False-positive Ascaris suum egg counts in pigs

• Published in: International journal for parasitology Vol. 27; no. 7; pp. 833 - 838
• Main Authors: Boes, Jaap, Nansen, Peter, Stephenson, Lani S.
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01.07.1997; Elsevier Science
• Subjects: Animals; Ascariasis - diagnosis; Ascariasis - parasitology; Ascariasis - veterinary; Ascaris suum; Ascaris suum - isolation & purification; Biological and medical sciences; coprophagia; False Positive Reactions; false-positive egg counts; Feces - parasitology; geophagia; Helminthic diseases; Infectious diseases; Intestinal Diseases, Parasitic - diagnosis; Intestinal Diseases, Parasitic - parasitology; Intestinal Diseases, Parasitic - veterinary; Medical sciences; Miscellaneous; Parasite Egg Count - veterinary; Parasitic diseases; Pigs; Predictive Value of Tests; Sensitivity and Specificity; Swine; Swine Diseases - diagnosis; Swine Diseases - parasitology; Pigs; Ascaris suum; false-positive egg counts; coprophagia; geophagia; False positive; Egg; Parasite; Coprophagy; Parasitosis; Helminthiasis; Pig; Infection; Ascariasis; Vertebrata; Experimental disease; Mammalia; Nematode disease; Helmintha; Nemathelminthia; Artiodactyla; Feces; Invertebrata; Nematoda; Ungulata; Counting
• ISSN: 0020-7519; 1879-0135
• DOI: 10.1016/S0020-7519(97)00054-4

False-positive Ascaris suum egg counts in pig faeces are frequently observed under both experimental and natural conditions. Data from 12 experiments with A. suum infections in pigs were summarized and showed that the percentage of false-positive faecal samples ranged from 4 to 36%. False-positive egg count values varied greatly between pigs and experiments (range 20–1060 eggs per gram faeces). Indoor experiments with pigs housed groupwise in pens generally produced more and higher false-positive egg counts, which may reflect differences in surface area and hence exposure to infective eggs, compared with pasture experiments. The positive predictive value (the number of pigs diagnosed positive by faecal sample that actually harboured worms) was low for indoor experiments (45%) compared with pasture experiments (89%). Differences in design for indoor experiments, such as floor type and use of bedding material, did not influence the positive predictive value (44–47%). A positive correlation was found ( r = 0.56, P < 0.05) between faecal egg counts of true-positive and false-positive pigs that were penned together. The results of this survey strongly support previous suggestions that false-positive A. suum egg counts in pigs are the result of coprophagia in indoor experiments and coprophagia/geophagia in pasture experiments. False-positive A. suum egg counts in pig faeces may vary greatly in prevalence and magnitude, and depend in part on management/housing factors.