Louise:
These single cell pathogens sound as if they could rival any character from
an Anne Rice novel. Trypanosoma evansi belongs to a group of flagellate
protozoa of the class Zoomastigophorea:Salivaria. They have complex life
cycles involving 2 hosts. These New World trophozoites live in the blood,
esophagus, intestine and then the salivary glands of their insect
vector-host (Tabanus) or horse fly. They proliferate as trypomastigotes in
the salivary glands of the fly, then are mechanically transmitted by bite to
the camel, elephant, horse, donkey or burro.
The clinical course of the infection is characterized by an increase in
numbers, followed by a sudden decrease in the population which is repeated
over a number of cycles. The remission coincides with an increase in host
protective antibody against specific surface expressed antigens , located in
the surface coat or glycocalyx.  The cyclic nature appears to occur due to
an almost endless change in the Varient Antigen Type (VAT). As a result, as
the host appears to be winning the battle, the parasite changes its variant
antigen coating and evades the host immune response allowing a resurgence of
the infection.
In Mexico and South America, T. evansi is also transmitted by the
blood-sucking Desmodus rotundus or vampire bat, whom preen and beg each
other to share the tablespoon of infected blood. The ancient Maya and Inca
also had their suspicions of the feared and revered flying God, whom shared
in their blood cult, attaching themselves to their livestock at night. Soon
after the bite, the victim would salivate, wither and die.
T. evansi in mammals causes "Surra" (heavy breathing sound), and translated
as rotten in India. It is also distributed throughout the Far East, North
Africa and Central and South America. Canines may also be infected by
feeding on contaminated carcasses, the pathogen invades their buccal mucosa.

Depending on the host, T. evansi can be detected and classified with
serology and PCR.  Histologically, it is demonstrated in spleen, bone marrow
and lymph node of their vertebrate hosts with a Giemsa (for parasites),
Wright stain or a methyl green pyronin (MGP).
On a lighter note...Happy Holidays!

Eric Kellar
Histology/Immunohistochemistry
University of Pittsburgh Medical Center


	From:  Louise Burrell [SMTP:lburrell@pathbox.wustl.edu]
	Sent:  Monday, December 14, 1998 3:59 PM
	To:  HistoNet Server
	Cc:  Laurie.Reilly@jcu.edu.au
	Subject:  Re:Hi old friend!!!

	Dear Laurie:
	I am having trouble getting thru to you.  My last e-mail was really
	meant(sent) to/for someone else.  please rite back--bad news re: my
uncle
	Paul.
	warmest regards for a lovely holiday season for you and your
family!!!
	What is Trypanosomes evansi???

	Love,

	 Beezie