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Development of diagnostics for T. evansi in camels and water-buffaloes: perspectives in vaccine development.

Alex Peniche peniche at BIOLOGIA.UNIVALLE.EDU.CO
Mon Apr 7 10:51:53 EST 1997

On 19 Mar 1997 biotec at goliat.ugr.es wrote:

> Development of diagnostics for T. evansi in camels and=20
> water-buffaloes:  perspectives in vaccine development.
> Trypanosoma evansi infections cause severe disease mainly in camels=20
> ("surra") and water buffaloes.  Periodically, severe outbreaks of=20
> trypanosomiasis also occur in horses and cattle although the=20
> organism can infect other domestic animals such as dogs, cats and=20
> pigs.  The T. evansi organism is transferred from animal to animal=20
> when biting flies are interrupted during feeding on an infected=20
> animal.  As a result, they quickly seek another animal in order to=20
> satisfy their food requirements and at the same time transfer=20
> trypanosomes to that animal.  T. evansi is regarded to have evolved=20
> from the morphologically identical Trypanosoma brucei group which=20
> include T.b. brucei infective to animals and T.b. rhodesiense, T.b.=20
> gambiense which are also responsible for "sleeping sickness" or=20
> "human African trypanosomiasis".   While the others undergo a=20
> cyclical development within their vector, the tsetse fly, T. evansi=20
> has lost this ability and relies on a purely mechanical transfer of=20
> the trypomastigote blood stage by biting flies and as a result has=20
> spread outside the tsetse fly-belt of tropical and sub-tropical=20
> Africa throughout North Africa, middle East, southern Russia and=20
> China, India, SE Asia, Indonesia and Philippines. It is also found=20
> in S. America where the disease is sometimes transmitted by=20
> infected vampire bats.
> =09
> In contrast to T. brucei, T. evansi isolates exhibit a major degree=20
> of similarity in their antigenic components and for this reason the=20
> development of a vaccine was contemplated, based on an=20
> infection/treatment regimen.  However, it was discovered that=20
> trypanocidal treatment released a product which stimulated the=20
> production of tumour necrosis factor which may cause death if=20
> released in excess amounts and work on a live vaccine was halted=20
> and the emphasis was moved to the development of accurate=20
> diagnostic tests of T. evansi infection.   =20
> =09
> In a European Union funded project (TS2 071) a diagnostic test=20
> based on the detection of trypanosome antibodies was developed - a=20
> card agglutination trypanosome test (CATT). This CATT is now in=20
> widespread use in the diagnosis of T. evansi infections and has=20
> been adapted to the diagnosis of human sleeping sickness.  However,=20
> a more specific and sensitive test was still desirable and the=20
> polymerase chain reaction (PCR) using specific portions of the=20
> trypanosome DNA molecule was used.  This test depends, firstly on=20
> identifying portions (base pairs) of DNA, from the nucleus (DNA) or=20
> from the kinetoplast (kDNA) which are specific for T. evansi. =20
> Utilising the PCR reaction a small amount of DNA present in a=20
> sample of blood or tissue can be replicated by the PCR until enough=20
> is present to be recognised on an electrophoretic gel.  A PCR DNA=20
> test has been developed and tested under field conditions in=20
> Thailand and Mali and is sensitive to 5 trypanosomes per 50 litres=20
> blood, and can be performed with non-sterile blood samples which=20
> have withstood temperatures of nearly 40oC for days.  The kDNA PCR=20
> has shown that all T. evansi isolates fall within four subtypes and=20
> indicate a identity with T. equiperdum, the sexually transmitted=20
> trypanosome causing =93dourine=94 in equines.
> =09
> The two unrelated findings that (a) T. evansi is capable of=20
> producing procyclin, which implies that mitochondrial activation is=20
> not necessary for procyclin production and (b) the dromedary camel=20
> produces two immunoglobulins devoid of light chains which still=20
> react with trypanosome antigens, may prove to have further=20
> scientific importance.
> =09
> For further information on this joint project of the University of=20
> Brussels, Mahidol University of Thailand and Laboratoire Central=20
> Veterinaire du Mali contact Prof R. Hamers, Institute of Molecular=20
> Biology, Vrije Univ0ersiteit Brussel, Belgium.

 e-mail: peniche at hypatia.univalle.edu.co

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