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Radford G. Davis, DVM, MPH, DACVPM, is an associate professor at Iowa State University. Dr. Davis earned his DVM from Colorado State University and his MPH from University of Arizona. He works to improve global health through building and enhancing animal and public health programs in developing countries in sub-Saharan Africa.
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Toxoplasma gondii is a zoonotic disease with notable significance to pregnant women. This quiz reviews important facts about the disease, its transmission, and its relevance to human health.
A pregnant client brings her 4-year-old neutered cat for vaccinations and routine checkup. She mentions that her physician recommended that she find another home for her indoor/outdoor cat because of the high-risk associated with contracting Toxoplasma gondii infection from cats that are allowed to freely roam.
How do cats most commonly become infected with T gondii?
In utero
By eating other animals
While nursing as kittens
By ingesting the feces of other animals
Via tick bites
Congenital transmission in cats has been documented (and demonstrated experimentally) but appears to be an uncommon route of infection.2-4
Most cats are infected after eating small animals (ie, mammals, birds), which can harbor tissue cysts.5,6
T gondii has been documented in the milk of many species, including cats, but does not appear to be the most common route of infection.5,7
Most cats are infected after eating small animals (ie, mammals, birds) that can harbor tissues cysts, not by eating animal feces.5,6
Although ticks can become infected with T gondii, the role of ticks in infecting cats is unknown and may result from the ticks feeding on infected animals.5
The veterinarian tells the client that cats, as the definitive host for T gondii, will shed oocysts in their feces, thereby contaminating humans, other animals, and the environment. The client asks how long a cat can shed oocysts.
Which of the following statements best describes the duration of shedding of T gondii oocysts by cats?
Most cats rarely shed oocysts when first infected.
Cats typically shed oocysts for just 2 to 3 days after their first infection, which typically occurs early in life.
Cats shed oocysts for up to 3 weeks after their first infection.
Cats shed oocysts for up to 90 days after their first infection.
Cats will shed oocysts on and off throughout their life.
Cats will shed T gondii oocysts for 1 to 2 weeks (up to 3 weeks, median 8 days).5,8
Cats will shed T gondii oocysts for 1 to 2 weeks (up to 3 weeks, median 8 days).5,8
Cats will shed T gondii oocysts for 1 to 2 weeks (up to 3 weeks, median 8 days).5,8
Cats will shed T gondii oocysts for 1 to 2 weeks (up to 3 weeks, median 8 days).5,8
Cats will shed T gondii oocysts for 1 to 2 weeks (up to 3 weeks, median 8 days).5,8
Reshedding of oocysts later in life is possible but rare.8-10
Once T gondii oocysts sporulate, they become infective and environmentally resistant and survive best in humid, warm environments out of direct sunlight.5
Although sporulation is temperature dependent, typically what is the minimum time that T gondii oocysts need to sporulate?
6 hours
12 hours
24 hours
3 days
7 days
Oocysts need 1 to 5 days to sporulate but 1 day at a minimum.5,8,11
Oocysts need 1 to 5 days to sporulate but 1 day at a minimum.5,8,11
Oocysts need 1 to 5 days to sporulate but 1 day at a minimum.5,8,11
Oocysts need 1 to 5 days to sporulate but 1 day at a minimum.5,8,11
Oocysts need 1 to 5 days to sporulate but 1 day at a minimum.5,8,11
A client is concerned about acquiring T gondii infection directly from her cat. The veterinarian explains that because cats only shed oocysts for up to 3 weeks after infection (usually early in life), rarely have diarrhea when infected, and regularly groom themselves, contracting oocysts directly from cat fur is an unlikely means of acquiring infection.5,10 The veterinarian also mentions that there are more common sources of infection for humans.
Which of the following is not a source by which humans can acquire T gondii?
