., 2016
BhutanPresentLuckins, 1988; OIE, 2009
Brunei DarussalamNo information availableOIE Handistatus, 2005
CambodiaPresentLuckins, 1988; OIE, 2009
ChinaPresentLuckins, 1988; OIE, 2009
-Hong KongNo information availableOIE, 2009
Georgia (Republic of)Disease never reportedOIE Handistatus, 2005
IndiaPresentHoare, 1972; OIE, 2009
IndonesiaPresentLuckins, 1988; OIE, 2009
IranRestricted distributionOIE, 2009
IraqPresentOIE, 2009; Desquesnes et al., 2013
IsraelPresentOIE, 2009; Desquesnes et al., 2013
JapanDisease not reportedOIE, 2009
JordanPresentOIE, 2009; Desquesnes et al., 2013
KazakhstanPresentOIE, 2009; Desquesnes et al., 2013
Korea, DPRDisease not reportedOIE Handistatus, 2005
Korea, Republic ofDisease never reportedOIE, 2009
KuwaitDisease not reportedOIE, 2009
KyrgyzstanDisease never reportedOIE, 2009
LaosPresentLuckins, 1988; OIE, 2009
LebanonPresentOIE, 2009; Desquesnes et al., 2013
MalaysiaPresentLuckins, 1988; OIE, 2009
MongoliaPresentLuckins, 1988; OIE, 2009
MyanmarPresentLuckins, 1988; OIE, 2009
NepalPresentLuckins, 1988; OIE, 2009
OmanPresentOIE, 2009; Desquesnes et al., 2013
PakistanPresentOIE, 2009; Desquesnes et al., 2013
PhilippinesPresentLuckins, 1988; OIE, 2009
QatarNo information availableOIE, 2009
Saudi ArabiaPresentOIE, 2009; Desquesnes et al., 2013
SingaporeDisease never reportedOIE, 2009
Sri LankaDisease not reportedOIE, 2009
SyriaPresentOIE, 2009; Desquesnes et al., 2013
TaiwanDisease not reportedOIE Handistatus, 2005
TajikistanDisease not reportedOIE, 2009
ThailandPresentLuckins, 1988; OIE, 2009
TurkeyPresentOIE, 2009; Desquesnes et al., 2013
TurkmenistanDisease not reportedOIE Handistatus, 2005
United Arab EmiratesPresentOIE, 2009; Desquesnes et al., 2013
UzbekistanDisease not reportedOIE Handistatus, 2005
VietnamPresentLuckins, 1988; OIE, 2009
YemenNo information availableOIE, 2009


AlgeriaPresentHoare, 1972; OIE, 2009
AngolaNo information availableOIE, 2009
BeninNo information availableOIE, 2009
BotswanaDisease never reportedOIE, 2009
Burkina FasoPresentHoare, 1972; OIE, 2009
BurundiDisease never reportedOIE Handistatus, 2005
CameroonNo information availableOIE Handistatus, 2005
Cape VerdeDisease never reportedOIE Handistatus, 2005
Central African RepublicDisease not reportedOIE Handistatus, 2005
ChadPresentHoare, 1972; OIE, 2009
CongoNo information availableOIE, 2009
Congo Democratic RepublicDisease not reportedOIE Handistatus, 2005
Côte d'IvoireDisease not reportedOIE Handistatus, 2005
DjiboutiDisease not reportedOIE, 2009
EgyptPresentHoare, 1972; OIE, 2009
EritreaPresentHoare, 1972; OIE, 2009
EthiopiaPresentHoare, 1972; OIE, 2009
GabonNo information availableOIE, 2009
GambiaNo information availableOIE, 2009
GhanaNo information availableOIE, 2009
GuineaNo information availableOIE, 2009
Guinea-BissauNo information availableOIE, 2009
KenyaPresentHoare, 1972; OIE, 2009
LesothoDisease never reportedOIE, 2009
LibyaPresentHoare, 1972; OIE Handistatus, 2005
MadagascarDisease never reportedOIE, 2009
MalawiDisease not reportedOIE, 2009
MaliPresentHoare, 1972; OIE, 2009
MauritaniaPresentHoare, 1972
MauritiusDisease never reportedOIE, 2009
MoroccoPresentHoare, 1972; OIE, 2009
MozambiqueDisease not reportedOIE, 2009
NamibiaDisease never reportedOIE, 2009
NigerPresentHoare, 1972
NigeriaPresentHoare, 1972; OIE, 2009
RéunionDisease never reportedOIE Handistatus, 2005
RwandaNo information availableOIE, 2009
Sao Tome and PrincipeDisease not reportedOIE Handistatus, 2005
SenegalPresentHoare, 1972; OIE, 2009
SeychellesDisease not reportedOIE Handistatus, 2005
SomaliaPresentHoare, 1972; OIE Handistatus, 2005
South AfricaDisease never reportedOIE, 2009
-Canary IslandsPresentIntroduced1995Gutiérrez et al., 1998
SudanPresentHoare, 1972; OIE, 2009
SwazilandDisease never reportedOIE, 2009
TanzaniaNo information availableOIE, 2009
TogoNo information availableOIE, 2009
TunisiaPresentHoare, 1972; OIE, 2009
UgandaNo information availableOIE, 2009
ZambiaNo information availableOIE, 2009
ZimbabweDisease never reportedOIE, 2009

