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Toxoplasma gondii

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Toxoplasma gondii is a protozoal parasite capable of infecting any warm-blooded animal, including humans. Wild and domestic cats are the only known definitive hosts of Toxoplasma; they can develop both systemic and patent intestinal infection. All other animals and humans serve as intermediate hosts in which the parasite may cause only systemic infection, which typically results in the formation of tissue cysts. Wild and domestic cats are the only known definitive hosts of Toxoplasma; they can develop both systemic and patent intestinal infection. All other animals and humans serve as intermediate hosts in which the parasite may cause only systemic infection, which typically results in the formation of tissue cysts. For Vets In all species, Toxoplasma infection is usually subclinical, although it may occasionally cause mild, non-specific signs. Infection may have much more serious consequences in immunocompromised or pregnant animals and people. In all species, Toxoplasma infection is usually subclinical, although it may occasionally cause mild, non-specific signs. Infection may have much more serious consequences in immunocompromised or pregnant animals and people. The major modes of transmission include consumption of undercooked meat containing Toxoplasma cysts, fecal-oral transfer of Toxoplasma oocysts from cat feces (either directly or in contaminated food, water or soil), and vertical transmission from mother to fetus if primary infection occurs during pregnancy. The major modes of transmission include consumption of undercooked meat containing Toxoplasma cysts, fecal-oral transfer of Toxoplasma oocysts from cat feces (either directly or in contaminated food, water or soil), and vertical transmission from mother to fetus if primary infection occurs during pregnancy. The risk of contracting Toxoplasma infection from cleaning the litter box of a house cat is actually very small, especially if a few simple precautions such as appropriate hand washing are observed. The risk of contracting Toxoplasma infection from cleaning the litter box of a house cat is actually very small, especially if a few simple precautions such as appropriate hand washing are o
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General Information

Toxopla
Toxo
s
pla ma gondii
m
is
i a protozoa
a protozo l parasite capable of
l parasite capa
infect
ble of
ing any
infect
warm
ing any
-blo
warm
ode
-blo
d animal, incl
ode
uding h
d animal, incl
uman
uding h
s
uman .
Wild and dom
Wild an
estic
d dom
cat
estic
s
cat are the only kn
are
o
the only kn w
o n definitive host
n definitive
s
host of Toxo
To
plasm
xo
a
plasm ; they can develop
; they can
both sy
develop
stemic and
both sy

stemic and
patent intestinal infection. All other animals and hu
patent intesti
mans
nal infection. All other animals and hu
serve as
serve a intermediat
interme
e hosts in whi
diat
c
e hosts in whi h the paras
h the para ite may
it
caus
cau e on
e o ly systemic infecti
ly systemic infe on, whi
cti
c
on, whi h typically results in the formatio
in the format n of
io
t
n of i
t ssue cy
ssue st
cy s.
st
s.
In all species, Toxoplas
Toxopla m
s a
m infection is usually subclini
infection is usually su
c
bclini al, although it may occa
al, alth
sion
ough it may occa
ally
sion
caus
cau e mild, non-specifi
e mild, non-sp
c
ecifi signs. Infection
sign
may have much more seriou
may have much more seri s con
ou
s
s con eque
s
nces in
eque

nces in
immunocom
immuno
p
com romi
p
sed o
romi
r
sed o pregnant anima
pregna
ls and p
nt anima
eopl
ls and p
e
eopl .
e
.
The major m
The majo
ode
r m
s of tran
ode
smissio
s of tran
n in
smissio
cl
n in ude
cl
cons
con umption of und
um
ercoo
ption of und
k
ercoo ed me
ed m at containi
e
ng
at containi
Toxopla
Toxo
s
pla ma
m cyst
cy s,
st f
s, e
f cal-o
cal ral t
-o
ran
ral t
sf
ran er of
sf

er of Toxopla

s
Toxopla ma
m ooc
a
ysts from cat feces (either directly
t
or in contaminated food, water or soil),
or in contami
and vertical transmission from mother to
and vertical transmi

ssion from mother to
fetus if primar
fetus if prima y infection occurs du
r
rin
y infection occurs du g
rin pregnancy.
pregna
The risk of contracting
of contra
To
T xopl
o
asm
xopl
a
asm infe
inf ction fr
ction f om cleanin
om
g
cleanin the litter box of a
the li

tter box of a
house cat is
hou
actually very small, espe
se cat is
ci
actually very small, espe a
ci lly if a few simple pre
few si
c
mple pre autions
a
su
utions ch as
su
appropriate h
approp
and washing
riate h
are ob
and washing
se
are ob rved.
se

rved.