Meat
Vegetables
Soil
Water
Shellfish
None of the above
Undercooked or raw meat plays a significant role in human infection (notably pork, lamb, wild game, goat; beef and chicken to lesser extent).5,8,12-14
Unwashed, uncooked vegetables contaminated with oocysts are a source of human infection.14,16,19,20
Soil is a recognized source and risk for human infection.5,8,12-14 Oocysts can survive in soil for many months to more than 1 year.5,15
Water contaminated with oocysts is a recognized source of infection.4,8,14-16 Outbreaks connected to contaminated water have been documented.17
The risk for infection from eating oysters, mussels, and clams has been documented.5,13,18 Infection in wild mollusks has also been documented.12
Meat, vegetables, water, shellfish, and soil are all sources from which humans can acquire T gondii infection. Humans can become infected by soil and water contaminated with oocysts, undercooked or raw meat, and shellfish (eg, mussels, clams, oysters).5,8,11-18
The veterinarian informs the client that because her cat goes outdoors, it likely has already been exposed to T gondii and become infected.
What is the estimated overall seroprevalence of T gondii infection in cats in the United States (as measured by being seropositive to immunoglobulin M [IgM], IgG, or both antibodies)?
1%
11%
25%
31%
69%
Approximately 31% of all cats in the United States are infected with T gondii as measured by IgM, IgG, or both antibodies. This varies by gender, geographic region, and age.9
Approximately 31% of all cats in the United States are infected with T gondii as measured by IgM, IgG, or both antibodies. This varies by gender, geographic region, and age.9
Approximately 31% of all cats in the United States are infected with T gondii as measured by IgM, IgG, or both antibodies. This varies by gender, geographic region, and age.9
Approximately 31% of all cats in the United States are infected with T gondii as measured by IgM, IgG, or both antibodies. This varies by gender, geographic region, and age.9
Approximately 31% of all cats in the United States are infected with T gondii as measured by IgM, IgG, or both antibodies. This varies by gender, geographic region, and age.9
The client asks whether her cat can be tested for T gondii infection to determine the risk associated with a human contracting the infection.
Which of the following tests is best for determining whether a cat is infectious to humans?
Serology to look for IgM antibodies
Serology to look for IgG antibodies
Serology to look for both IgM and IgG antibodies
Fecal examination to look for oocysts
Polymerase chain reaction (PCR) of feces
A positive IgM titer would indicate a recent infection but may not correlate to active shedding of oocysts. Rarely, some infected cats may fail to mount a detectable IgM response.5,9
If the IgG titer is positive, exposure occurred a long time ago and the cat is highly unlikely to be shedding oocysts; therefore, the risk associated with human health is very low.5,9
A positive IgM titer and negative IgG titer would indicate recent infection but may not correlate to active shedding of oocysts. If only the IgG titer is positive, exposure occurred a long time ago and the cat is highly unlikely to be shedding oocysts; therefore, the risk associated with human health is very low.5,9
Cats are the definitive host of T gondii and therefore shed oocysts4,5,14,19; however, studies have reported that only about 1% of all cats are shedding oocysts at any given time, so finding T gondii infection on a fecal examination can be challenging.5,15 Most cats acquire infection early in life. Only if the cat is shedding oocysts is there a risk associated with humans acquiring infection from direct contact with the cat’s feces or its environment.
PCR is used in molecular research and to diagnose infection in cats or humans with clinical disease or at postmortem.4,14 It is not routinely used to detect oocysts in feces.
During their conversation it becomes clear that the client has not been tested for T gondii infection, the veterinarian thusly recommends that the client see her physician.
Which of the following statements about pregnancy, T gondii infection, and risk for the fetus is most accurate?
A woman who is infected with T gondii before becoming pregnant generally has immunity that usually protects the fetus against infection.
A woman who is serologically negative for T gondii poses little to no risk for infecting the fetus during pregnancy, as she is not infected.
A woman who is not yet pregnant but is serologically positive for T gondii is at high risk for infecting the fetus during pregnancy.
Only pregnant women exhibiting clinical signs of T gondii infection during pregnancy pose a risk for their fetus.
All of the above are accurate.
With rare exceptions of infection occurring shortly before conception, if a pregnant woman contracts T gondii infection before pregnancy, she has immunity that prevents against passing that infection to the fetus.14,19,20
Because the woman is not infected and has no immunity to T gondii, she is at risk for acquiring infection during pregnancy and thus infecting the fetus.14,20
Mother-to-fetus transmission of T gondii infection is limited almost exclusively to women who acquire the infection during pregnancy. If a woman is serologically positive before conception, there is little to no risk for infecting the fetus.14,20
Only about 10% to 20% of immunocompetent humans, including pregnant women, exhibit clinical signs when infected with T gondii.14 Therefore, a woman could be infected during pregnancy, not exhibit signs, and still infect the fetus.