North America

BermudaDisease not reportedOIE Handistatus, 2005
CanadaDisease never reportedOIE, 2009
GreenlandDisease never reportedOIE, 2009
MexicoAbsent, reported but not confirmedIntroducedDesquesnes, 2004; OIE, 2009
USADisease never reportedOIE, 2009

Central America and Caribbean

BarbadosDisease never reportedOIE Handistatus, 2005
BelizeDisease never reportedOIE, 2009
British Virgin IslandsDisease never reportedOIE Handistatus, 2005
Cayman IslandsDisease never reportedOIE Handistatus, 2005
Costa RicaAbsent, reported but not confirmedIntroducedDesquesnes, 2004; OIE, 2009
CubaDisease never reportedOIE, 2009
CuraçaoDisease not reportedOIE Handistatus, 2005
DominicaDisease not reportedOIE Handistatus, 2005
Dominican RepublicDisease never reportedOIE, 2009
El SalvadorDisease never reportedOIE, 2009
GuadeloupeNo information availableOIE, 2009
GuatemalaAbsent, reported but not confirmedIntroducedDesquesnes, 2004; OIE, 2009
HaitiDisease never reportedOIE, 2009
HondurasAbsent, reported but not confirmedIntroducedDesquesnes, 2004; OIE, 2009
JamaicaDisease not reportedOIE, 2009
MartiniqueDisease not reportedOIE, 2009
NicaraguaAbsent, reported but not confirmedIntroducedDesquesnes, 2004; OIE, 2009
PanamaPresentIntroducedDesquesnes, 2004; OIE, 2009
Saint Kitts and NevisDisease never reportedOIE Handistatus, 2005
Saint Vincent and the GrenadinesDisease never reportedOIE Handistatus, 2005
Trinidad and TobagoDisease never reportedOIE Handistatus, 2005

South America

ArgentinaPresentIntroducedOIE, 2009; Desquesnes et al., 2013
BoliviaPresentIntroducedDesquesnes, 2004; OIE, 2009
BrazilPresentIntroduced Invasive Desquesnes, 2004; OIE, 2009As of 2004, spreading in Brazil with considerable clinical and economic consequences in newly infected regions
ChileLocalisedIntroducedDesquesnes, 2004; OIE, 2009
ColombiaWidespreadIntroducedDesquesnes, 2004; OIE, 2009
EcuadorAbsent, reported but not confirmedIntroducedDesquesnes, 2004; OIE, 2009
Falkland IslandsDisease never reportedOIE Handistatus, 2005
French GuianaPresent, few occurrencesIntroducedDesquesnes, 2004; OIE, 2009One case in a dog suggests presence in wild animals
GuyanaAbsent, formerly present1970IntroducedDesquesnes, 2004; OIE Handistatus, 2005
ParaguayPresentIntroducedDesquesnes, 2004; OIE Handistatus, 2005
PeruPresentIntroducedDesquesnes, 2004; OIE, 2009
SurinamePresent, few occurrencesIntroducedDesquesnes, 2004A few reports in dogs; some PCR evidence of presence in cattle
UruguayDisease never reportedOIE, 2009
VenezuelaPresentIntroducedDesquesnes, 2004; OIE, 2009Enzootic throughout plains


