Use of molecular tools to investigate the prevalence and transmission routes of Toxoplasma in woodmice and humans

Gerwash, OM

Abstract

Toxoplasma gondii is an important pathogen of humans and domestic livestock and is
a major cause of abortion. It is widely distributed amongst mammals and birds and the
epidemiology of human disease is complex due to the interactions between human
and animal hosts. Cats are the definitive host for the parasite and rodents are believed
to be involved in propagation of the parasite in cat populations. The aims of this study
were to use molecular biological methods to investigate parasite transmission in wild
rodents and humans.
In this study, the prevalence of Toxoplasma was determined in a natural population of
woodmice (Apodemus sylvaticus) which probably have infrequent interaction with
cats. The prevalence (49%) was compared with an urban rodent population (59%)
which definitely does interact with cats. No significant difference in prevalence was
found.
Toxoplasma gondii is found as three major clonal lineages - type I, II and III.
Although several methods exist for typing strains, these were not always found to be
sensitive enough to detect the parasite in infected tissue samples. In this study an
improved test for determining the strain types of Toxoplasma was developed based on
the "rep" DNA elements. This method could distinguish type I and II strains but could
not distinguish type III. As a more effective method for typing was published during
the course of this study, it was decided that no further effort would be invested in
attempting to modify the technique to work with type HI strains.
To investigate transmission routes for Toxoplasma in humans, a study was designed
to specifically measure vertical transmission. A collection of human DNA samples
was made from subjects in Miserata hospital in Libya. Following ethical consent procedures, DNA was extracted from foetal (umbilical cord) tissue discarded at birth
and transported to the UK for testing for Toxoplasma. One hundred and twenty three
samples were collected from 121 mothers. With the exception of two mothers, all of
the pregnancies were successful. Clinical records were obtained at the time of birth,
analysed and showed that the sample characteristics (eg birth rate, sex ratio etc)
appeared to be representative of the Libyan population in general. These samples
were tested for Toxoplasma, using the SAG-1 PCR system to determine the rate of
vertical transmission. The rate of vertical transmission in this cohort was found to be
20.1% which is very high compared to many published studies using serology. No
association of Toxoplasma infection was found with intra uterine foetal death
(abortion), previous abortion or pre-eclampsia toxaemia. The results are discussed in
the light of other published literature.

Citation

Gerwash, O. Use of molecular tools to investigate the prevalence and transmission routes of Toxoplasma in woodmice and humans. (Thesis). University of Salford

• Thesis Type: Thesis
• Deposit Date: Aug 18, 2021
• Award Date: Jun 1, 2007