With rare exceptions of infection occurring shortly before conception, pregnant women who contract T gondii infection before pregnancy have immunity that prevents them from passing the infection to the fetus. Mother-to-fetus transmission of T gondii is limited almost exclusively to women who acquired the infection during pregnancy.14,19,20
Given what the veterinarian has told the client about the prevalence of T gondii infection in cats in the United States, the client is curious about how common T gondii infection is in the US human population.
Based on CDC data, what is the estimated percentage of the US population 12 years of age or older that has been exposed to T gondii (based on serologic testing)?
≈1%
≈12%
≈22%
≈43%
≈85%
The CDC estimates that approximately 22.5% of US residents 12 years of age and older have been exposed to T gondii.21
The CDC estimates that approximately 22.5% of US residents 12 years of age and older have been exposed to T gondii.21
The CDC estimates that approximately 22.5% of US residents 12 years of age and older have been exposed to T gondii.21
The CDC estimates that approximately 22.5% of US residents 12 years of age and older have been exposed to T gondii.21
The CDC estimates that approximately 22.5% of US residents 12 years of age and older have been exposed to T gondii.21
After discussing and reviewing all available information on T gondii infection, the veterinarian and client agree on recommendations for best avoiding the risks for infection.
Which of the following is NOT recommended to help prevent T gondii infection in pregnant clients?
Remove the cat from the home.
Keep the cat indoors.
Have someone else scoop or change the litter box daily; if a pregnant client must do it, she should wear gloves and wash her hands well afterward.
Wear gloves when doing yard work or gardening to avoid soiling the hands; wash hands immediately afterward.
Cook meat well and peel or wash fruits and vegetables before consumption.
This recommendation would not appear on the list. The CDC supports having pregnant women keep their cats.25 Contracting oocysts directly from cats is an unlikely route of infection.5,6,10 Some studies have demonstrated association between human infection and owning cats,13,18,22 whereas other have not.23,24
This action is recommended by the CDC. When a cat is outdoors, it can contract T gondii infection by eating intermediate hosts (eg, small rodents).24,25 The cat would then shed oocysts, putting the owner at risk for infection. This client’s cat probably is already infected with T gondii since it is older and has spent time outdoors.
Daily scooping or changing of the litter box is recommended by the CDC25 to dispose of any oocysts before they sporulate and become infectious, and environmentally resistant.
Wearing gloves and washing hands are recommended by the CDC25 to help prevent hand-to-mouth transmission of oocysts harbored in soil.
These measures are recommended by the CDC to reduce the likelihood of infection.25
Quiz: <em>Toxoplasma gondii</em> & Pregnancy
Final scoreReferences and Author Information
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Atmaca HT, Dincel GC, Macun HC, et al. A rare case of feline congenital Toxoplasma gondii infection: fatal outcome of systemic toxoplasmosis for the mother and its kitten. Berl Munch Tierarztl Wochenschr. 2013;126(5-6):216-219.
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Pereira LH, Staudt M, Tanner CE, Embil JA. Exposure to Toxoplasma gondii and cat ownership in Nova Scotia. Pediatrics. 1992;89(6 Pt 2):1169-1172.
Minbaeva G, Schweiger A, Bodosheva A, et al. Toxoplasma gondii infection in Kyrgyzstan: seroprevalence, risk factor analysis, and estimate of congenital and AIDS-related toxoplasmosis. PLoS Negl Trop Dis. 2013;7(2):e2043.
Wallace MR, Rossetti RJ, Olson PE. Cats and toxoplasmosis risk in HIV-infected adults. JAMA. 1993;269(1):76-77.
Centers for Disease Control and Prevention (CDC). Toxoplasmosis and pregnancy—FAQ. http://www.cdc.gov/parasites/toxoplasmosis/gen_info/pregnant.html. Accessed Feb 1, 2106.
Pappas G, Roussos N, Falagas ME. Toxoplasmosis snapshots: global status of Toxoplasma gondii seroprevalence and implications for pregnancy and congenital toxoplasmosis. Int J Parasitol. 2009;39(12):1385-1394.
Author Information
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