AlbaniaNo information availableOIE, 2009
AndorraDisease never reportedOIE Handistatus, 2005
AustriaNo information availableOIE, 2009
BelarusDisease never reportedOIE, 2009
BelgiumDisease not reportedOIE, 2009
Bosnia-HercegovinaDisease not reportedOIE Handistatus, 2005
BulgariaPresent, few occurrencesOIE, 2009; Desquesnes et al., 2013
CroatiaDisease never reportedOIE, 2009
CyprusDisease never reportedOIE, 2009
Czech RepublicDisease not reportedOIE, 2009
DenmarkDisease never reportedOIE, 2009
EstoniaDisease never reportedOIE, 2009
FinlandDisease never reportedOIE, 2009
FrancePresent, few occurrencesIntroduced2006Desquesnes et al., 2008; OIE, 2009
GermanyDisease never reportedOIE, 2009
GreeceDisease never reportedOIE, 2009
HungaryDisease never reportedOIE, 2009
IcelandDisease never reportedOIE, 2009
IrelandDisease never reportedOIE, 2009
Isle of Man (UK)Disease never reportedOIE Handistatus, 2005
ItalyNo information availableOIE, 2009
JerseyDisease never reportedOIE Handistatus, 2005
LatviaDisease never reportedOIE, 2009
LiechtensteinDisease not reportedOIE, 2009
LithuaniaDisease never reportedOIE, 2009
LuxembourgDisease not reportedOIE, 2009
MacedoniaDisease never reportedOIE, 2009
MaltaDisease never reportedOIE, 2009
MoldovaDisease never reportedOIE Handistatus, 2005
MontenegroDisease never reportedOIE, 2009
NetherlandsDisease never reportedOIE, 2009
NorwayDisease never reportedOIE, 2009
PolandDisease never reportedOIE, 2009
PortugalDisease not reportedOIE, 2009
RomaniaDisease never reportedOIE, 2009
Russian FederationPresentOIE, 2009Present based on regional distribution
-Southern RussiaPresentDesquesnes et al., 2013
-Western SiberiaPresentDesquesnes et al., 2013
SerbiaNo information availableOIE, 2009
SlovakiaDisease not reportedOIE, 2009
SloveniaNo information availableOIE, 2009
SpainPresent, few occurrencesIntroducedOIE, 2009; Tamarit et al., 2010
SwedenDisease never reportedOIE, 2009
SwitzerlandDisease never reportedOIE, 2009
UKDisease not reportedOIE, 2009
-Northern IrelandDisease never reportedOIE Handistatus, 2005
UkraineDisease never reportedOIE, 2009
Yugoslavia (former)No information availableOIE Handistatus, 2005
Yugoslavia (Serbia and Montenegro)Disease not reportedOIE Handistatus, 2005


AustraliaDisease never reportedOIE, 2009
French PolynesiaDisease not reportedOIE, 2009
New CaledoniaDisease never reportedOIE, 2009
New ZealandDisease never reportedOIE, 2009
SamoaDisease never reportedOIE Handistatus, 2005
VanuatuDisease never reportedOIE Handistatus, 2005
Wallis and Futuna IslandsNo information availableOIE Handistatus, 2005


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Anaemia is a common feature of clinical trypanosomiasis with Trypanosoma evansi.  It appears to be predominantly haemolytic, associated with decreased life span of erythrocytes and extensive erythrophagocytosis (Habila et al., 2012).  The onset of anaemia is related to the appearance of trypanosomes in the blood, and the severity is associated with the level and initial wave of parasitaemia.  Haemolytic factors such as free fatty acids, immunologic mechanisms, haemodilution, coagulation disorders, depression of erythrogenesis and release of trypanosomal sialidase have all been implicated in the development of anaemia in trypanosomiasis (Habila et al., 2012).  The anaemia in both human and animal trypanosomiases is, however, predominantly the result of haemolytic crises in which the erythrocytes are destroyed by an expanded mononuclear phagocytic system (Igbokwe and Mohammed, 1991).  The destruction of erythrocytes is in part due to the action of sialidase, which cleaves sialic acids on the cell surface and exposes galactosyl residues.  These residues are then recognized by D-galactose-specific lectins on macrophages, leading to erythrophagocytosis and subsequently anaemia (Sallau et al., 2008).

