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United States Department of Agriculture

Agricultural Research Service

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Location: Animal Parasitic Diseases Laboratory

2013 Annual Report

1a. Objectives (from AD-416):
The NAHMS program includes periodic national commodity studies to investigate current issues and examine general health and management practices used on farms. These studies are driven by industry and stakeholder interest, and collect information that is not available from any other source.

1b. Approach (from AD-416):
Activities will include testing of sera from lambs for antibodies to Toxoplasma gondii by using the modified agglutination test (MAT) during the National Animal Health Monitoring System (NAHMA) Sheep 2011 study.

3. Progress Report:
Toxoplasmosis is the cause of economic losses to sheep producers across the U.S. and is also a threat to human health. As part of the Sheep 2011 study, blood was collected from 4,009 market age lambs (3-12 months of age) from 359 operations in the 22 largest sheep producing States in order to estimate the seroprevalence of T.gondii in market age lambs on U.S. sheep operations. Sera were shipped from the National Veterinary Service Laboratory to ARS scientists in Beltsville, MD and were tested for antibodies to T. gondii using the modified agglutination test. Results showed that of the lambs tested, 477 (11.9%) tested positive with a titer of 25 or above. Lambs in the west had the greatest seroprevalence (17.9%) followed by the east (10.6%) and central U.S. (6.1%). The seroprevalence was 13.1% in small and medium operations with 20-499 ewes and 6.4% in operations with 500 or more ewes. By flock type, seroprevalence was 13.8% in operations that managed their sheep on pasture compared with 4.4% in open range flocks. Of the 359 operations that participated in the testing, 45.4% (163) had at least one seropositive animal. By flock size, operation-level prevalence was greatest among operations with 100-499 ewes (48.6%), followed by operations with 20-99 ewes (45.6%) and 500 or more ewes (35.3%). Operation-level prevalence was greatest among operations in the west (58.8%) followed by the east (42.6%) and central U.S. (31.7%). The observed differences in this study between flocks managed on pasture compared with open range flocks and in flocks with fewer than 500 ewes may be accounted for by greater environmental exposure to T. gondii through the presence of feral and domestic felids and rodents on and near pastures, and to smaller operations that are less intensively managed than feedlots. These data will interest veterinarians, epidemiologists and producers interested in understanding and limiting human food-borne risk of acquiring Toxoplasmosis.

4. Accomplishments

Last Modified: 06/23/2017
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