United States Department of Agriculture • Animal and Plant Health Inspection Service • Safeguarding American Agriculture

Veterinary Services

Centers for Epidemiology and Animal Health June 2011

_________________________________________________________________________________________________________________________

Seroprevalence of Trichinella

and Toxoplasma in U.S. 

Grower/Finisher Pigs, 2006

Background

Toxoplasma gondii is a protozoan parasite capable 

of infecting most warm-blooded animals, including 

humans. It is estimated that 60 million people in the 

United States are infected with T. gondii, although 

few demonstrate symptoms, as competent immune 

systems prevent clinical disease (toxoplasmosis).

1

Toxoplasma can be a threat to public health. 

Infections in pregnant women may result in the birth 

of blind and mentally disabled children. Immunesuppressed adults can also suffer damage to the 

eyes and brain due to reactivation of a latent 

Toxoplasma infection.

Cats are a reservoir for Toxoplasma and once 

infected shed oocysts in their feces for 

approximately 1 to 2 weeks.

2 Animals and humans 

can be infected by ingesting soil, water, or plant 

material contaminated with the oocysts. Humans 

can also be infected by consuming undercooked 

meat, such as pork and lamb, infected with 

Toxoplasma. 

Toxoplasma is of concern to the pork industry. 

Clinical toxoplasmosis can cause respiratory 

disease in nursing pigs and reproductive problems 

in sows, including mummified fetuses or stillborn 

piglets. Few pigs display disease signs associated 

with Toxoplasma infections, even though the 

parasite can persist in the edible tissues of the pigs 

for the life of the animals. Toxoplasma in meat is 

readily destroyed by cooking to certain 

temperatures, freezing, or irradiation. 

Controlling Toxoplasma infections in pigs

consists of keeping cats and their feces away from 

pig and feed storage areas, preventing cannibalism 

of dead pigs, controlling rodents, and not feeding 

uncooked garbage to pigs.

Swine 2006 study

In 2006, the USDA’s National Animal Health 

Monitoring System (NAHMS) conducted a study on 

swine health and management practices from a 

random sample of swine production sites in 17 

States in 4 regions.*

Producers participating in the NAHMS Swine 

2006 study were asked to submit up to 35 blood 

samples from grower/finisher pigs to be tested for 

antibodies to Toxoplasma and Trichinella. From 

September 5, 2006, through March 15, 2007, 6,238 

samples were collected from 185 swine sites and 

tested at the Beltsville Agricultural Research Center 

using an enzyme-linked immunosorbant assay test. 

These sites represented over 

90 percent of operations with 100 or more pigs in 

the United States and nearly 94 percent of the U.S. 

pig inventory. One goal of the Swine 2006 study 

was to estimate the prevalence of Toxoplasma and

Trichinella on U.S. swine operations.

This information sheet presents Trichinella

results and compares prevalence of Toxoplasma at 

the pig level and herd level.

Trichinella prevalence

Sera samples were tested in duplicate for the 

presence of antibodies to Trichinella using a 

commercial ELISA as recommended by the 

manufacturer (SafePath Laboratories, Carlsbad, 

CA). The sera were tested at a 1:200 dilution, and 

positive and negative control pig sera supplied by 

the manufacturer were included on each ELISA 

plate. All 6,235 samples tested were negative.

 * Regions:

North: Michigan, Minnesota, Pennsylvania, and Wisconsin

West Central: Colorado, Kansas, Missouri, Nebraska, and 

South Dakota

East Central: Illinois, Indiana, Iowa, and Ohio

South: Arkansas, North Carolina, Oklahoma, and Texas
United States Department of Agriculture • Animal and Plant Health Inspection Service • Safeguarding American Agriculture

Toxoplasma prevalence—pig-level 

Overall, 2.7 percent of grower/finisher pigs 

tested positive for Toxoplasma antibodies in 2006. 

The percentage of positive samples by herd size is 

shown in figure 1. Small sites had a higher 

percentage of samples positive for Toxoplasma

than medium and large sites, and medium sites had 

a higher percentage of positive samples than large 

sites. 

Facility type was related to percentage of 

grower/finisher pigs that tested positive for

Toxoplasma antibodies. A lower percentage of 

grower/finisher pigs in total confinement tested 

positive for Toxoplasma antibodies compared with

grower/finisher pigs not confined (figure 2).

No grower/finisher pigs from the South region 

tested positive for Toxoplasma antibodies. For the 

other regions, there was little difference in the 

percentage of grower/finisher pigs that tested 

positive for Toxoplasma antibodies (figure 3).

Toxoplasma prevalence—herd-level

A site was classified as positive if it had at least 

one grower/finisher pig test positive for Toxoplasma 

antibodies. Overall, 21.6 percent of sites were 

positive in 2006. A higher percentage of small sites

were positive compared with medium sites and 

large sites. The average within-herd prevalence in 

positive sites was 12.5 percent but ranged from 2.9 

to 62.9 percent.
United States Department of Agriculture • Animal and Plant Health Inspection Service • Safeguarding American Agriculture

Sites that housed grower/finisher pigs in total 

confinement were less likely to be positive than 

sites that did not (figure 5).

For the North, West Central, and East Central 

regions, there was no substantial difference in the 

percentage of positive sites. The South region had 

no positive sites (figure 6).

Conclusions

Site size and facility type appear to impact the 

percentage of pigs and sites positive for 

Toxoplasma antibodies. Small sites may lack 

sufficient controls to prevent exposure of pigs to 

Toxoplasma oocysts from various sources,

including cats and rodents. The prevalence of 

Trichinella in U.S. swine is extremely low.

References 

1 Centers for Disease Control and Prevention, 

Division of Parasitic Diseases. Toxoplasmosis.

Available at: www.dpd.cdc.gov

2 Centers for Disease Control and Prevention. 

Toxoplasmosis Fact Sheet. Available at: 

www.cdc.gov

________________________________

For more information, contact:

USDA–APHIS–VS–CEAH

NRRC Building B, M.S. 2E7

2150 Centre Avenue 

Fort Collins, CO 80526-8117 

970.494.7000

Email: NAHMS@aphis.usda.gov

http://nahms.aphis.usda.gov

#593.0611

____________________________________

The U.S. Department of Agriculture (USDA) prohibits 

discrimination in all its programs and activities on the basis of 

race, color, national origin, age, disability, and where 

applicable, sex, marital status, familial status, parental status, 

religion, sexual orientation, genetic information, political beliefs, 

reprisal, or because all or part of an individual’s income is 

derived from any public assistance program. (Not all 

prohibited bases apply to all programs.) Persons with 

disabilities who require alternative means for communication of 

program information (Braille, large print, audiotape, etc.) 

should contact USDA’s TARGET Center at (202) 720–2600 

(voice and TDD). To file a complaint of discrimination, write to 

USDA, Director, Office of Civil Rights, 1400 Independence 

Avenue, S.W., Washington, D.C. 20250–9410, or call (800) 

795–3272 (voice) or (202) 720–6382 (TDD). USDA is an equal 

opportunity provider and employer.