Another of the important aspects of T. evansi infection and surra is immunosuppression.  Primarily, this allows the trypanosomes to survive and multiply in extracellular fluids, especially in the blood.  The best-known immune “escape” mechanism developed by trypanosomes is the antigenic variation caused by their variant surface glycoproteins (VSGs) (Cross, 1975; Vickerman, 1969).  VSGs are the main antigenic determinant for the host immune system, and so antigenic variation in T. evansi appears to be the primary mechanism for evasion of the hosts’ immune responses (Habila et al., 2012).  The key features underlying successful immune evasion are clone-specific singular VSG expression combined with switching from one VSG to another (Horn, 2014).  The VSG coat accounts for about 10% of the total protein of the parasite, and the genome contains approximately 1000 VSG genes, which are randomly switched on and off at each generation (Habila et al., 2012).  Significantly, this antigenic variation in the VSG has prevented development of a protective vaccine and permits reinfections when animals are exposed to a new antigenic type.


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The general clinical signs of Trypanosoma evansi infection are not sufficiently pathognomonic for diagnosis.  Therefore, laboratory methods for detecting the parasite are required.  The classical direct parasitological methods for the diagnosis of trypanosomiasis, namely microscopic examination of blood or lymph node material, are useful, particularly in resource-limited countries, but they are not highly sensitive.  However, sensitivity can be increased significantly by using various concentration or amplification procedures (OIE, 2012).  Concentration procedures basically consist of centrifugation of heparinized capillary tubes of the suspected animal’s blood.  Trypanosomes concentrate at the junction between the buffy coat and the plasma, which can be observed under the microscope either directly through the glass capillary tube (Woo’s technique) or in a wet preparation using phase-contrast or dark-ground microscopy (Murray’s technique).  These methods have the added benefit of allowing the degree of anaemia (i.e., the haematocrit) to be estimated.

Laboratory animals may be used to reveal subclinical infections in domesticated animals.  T. evansi has a broad spectrum of infectivity for small rodents so rats and mice can be used.  Rodent inoculation using buffy coat material can detect as few as 1.25 T. evansi/ml blood (Reid et al., 2001).

In regions where other Trypanosoma spp. occur, specific identification by microscopy is not possible, and molecular methods are needed to specifically identify T. evansi.  Specific DNA probes have been used to detect trypanosome DNA in infected blood or tissue but are not routinely applied as further evaluation needs to be performed.  Polymerase chain reaction techniques are generally preferred and are routinely used in many laboratories.  The sensitivity of PCR is dependent on the amount of DNA in the sample, which is proportional to the level of parasitaemia.  In addition, DNA preparation is an important step that determines the success and the sensitivity of the PCR.  The test can be performed on whole blood, or preferably, on the buffy coat to increase the sensitivity.  Needle biopsy material or tissues of lungs, liver, or kidney obtained post mortem can also be used.  Numerous primer sets for both standard and real-time PCRs have been developed and evaluated for the detection of T. evansi DNA (OIE, 2012).

Similarly, many different serological tests have been developed to detect specific antibodies to trypanosomal antigens.  These include direct and indirect agglutination tests, complement fixation tests, indirect fluorescence antibody tests, and the trypanolysis test (OIE, 2012).  However, many of these tests are either useful only for small-scale surveys or are no longer used.  More recently, they have been replaced by the more sensitive and more easily standardized techniques of enzyme linked immunosorbent assay (ELISA) and the card agglutination test (CATT).  Evaluations of ELISA and CATT have been carried out in camels, horses, cattle, buffaloes, and pigs (Desquesnes et al., 2009; Diall et al., 1994; Holland et al., 2005; Reid and Copeman, 2003; Verloo et al., 2000).

