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United States Department of Agriculture

Agricultural Research Service

Title: PREVALENCE AND GENOTYPES OF GIARDIA DUODENALIS IN 1-2 YEAR-OLD DAIRY CATTLE

Authors
item Trout, James
item Santin-Duran, Monica
item Greiner, Ellis - UNIV OF FL, GAINESVILLE
item Fayer, Ronald

Submitted to: Veterinary Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 22, 2006
Publication Date: May 2, 2006
Citation: Trout, J.M., Santin, M., Greiner, E.C., Fayer, R. 2006. Prevalence and genotypes of Giardia duodenalis in 1-2 year-old dairy cattle. Veterinary Parasitology.

Interpretive Summary: Giardia duodenalis is an intestinal parasite of humans and domestic animals. DNA sequence analysis of isolates from different animal hosts indicates that there are different genotypes of Giardia even though they look identical when viewed through the microscope. These genotypes are referred to as Assemblages. Some of these Assemblages infect a wide range of animals, whereas other Assemblages appear to be adapted to a particular group of animals. Previous research in our laboratory that examined dairy cows from 1 week to 11 month of age indicated the presence of two genotypes: Assemblage E and Assemblage A. Assemblage E is infectious only for hoofed-livestock, whereas Assemblage A is infectious for humans and many other mammals. The occurrence of these genotypes in older dairy cows was previously unknown, thus the current study was undertaken to examine 1-2 year-old dairy cows for the presence of these Giardia genotypes. Fecal specimens were collected from adult cows on two farms each in Vermont, New York, Pennsylvania, Maryland, Virginia, North Carolina, and Florida. The specimens were subjected to PCR and DNA sequence analysis. Prevalence of Giardia infection ranged from 11% to 75% on 14 farms with an average prevalence of 36% (204 positive cattle out of 571 examined). DNA sequence analysis revealed that 91% of the 204 Giardia isolates were Assemblage E whereas9% were Assemblage A. The prevalence of these genotypes varied greatly from farm to farm, with four farms having exclusively Assemblage E Giardia. Overall, Assemblage E was present in 33% of all animals tested and Assemblage A was present in 3% of the animals. Thus, while many of the cows were infected with a genotype that is not known to be infectious for humans, 1-2 year old heifers on 10 of 14 farms did harbor Assemblage A Giardia. Therefore heifers in this age range should be considered a potential source of human infectious cysts in the environment, with some farms representing a much higher risk than others.

Technical Abstract: To determine the prevalence of Giardia genotypes in 12-24 month old dairy heifers, fecal specimens were collected from two farms each in Vermont, New York, Pennsylvania, Maryland, Virginia, North Carolina, and Florida. Specimens, cleaned of fecal debris and concentrated using CsCl density gradient centrifugation, were subjected to PCR and DNA sequence analysis. Prevalence of Giardia infection, ranged from 11% to 75% on on 14 farms with an average prevalence of 36% (204 positive cattle out of 571 examined). DNA sequence analysis of the 16S rRNA gene revealed 91% of the 204 Giardia isolates were Assemblage E, and 9% were Assemblage A. The prevalence of these genotypes varied greatly from farm to farm, with four farms having exclusively Assemblage E Giardia. Overall, Assemblage E was present in 33% of all animals tested and Assemblage A was present in 3% of the animals. Thus, while many of the cows were infected with a genotype that is not known to be infectious for humans, 1-2 year old heifers on 10 of 14 farms did harbor zoonotic Assemblage A Giardia. Therefore heifers cannot be overlooked as a potential source of human infectious cysts in the environment, with some farms representing a much higher risk than others.

Last Modified: 9/1/2014
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