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It is estimated that 500 million people worldwide are infected with Toxoplasma
gondii.1 Seroprevalence studies have uniformly
indicated increasing rates with age (eFig. 354.1). Between 1999
and 2004, the age-adjusted T. gondii seroprevalence
rate declined from 14.1% to 9% among U.S.-born persons
ages 12 to 49 years.2 The rates varied among regions, probably
due to differing climates, culinary practices, and immigration patterns
from areas of the world that have higher endemic rates of Toxoplasma infections. Data
from Europe generally indicates a slightly higher prevalence rate
compared to the United States, with rates in Central Europe ranging
from 24% in Greece to 41% in France and Poland.3-5 In
the United States, seroprevalence rates in women of childbearing
age are approximately 15%, whereas rates in similar populations
from western Europe, Africa, and Central and South America are greater
than 50%.1,6 The general population of blood donors
from Turkey was found to have a 20% seroprevalence rate, while
the seroprevalence restricted to women was found to be relatively
high at 52.1%.7,8 In the last two decades, most
European countries have noted a decrease in seroprevalence of Toxoplasma,
possibly due to less infection in farm animals, more filtration
of drinking water, and concerns about consuming undercooked meat.
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Seroprevalence rates in India, Sudan, Uganda, and Malaysia range
from 20% to 55% in recent studies.9-12 In
New Zealand, 33% of women who had antenatal blood work were
found to have antibodies to T gondii, indicating
past infection.13 Seroprevalence in Brazil was estimated
to be between 40% to 80%.14 Globally,
infection rates primarily reflect soil temperatures—infection
is much more common in warmer or temperate climates and is much
less common in colder climates, such as in the northern hemispheres.
Specific populations at risk included butchers and individuals of
lower socioeconomic status.15,16 A study of children in
a low-socioeconomic community in Brazil found a seroprevalence rate
of 32.4%.17
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T. gondii is a parasite for which the members
of the feline species (ie, cats, kittens, cougars) are the definitive hosts.18 Felines
ingest the cyst form that is present in soil, which germinates in
the cat’s small intestine and produces oocysts. The oocysts
are then excreted in the feces for a period of 7 to 20 days into
the surrounding environment. The oocyst can sporulate and become
infective in the proper environmental conditions (such as warm soil). The
oocyst does not sporulate below 4°C, which explains why colder climates
would be inhospitable to sporulation. It is the sporulated oocyst
that is infective when ...