Prevalence of Tox
Prevalence of
opl
Tox
asm
opl
a
asm
Toxopla
Toxo
s
pla ma
m is on
a
e of the
is on

e of the most

wide
most
sp
wide read
sp
zoo
read
notic
zoo
pathog
notic
en
pathog s in
en
the wo

rld. In
the wo
most a
rld. In
nimal
most a
s an
nimal
d p
s an
eople,
d p
prima
eople,
r
prima y
y
infection re
infection sults in a
re
det
sults in a
ectabl
det
e antib
ectabl
ody titre for
e antib
the lif
ody titre for
e of the ho
the lif
st, there
e of the ho
f
st, there ore
f
se
ore roprev
ropre alence (i.e.
v
previou
alence (i.e.
s
previou
s
exposure to the parasite bu
exposure to the parasite b t not necessarily
t not nece
clinical disease) increases
e with age.

Humans

Hum
Becaus
Becau e toxopla
e tox
s
opla mosis i
mo
s
sis i not a repo
not a re rtable di
po
sea
rtable di
s
sea e in On
s
tario and mo
tari
st of North Am
o and mo
eri
st of North Am c
eri a, it is difficult to
c

estimate the
estimate th prevale
e
n
prevale ce of infection i
ce of
n
infection i an
a imals or pe
imals or ople. An aver
ople. An ave age 15
age
000
15
ca
000 se
ca s of
se
clini
s of
c
clini al toxoplasmosi
al toxopl
s
asmosi
are repo
are
rted
repo
annu
rted
ally in the USA, but it
annu
has b
ally in the USA, but it
een
has b
estimated that the a
een
c
estimated that the a tual number
tual nu
of ca
mber
se
of ca s is li
se
kely cl
s is li
o
kely cl s
o er to
er t
o
225 000. It is
225 00
estimated that 50% of these cases o
estimated th
ccur due to foo
at 50% of these cases o
dborne tra
ccur due to foo
n
dborne tra smission of
smissi
Toxopl
To
asm
xopl
a
asm .
Seropr
Serop evalen
evale c
n e in the gen
e in the ge e
n ral populatio
ral po
n in person
pulatio
s
n in person over 12 yea

r
over 12 yea s of age was estimated to
r
be 22.5% in one
s of age was estimated to
North Ameri
North Am c
eri an study p
c
erf
an study p
orme
erf
d from 1
orme
988-199
d from 1
4. Worl
988-199
d
4. Worl w
d ide, seropreval
ide,
en
seropreval ce range
en
s from
ce range
0
s from -
0 100% depe
100% d
n
epe ding
n
on country, geographi
on co
c a
untry, geographi
r
c a ea and even et
e
hnic g
a and even et
r
hnic g oup.
ou
Between 40
Between 4 to 400 children born in
to 400 childre
Can
n born in
ada ea
Can
ch yea
ada ea
r
ch yea are infected
are infe
with
cted
Toxopla
To
s
xopla m
s a
m before birth.

