Effects of host sex and pregnancy on Trichinella Zimbabwensis infection in Sprague-Dawley rats and Balb C mice.
Trichinellosis is a zoonotic parasitic disease caused by nematode parasites of the genus Trichinella. Trichinella species infect a wide range of hosts including humans, domestic and wild animals. The main mode of human infection is through ingestion of raw or undercooked pork. The successful establishment and development of Trichinella parasite in a host is affected by various factors which include sex of host, environmental, immunological and hormonal. The objective of this study was to determine the effect of host sex and pregnancy on the establishment and development of Trichinella zimbabwensis in Sprague-Dawley rats and Balb C mice respectively. Rodents are the common reservoirs of Trichinella spp. in the domestic and sylvatic cycles and it was logical to determine the establishment and development of Trichinella zimbabwensis in Sprague-Dawley rats. The study on the effects of pregnancy and levels of progesterone and cortisol was done in Balb C mice and this was influenced by availability of mice in large quantities to conduct the experiments. Rats and mice are not widely different in their physiology and have been used interchangeably as host in previous Trichinella studies. Therefore it was important to use these animals as models for the study. In order to determine the effect of host sex on the establishment and development of T. zimbabwensis, 50 Sprague-Dawley rats were divided into two groups (25 males and 25 females) and orally infected with 7 Trichinella zimbabwensis muscle larvae per gram (LPG) of animal live weight. On days 5, 10, 15, 20 and 25 post-infection (PI), five animals from each group were sacrificed and the numbers of adult parasites in the intestine as well as larvae in muscles were determined. To determine the effect of host pregnancy, 90 female Balb C mice were divided into 3 groups of 30 mice each. Group 1 animals were orally infected with 50 LPG on day 0 of trial; group 2 animals were mated on day 0, but were not infected; group 3 animals were mated on day 0 and infected with 50 LPG on day 7 post-mating. On days 0, 7, 14, 21 and 28 PI for groups 1; days 0, 7, 14, 21 and 28 post-mating for group 2; and days 7, 14, 21, 28 and 35 post-mating for group 3, six animals from each group were sacrificed and the numbers of adult parasites in the intestines as well as larvae in the muscles were determined in infected groups. In addition, levels of the hormones progesterone and cortisol were measured in all groups at the same intervals. Results from the study showed a significantly higher number of Trichinella adults and larvae (P < 0.05) in male than in female Sprague-Dawley rats (four times higher adult worms and two times higher in muscle larvae in males than in females). On the other hand, pregnancy reduced the number of larvae establishing in muscles with progesterone levels significantly higher in pregnant than in non-pregnant Balb C mice (P < 0.05). This was attributed to the parasiticidal effect of progesterone against new-born larvae (NBL). This finding can be exploited when designing strategies to control and to treat the infection in rodents and humans. There were no significant differences in cortisol levels between pregnant and non-pregnant mice.