Abstract
Black rats act as a reservoir host for many human and animal diseases; therefore, we encouraged to study the prevalence of the parasites in rats. This study investigated the internal and external parasites of 45 trapped rats in the period between May 2018 and April 2019 from El-Behera Governorate, the western region of Nile Delta, Egypt. All Rattus rattus rats were examined parasitologically to detect the prescence of parasites and their effects on the tissue. The prevalence was 82.2% for internal parasites and 44.4% for flea. The prevalence showed a high infection rate of nematodes infection with 66.66% and the detected species were Syphacia muris and Gongylonema neoplasticum. Syphacia muris was detected in 57.78% and Gongylonema neoplasticum was detected in 26.67% while 8.89% of rats only were reported with mixed infection with the two species of nematodes. The infection with Trematoda (Mesostephanus spp.) was 24.44%. Cestoda had the lowest infection rate of 11.11% which was reported as Cysticercous fasciolaris. Concerning the locality, the prevalence of parasites was highest in El- Dalangat (35.56%) and lowest in Damanhour (17.78%). Concerning the effect on host tissues, intestinal villi of rats showed desquamation of the lining epithelium and leukocytic infiltration in lamina propria. In the liver, the larva of C. fasciolaris was appeared attached to the hepatic tissue surrounded with a very thin membranous structure. This study presented the prevalence of the parasites, their identification in black rats, and histopathological changes in some infected tissues. These results may be of value for public health or veterinary interest.

Key words: Rattus rattus, El-Behera, Egypt, Parasites, Hepatic tissue