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Internal Parasite Diagnosis in Livestock |  |
| Fresh fecal samples should be collected from livestock from pasture or, preferably, per rectum using plastic gloves (which may be inverted to act as a receptacle after sample collection). A representative number of herd samples should be collected from a minimum of 10 animals to account for the typical high individual variation in numbers of eggs shed. Samples can be combined after thorough mixing to enable examination of a single herd composite sample. |
| Quantitative fecal egg counts by the Wisconsin centrifugal flotation procedure or similar methods can be used to estimate relative infection burden for nematodes of the “GI parasite complex,” while also detecting coccidia and other parasites such as lungworm larvae and tapeworms. Three g of feces are placed in a container, suspended in ~15 mL water, strained through a gauze square into a 15 mL tube, and centrifuged (1,500 rpm for 3 min). The supernatant is decanted and the sediment
mixed with saturated sugar solution, filling the tube enough to form a positive meniscus before placing a 22 × 22 mm coverslip on the lip of the tube orifice. The tube is centrifuged again at low speed (1,500 rpm for 5 min). The coverslip, with the surface film containing eggs, is removed and transferred to a microscope slide for counting of trichostrongyle- and strongyle-type eggs. The total is divided by 3 to derive eggs/g (EPG). Other parasites are noted, if present, with a
general abundance designation of +1 (few), +2 (small number), +3 (large number), or +4 (too numerous to count). |
| A saturated solution of table salt (sg 1.20) is a cheap alternative medium for diagnosis of livestock parasites. Magnesium sulfate (sg 1.20) is the preferred medium for swine. Special slides containing chambers with etched areas of known volume are also used for estimating EPG, especially for small ruminants. Feces in a strained solution (usually saturated salt) are introduced into each chamber with a Pasteur pipette, and the eggs are counted under low-power magnification. A
commonly used counting slide is the McMaster slide, which has 2 chambers, each with a volume of 0.15 mL under the etched area. For example, if 3 g of feces are mixed with 42 mL of concentrate solution, then each egg counted is multiplied by 50 to yield the number of EPG in the fecal sample. Acceptable correlation between the EPG and the relative worm burden is often possible in young animals, although low (<5 EPG) or negative counts are typically found in adult animals. In young
cattle, which generally have EPG counts 10 times that of adult animals, EPG counts >50 reflect a moderate infection, and EPG counts >500 indicate a heavy burden and a need for treatment. |
| Because fluke eggs do not float readily, quantitative fecal sedimentation procedures are usually used. Two grams of feces are mixed with 35 mL soapy solution (2% liquid detergent) and strained through gauze into a 50-mL centrifuge tube. The tube is filled with soapy water and allowed to stand for 3 min, after which ½ of the supernatant is discarded. This is repeated 2-3 times until the supernatant is clean. All but 15 mL is poured off, 2 drops of new methylene blue are added, and
the eggs counted with a dissecting microscope in a gridded Petri dish or by examining several coverslipped microscope slides. The liver fluke,
Fasciola
, can be differentiated from
Paramphistomum
, the rumen fluke, by the golden color, more barreled shape, and slightly larger size of Fasciola versus the gray color, more pointed end, and smaller size of the usually nonpathogenic rumen fluke. Commercial sieve-sediment kits can reduce sample preparation time by 50%. In cattle,
Fasciola
EPG counts >3 suggest economic losses; EPG >10 may be associated with clinical signs. |
