| dc.description.abstract | This thesis is primarily a study of factors which influence
the virulence of T. (N). simiae for pigs. The factors
investigated include the species of tsetse vectors, size of
inocula of trypanosomes injected into pigs and the method of
maintenance of the trypanosomes. The rate of development of
T. (N). simiae in different species of tsetse and its
relationship to the resulting infection in pigs was also
investigated. In addition, an attempt was made to adapt
T. (N). simiae to laboratory rodents.
In this study three stocks of I. ().simiae were
cyclically transmitted through tsetse. Transmitting the isolates
through Glossina morsitans and Q. pallidipes resulted in a
disease less severe than did syringe inoculations. Pigs infected
through tsetse bites survived much longer than had previously
been reported, with some pigs exhibiting self-cure after running
infection for varying lengths of time. The response of pigs to
experimental infection with I. (~).simiae varied from one animal
to another and pigs appear to fall into three categories. Pigs
in the first group were the very susceptible and died during th0
first peak of parasitaemia. The parasitaemia built up fast and
Lhe pigs died soon after the first appearance of trypanosomes ill
the peripheral blood circulation.
VI
The second group developed parasitaem{a, and survived more than
one parasitaemia peak but eventually succumbed to the infection.
The third group became parasitaemic, apparently controlled the
parasitaemia for some weeks at very low levels and eventually
threw off the infection.
Grouping the pigs according to their place of origin shows
that those which experienced chronic, self-limiting infections
were from the same farm. The less susceptible pigs came from
this farm. This suggest that the course of infection observed
might have been determined by the ability of the individual pig
to control the infection rather than by the vector. No clear
evidence was obtained to show whether or not the species of the
vector influenced the virulence of T. (N). simiae.
Teneral tsetse flies became infected with T. (N). simiae
when they were fed on pigs carrying predominantly stumpy
trypanosomes in their blood, but the number of trypanosomes
circulating in blood did not appear to influence the infection
rate in tsetse.
At 2SoC G. morsitans developed mature T. (N). simiae
infections in 19 days and ~. pallidipes in 23 days.
G. morsitans was more frequently infected than Q. pallidipes.
In pigs neither the prepatent period nor the period of patency
appeared not to be related to the rate of development or the
infection rate in the tsetse fly.
VII
One isolate of T. (N). simiae (EATRO 1786) has been successfully
adapted to rats. The parasite has been maintained in rats
through 20 passages without pig serum and 14 passages with pig
serum. The infection first became lethal to rats in the seventh
passage. Abnormal trypanosomes were observed during the initial
stages of adaptation. The rat adapted I. (~).simiae were
shorter than trypanosomes from the original strain. Trypanosomes
from the original isolate had a mean length of range 13.5 pm
to 17. 43 ~m.',.Ln.rats the trypanosomes measured a
mean of 12.59 ~m (range 8.8 and 14.4 ~m). In pigs the rat
adapted T. (N). simiae measured a mean of 12.35 um (range
9.9 - 14.38 ~m). The rat adapted T. (N). simiae strain has
remained infective to tsetse and to pigs. It infects mice
readily. | en |