List of Symptoms/Signs

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SignLife StagesType
Digestive Signs / Anorexia, loss or decreased appetite, not nursing, off feed Sign
General Signs / Fever, pyrexia, hyperthermia Sign
General Signs / Haemorrhage of any body part or clotting failure, bleeding Sign
General Signs / Mammary gland swelling, mass, hypertrophy udder, gynecomastia Sign
General Signs / Pale mucous membranes or skin, anemia Sign
General Signs / Petechiae or ecchymoses, bruises, ecchymosis Sign
General Signs / Swelling mass penis, prepuce, testes, scrotum Sign
General Signs / Weight loss Sign
Nervous Signs / Dullness, depression, lethargy, depressed, lethargic, listless Sign
Nervous Signs / Seizures or syncope, convulsions, fits, collapse Sign
Reproductive Signs / Abortion or weak newborns, stillbirth Sign
Skin / Integumentary Signs / Skin papules Sign
Skin / Integumentary Signs / Skin pustules Sign
Skin / Integumentary Signs / Skin vesicles, bullae, blisters Sign

Disease Course

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The clinical signs of Trypanosoma evansi infection can vary dramatically depending on host species.  Even within a host species, there can be variability in clinical signs in different geographical areas.  However, in general, disease signs include fever, anaemia, loss of appetite, weight loss, nervous signs, abortion, cachexia, and death.  Surra is primarily a disease of camelids and equines, in which the typical clinical disease course is described here.

In camels, signs of illness begin with intermittent fever (41°C) for about one week.  The animals appear dull and listless and become progressively weaker with loss of appetite and weight, develop oedema (particularly of the udder or scrotum), become anaemic, and develop petechial or ecchymotic haemorrhages.  Nervous signs are sometimes observed, including periodic convulsions.  The disease can be fatal, sometimes within a few months; however it is more often chronic and can frequently last 2-3 years (in parts of its rage it has been called Tibarsa, which means “three years disease” -- Desquesnes et al., 2013).

In horses, the incubation period is 1-4 weeks (sometimes up to 8 weeks), after which fever develops with high peaks (up to 44°C) corresponding to parasitaemia levels.  Other signs, such as weakness, lethargy, anemia, and severe weight loss follow.  Additionally, petechial haemorrhages on the eyelids and vulvar and vaginal mucosa can occur, as can haemorrhaging into the anterior chamber of the eye.  As in camels, abortion, nervous signs, and oedema of the abdomen, testicles or udder are clinical signs of surra in horses.  Other equines, such as donkeys, asses, and mules can become infected with T. evansi, but appear to have lower susceptibility compared to horses (Desquesnes et al., 2013).


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In contrast to the complex life cycle of Trypanosoma brucei, involving a vertebrate bloodstream stage and a procyclic stage in the tsetse fly, in Trypanosoma evansi a total or partial loss of kDNA has “locked” the trypanosome in the bloodstream form resulting in the elimination of the need for the tsetse fly vector, enabling mechanical transmission by a variety of vectors. This has resulted in its ability to leave the African tsetse fly belt and spread to other continents (Lai et al., 2008; Lun and Desser, 1995), allowing it, along with T. equiperdum, to become one of the pathogenic trypanosomes with the widest geographical distribution. Several species of haematophagous flies, including tabanids (Tabanus spp., Chrysops spp., and Haematopota spp.) and Stomoxes (Stomoxys spp.), are implicated in mechanically transferring infection from host to host. Flies in the genera Musca, Haematobia, and Atylotus can also serve as vectors, but tabanids (horse flies) are the most significant arthropod vectors.  The Latin American vampire bat (Desmodus rotundus) is mainly responsible for disseminating the parasite in Latin America.  The vampire bat is an interesting example of a species simultaneously being a host, reservoir, and a vector -- it can mechanically transmit the parasite in its saliva, and also act as a true reservoir, maintaining the parasite in the bat colony in the absence of other hosts (Hoare, 1965).  Carnivores may become infected after ingesting infected meat, and transmission in milk and during coitus has been documented (OIE, 2013).

Impact: Economic

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Several economically important animals, including camels, horses, buffaloes, and cattle, are particularly affected by surra (OIE, 2012).  Camels, for example, are a major part of the economies of many African and Middle East countries, being used for nomadic pastoralism, transportation, racing, and production of milk, wool and meat.  According to the United Nations Food and Agriculture Organization, the total world camel population is approximately 23 million animals (FAO, 2016), and surra is considered the most important single cause of morbidity and mortality in camels (OIE, 2013).  In addition to camels, Trypanosoma evansi and other livestock trypanosomes threaten 48 million cattle in 37 African countries and are responsible for major losses in the production of milk, meat, and manure fertilizer (Desquesnes et al., 2013).  In addition to Africa, T. evansi (and other animal trypanosomes) places a permanent constraint on raising livestock throughout much of Asia and Latin America.

