Graduate Thesis Or Dissertation
 

Pathogenicity of experimentally induced concurrent infections of Fasciola hepatica and Haemonchus contortus in sheep

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  • Twenty yearling sheep were allotted to four groups, each containing five sheep of approximately equal weight. On experimental days 0, 1, 2, 3, and 4, each sheep in each group was given the following inoculations by stomach tube: five sheep in group I (Fasciola hepatica-exposed controls) were given approximately 120 F. hepatica metacercariae each day; five sheep in group II (Haemonchus contortus-exposed controls) were given approximately 10,000 H. contortus infective larvae (L₃) each day; five sheep in group III (F. hepatica and. H. contortus-exposed principals) were given approximately 120 F. hepatica metacercariae and 10,000 H. contortus L₃ each day; five sheep in group IV (nonexposed controls) were given sham doses of tap water each day. Each sheep was weighed at seven-day intervals until experimental day 203 and a fecal sample collected until day 105. Clinicopathologic changes in blood were analyzed in samples collected from each sheep at seven-day intervals. Sheep that died in groups land III were necropsied; gross pathology was recorded, helminths recovered, and liver tissue taken for histo-pathologic examination. Two sheep in group I were killed and examined on experimental days 269 and 1, 063. Clinicopathologic and pathologic changes in F. hepatica-exposed sheep (group I) were characteristic of chronic fascioliasis. Eosinophilia, leukocytosis, hypoalbuminemia, and progressive macrocytic, normochromic anemia occurred before time of death. One sheep each died on experimental days 162, 168, and 265; 412, 414, and 318 mature F. hepatica were recovered in liver bile ducts. Fluke burdens in two sheep that were killed and necropsied on experimental days 269 and 1, 063 were 383 and 28, respectively. Resistance to H. contortus exposure was evident in group II sheep; four of five sheep acquired patent infections and two of these were negative for nematode eggs in feces on experimental day 70. Transitory mild eosinophilia and hypoalbuminemia, and normocytic, hypochromic anemia was found, but each sheep recovered naturally within 203 days. Enhanced pathogenicity of simultaneous exposure to F. hepatica and H. contortus in sheep was demonstrated by death of three sheep in group III before experimental day 80. The two remaining sheep in group III died two months before two sheep in group I that harbored similar fluke burdens. A macrocytic, slightly hypochromic anemia was found in one sheep that died on experimental day 51; 253 immature F. hepatica and 28, 000 H. contortus were recovered at necropsy. Slightly microcytic, hypochromic anemia, characteristic of H. contortus infection, was found in two sheep that died on experimental days 71 and 78. In one sheep, 238 F. hepatica and 25, 300 H. contortus were recovered; the other sheep harbored 332 and 18,100 helminths, respectively. The two remaining sheep died on experimental days 190 and 201; anemia was macrocytic and normochromic, characteristic of chronic fascioliasis. Burdens were 346 and 326 mature F. hepatica; 12,600 and 27,600 H. contortus were recovered. Establishment of both helminths and host response to F. hepatica infection appeared normal, but development of host resistance to H. contortus was inhibited by simultaneous F. hepatica infection. Eosinophilic response in sheep, with the concurrent infections was less than that of sheep with F. hepatica infection alone.
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