Animals
The pr
The p evalen
evale c
n e of oo
e of cyst
oo
she
cyst
ddin
she
g
ddin in cats i
in
s
cats i very low (0-1%
very lo
)
w (0-1% , even thou
, ev
gh
en thou
se
gh rologi
se
cal
rologi
stu
cal
d
stu i
d es indicate t
es in
hat at
dicate t
least 15-40%
least 15
of cats have
-40%
been infe
of cats have
cted
been infe
, dependi
cted
ng o
, dependi
n
ng o how the cat
the
s
cat are fed and
are fe
wheth
d and
e
wheth r they go outdoors.
r they go outdo
Diseas
Disea e and exposure a
e an
r
d exposure a e more
e
comm
more
o
comm n in cats a
o
nd
n in cats a
other pet
nd
s tha
other pet
t
s tha go outdoors,
t
hunt, or are f
go outdoors,
ed ra
hunt, or are f
w meat.
ed ra

Zoonotic Risk & Other Ris
Zoonotic Risk & Ot
k
her Ris Factors
Fa
The risk of transmission o
The risk of transmi
f
ssion o
f Toxoplas
Toxopla ma
m from a household cat can be easily controlled by
from a househ
means of simple
old cat can be easily controlled by

means of simple
infectious
infectiou disease co
di
ntrol
sease co
pro
ntrol
c
pro edures
ed
(see Infe
ures
ction
(see Infe
Cont
ction
rol below
rol belo ). In one study from Norway, clea
). In one
ning
study from Norway, clea
a cat
ning

a cat
litter box was found to be
litter box was found to
a strong
be
ri
a strong sk factor fo
ri
r ex
sk factor fo
posure
r ex
to
posure
Toxopl
To
asm
xopl
a
asm . However, th
,
e s
ame stud
t y, and
another Euro
anothe
pean
r Euro
study, showed
pean
no a
study, showed
s
no a so
s ciation b
so
etwee
ciation b
n
etwee Toxoplasm
Toxopl
a
asm exposur
exposu e and living with or ne
e and living
ar a
with or ne
cat.
ar a
Contaminatio
Contami
n of water source
natio
s and
n of water source
soil with the
s and
feces of wil
soil with the
d or
feces of wil

domes
dome tic cats
tic cat is more diff
is more dif icult to control, and can lead to infection
f

icult to control, and can lead to infection
following
followin inge
ing stion of oocysts on
stion of oo
unwa
un
she
wa
d
she , uncooked vegetable
, uncoo
s
ked vegetable or
in contam
in conta inated wate
inat
r. Cockro
ed wate
ache
r. Cockro
s a
ache
nd co
s a
proph
nd co
a
proph gic flies m
a
ay also
gic flies m

ay also
serve a
serv
s
e a mech

ani
mech
cal
ani
v
cal
e
v ctors
ct
of
ors
of
Toxoplasm
Toxopl
a
asm , resulting in
contaminatio
contami
n of food, water or ut
natio
en
e sils
sil with infec

tiou
tio s
u oocysts.
oo
Contac
Conta t with conta
t with
m
conta inated soil
inate
or
d soil
san
or
d, su
san
ch a
d, su
s
ch a in a ga
i
rde
n a ga
n
rde or
n
a
or
a
sandbox, is al
san
so be a
dbox, is al
s
so be a so
s cia
so
t
cia ed with
t
Toxo
To
plasm
xo
a
plasm infection.
t
Cons
Con umption
um
of undercoo
ption
k
of undercoo ed meat is
ed me
one of the prin
one of the pri ciple risk factors
cipl
for Toxoplas
Toxopla m
s a
m infection, and people
infection, and peo
who h
ple
andl
who h
e raw me
andl
at (su
e raw me
c
at (su h as
h a
s
abattoir workers) may also be more co
abattoir workers) may also
mmonly expo
be more co
sed to the pa
mmonly expo
rasite.
sed to the pa

rasite.
The importan
The imp
ce of the
ortan
s
ce of the e variou
e v
s
ariou ri
s sk fa
ri
ctors likely varies
sk fa
co
ctors likely varies nsi
co
derably
nsi

derably
between ethn
betwe
ic group
en ethn
s du
ic group
e to differen
s du
c
e to differen es in
c
cultural
es in
habits rega
cultural
rding
habits rega

rding
exposure to underco
exposure to u
oked
nderco
meat, soil an
oked
d cats.
meat, soil an
www.wormsandgermsblog.com Updated June 3, 2008


