The Prepatent and Patent Periods of Fasciola hepatica in Cattle in Puerto Rico

Abstract

Fasciola hepatica, the liver fluke, is the most important parasite of cattle in Puerto Rico. Although it was commonly found in cattle at the turn of the century, no quantitative information is available. More recently, investigatioiis have shown that the prevalence of bovine fascioliasis in the slaughterhouses in Puerto Rico has been rising with an overall prevalence rate of 32% (Frame and Bendezu, 1978, J. Parasitol. 64: 136). Fascioliasis represents economic losses of over a million dollars because of condemned cow liver alone. NMoreover, the estimated prevalence is considered conservative as fecal examinations have shown even higher prevalence rates (Frame et al., 1981, J. Parasitol. 66: 698-699). Studies on the epidemiology of bovine fascioliasis in Puerto Rico have been reported (Chiriboga et al., 1980, J. Agri. Univ. P.R. 64: 93-106; Frame et al., 1981, loc. cit.). However, (no stud(lies have been done on the prepatent and patent periods of infection with F. hepatica in cattle in Puerto Rico. The present study was designed to examine this aspect. Three calves, approximately 6 mo old and free of intestinal helminth eggs, were infected per os with 1,000 F. hepatica metacercariae in sealed gelatin capsules. The cysts were fresh and obtained from laboratory-reared Lyilnaea cubensis snails. The calves were kept in individual raised paddocks, fed with hay grown locally and with concentrate feed. Fecal samples were collected in the morning every 2 wk for 56 wk, and a quantitative fecal sedimentation technique was used to determine the number of F. hepatica eggs eliminated per gram of feces (Dennis et al., 1954, JAVMA 124: 47-50). All three calves were first excreting F. hepatica eggs by the 8th wk of infection (1 to 9 eggs/g), and egg excretion peaked (220 to 510 eggs/g) at 18 to 20 wk postinfection, when the number began decreasing rapidly (Table I). By the 40th wk (10 imo) of infection, a second significant drop in egg counts was observed in which only one to seven F. hepatica eggs/g were noted with the egg excretion level dropping to zero to two eggs/g by 46 wk postinfection. Thus, it is possible that the last surviving flukes died by the 40th wk of infection and the eggs observed were those deposited and stored in the gallbladder. It is known that the gallbladder excretes bile during certain periods of the day when the cows are ruminating. Thus, excretion of eggs remaining in the gallbladder would decrease slowly as shown in the table. These studies demonstrated that the prepatent period of F. hepatica in cattle in Puerto Rico was 8 wk postinfection, with maximum egg production occurring by 18 to 20 wk postinfection. It appears that cows with a primary infection of F. hepatica lose