Hemostatic Parameters of the Blood of Cotton Rats, Sigmodon hispidus, Infected with Parastrongylus costaricensis (Metastrongyloidea: Angiostrongylidae)

Abstract

The hemostatic parameters of adult male cotton rats infected with 20-25 third-stage larvae of Parastrongylus costaricensis were compared with those of ageand sex-matched control animals. The normal range for whole blood clotting times was 85-140 seconds. The parasitic infection caused a decrease in these clotting times. The coagulation assays, performed on the plasma of animals infected for 30-40 days, showed decreases in factors VII, X, XI, and XII and an increase in fibrinogen. The activated partial thromboplastin time was elevated; however, the decrease in prothrombin time was not significant. These findings imply that the blood of cotton rats becomes hypercoagulable following infection, and this may be a defence mechanism facilitating repair of the vascular bed of the intestine when damaged by hatching and movement of the larvae. Adult Parastrongylus costaricensis (Morera & Cespedes, 1971) Ubelaker, 1986, a metastrongylid nematode, occur in the subserosal arteries of the cecum or in the ileocecocolic branch of the cranialmesenteric artery of the major host, a cotton rat, (Sigmodon hispidus). Occasionally, they are found in other mammals including humans (Morera & Cespedes, 1971; Tesh et al., 1973; Ubelaker, 1986). The life cycle is indirect, and cotton rats, as well as humans, become infected by ingesting molluscan intermediate hosts or vegetation containing mucus from snails contaminated with infectious third-stage larvae. The larvae then invade mesenteric lymph nodes where they undergo third and fourth molts. Eleven days following infection, the juvenile worms migrate to the adjacent mesenteric arteries and develop to sexual maturity. In the cotton rat, eggs are deposited by the female worms beginning 18 days after infection and the eggs become trapped in the capillary bed of the cecum. In normal hosts, such as cotton rats, the prepatent period is completed by the twenty-fourth day when larvae hatch from the eggs, traverse the intestinal mucosa, and exit the host in the feces. In unnatural hosts, such as humans, the larvae do not hatch and are destroyed by an intense inflammatory reaction (Morera, 1973; Tesh et al., 1973). Blood coagulation abnormalities have been found in animals infected with other parasites that occur in the blood stream. Tsang & Damian (1977) reported 1 The authors express their appreciation to Ms. J. Winford, and Ms. J. Roberts for excellent technical assistance and to Professor Richard Gunst for his interest and assistance in the statistical analysis. 2 Department of Special Hematology, Baylor University Medical Center, Dallas, Texas 75246,