Impact: Environmental

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While Trypanosoma evansi infects a wide range of domestic and wild animals, clinical disease (surra) mainly affects domestic livestock.  Although infected wildlife can become reservoir hosts (i.e. asymptomatic carriers), the impact of T. evansi on biodiversity and the environment is minimal.

Zoonoses and Food Safety

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In general, Trypanosoma evansi is thought to be a strictly animal pathogen and not considered to be a zoonotic concern.  However, in 2005 the first case of human trypanosomiasis caused by T. evansi was reported (Joshi et al., 2005).  The patient was a cattle farmer from a small village in central India.  He had intermittent fever associated with chills and sweating for 15 days.  He then developed signs of sensory deficit, and was disoriented and agitated with violent behavior.  It was speculated that the patient was probably contaminated through a wound on his finger when exposed to blood of infected cattle.  There was no central nervous system invasion by the parasites, and the patient was successfully treated with suramin.  Follow-up serological survey of the local population surrounding the patient’s village found 81 of 1806 (4.4%) people tested to be seropositive to T. evansi, suggesting exposure to the parasite in the study area (Shegokar et al., 2006).

While there is some epidemiological evidence that some carnivores, especially dogs, may be infected with T. evansi by eating contaminated meat (Desquesnes et al., 2013), there is no evidence suggesting that humans have been infected via contaminated food.  Because of this, and the rarity of human infection in general, T. evansi is not considered a food safety concern.

Disease Treatment

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Several drugs can be used for the prophylaxis and treatment of surra.  Prophylactic drugs include quinapyramine dimethylsulfate, prothridium and isometamidium chloride, and in some cases suramin.  As therapeutic treatments, quinapyramine sulfate, suramin, and diminazene aceturate can be used (OIE, 2013; Petersen and Grinnage-Pulley, 2015).  Only a few drugs, including melarsomine (Cymelarsan), quinapyramine sulfate (Triquin), and isometamidium chloride (Trypamidium-Samorin), have been approved for use in camelids (Wernery and Kaaden, 2002).  Many of the drugs used for cattle are either not curative or are too toxic for camels.  Overdosing quinapyramines, for example, can cause side effects in camels such as tremors, salivation and collapse leading to death (Wernery and Kaaden, 2002).  Drug resistance occurs and should be considered in refractory cases (Petersen and Grinnage-Pulley, 2015).  Thus, monitoring for drug resistance is important and should be employed when suspicion of resistance arises.

Prevention and Control

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Control of surra is difficult for a number of reasons.  Effective control of the disease is hampered by the lack of vector specificity and the wide range of hosts affected.  Due to the lack of vector specificity, control measures are often aimed at the host rather than the vector.  These can include detection and treatment of infected animals, prophylactic treatment of susceptible animals (although drug resistance is a continuing concern), and protection of animals from biting flies and (in Latin America) vampire bats (OIE, 2013).

There is no vaccine available for this disease.  Development of an effective vaccine is not likely in the near future due to the ability of the parasite to rapidly change its surface glycoproteins to avoid the host immune response.


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Carnes, J., Anupama, A., Balmer, O., Jackson, A., Lewis, M., Brown, R., Cestari, I., Desquesnes, M., Gendrin, C., Hertz-Fowler, C., Imamura, H., Ivens, A., Korený, L., Lai DeHua, MacLeod, A., McDermott, S. M., Merritt, C., Monnerat, S., Moon, W. J., Myler, P., Phan, I., Ramasamy, G., Sivam, D., Lun ZhaoRong, Lukeš, J., Stuart, K. (et al), 2015. Genome and phylogenetic analyses of Trypanosoma evansi reveal extensive similarity to T. brucei and multiple independent origins for dyskinetoplasty. PLoS Neglected Tropical Diseases, 9(1), e3404. doi: 10.1371/journal.pntd.0003404

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Japan: National Research Center for Protozoan Diseases, Obihiro University of Agriculture and Veterinary Medicine, Inada-cho Nishi 2-13 , Obihiro, Hokkaido 080-8555 ,

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20/01/2016 Original text by:

Chris Whitehouse, US Army Medical Research Institute of Infectious Diseases, Fort Detrick, Frederick, MD 21702-5011, USA.

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