Life Cycle of Toxoplasma
Unsporulated oocysts of Toxoplasma are passed in
the feces of acutely infected cats. The oocysts usually Bradyzoites
Bradyzoites
sporulate in 1-5 days forming two sporocysts, each in tissue cyst
in tissue cyst
containing four infective sporozoites. When the
oocysts are ingested by any warm-blooded host, the
sporozoites excyst, invade intestinal cells and begin to
divide asexually to produce tachyzoites. These then
migrate throughout the body, invading tissue cells and
multiplying until the cells rupture. Eventually the
Sporulated
tachyzoites encyst, becoming bradyzoites, within cells
oocysts
of the central nervous system, muscle, and sometimes
other organs. The cysts typically persist until death of
the host without causing clinical signs. If the host is
eaten by another animal, the bradyzoites excyst in the
intestine and the process is repeated,
forming new tissue cysts.

If an intermediate host is eaten by a cat,
Bradyzoites
in tissue cyst
the bradyzoites invade the intestinal
Tachyzoites
during pregnancy
epithelial cells and undergo five stages of
asexual reproduction (merogeny) followed by formation of microgamonts and macrogamonts. The microgamonts
divide to form flagellated microgametes, which then fertilize the macrogamonts. The fertilized macrogamont forms
a wall and becomes an unsporulated oocyst approximately 10 ?m x 12 ?m in size, which is passed in the feces of
the cat. When fed tissue cysts, 97% of cats infected for the first time will produce oocysts, usually within 3-10 days.
They may shed for up to 20 days, but the majority of oocysts will be shed in just 1-2 days. Only 20% of cats fed
oocysts will develop a patent infection, and the prepatent period may be 18 days or more. Contrary to previous
beliefs, studies have shown that oocysts can be shed in low numbers by previously infected cats that are
challenged again with the parasite or that become immunosuppressed due to disease or drug therapy.

Transmission of Toxoplasma
Carnivorous animals are often infected with Toxoplasma through ingestion of bradyzoites from tissue cysts in
infected prey, as are people who eat undercooked meat, particularly that of pigs, sheep and goats. Toxoplasma
cysts are less commonly found in poultry and rarely found in beef. The prevalence of Toxoplasma infection in
commercial farm animals has decreased significantly with the advent of intensive management practices. Free-
range poultry, swine and small ruminants, marsupials (e.g. kangaroos) and some wild game are more likely to
harbour cysts.

Oocysts are only shed by cats. Unsporulated oocysts in fresh feces are not infective; they need appropriate
oxygen, humidity and temperature to sporulate. Sporulated oocysts are the most environmentally resistant life
stage of the parasite. Ingestion of as few as ten oocysts may infect an intermediate host, while ingestion of 100 or
more oocysts can cause a patent infection in a cat, which may shed tens to hundreds of millions of oocysts.
Sporulated oocysts from cat feces can survive passage through the intestine of a dog.

Tachyzoites are potentially infective, and may be found in the tissues of acutely infected animals, as well as the
milk of sheep, goats, cows, and sometimes chicken eggs. However, tachyzoites are killed relatively easily by
pasteurization, and uncommonly survive gastric digestion, although this may be more of a concern in infants who
have lower concentrations of peptic enzymes. Any kind of cooking will kill tachyzoites in an egg. Toxoplasma can
also be transmitted by organ transplants and blood transfusions, but this is uncommon.

In utero transmission of Toxoplasma occurs only if primary infection of the dam/mother occurs during pregnancy.
Parasitemia then results in placentitis and infection of the fetus. This is more likely to occur in humans, sheep and
goats, and sometimes mice, cats and dogs. Kittens can be infected transplacentally or through tachyzoites shed in
the queen’s milk. Under normal circumstances, a female that has been exposed to Toxoplasma 4-6 months prior to
pregnancy will develop sufficient immunity to protect herself and the fetus for the rest of her life. However, if the
immune response is suppressed by drug therapy or disease such as HIV/AIDS in humans, both the mother and the
fetus may become susceptible to infection again. In humans, the risk of the infection being passed on to the fetus
increases from the first trimester (10-25%) to the third trimester (60-90%). However, the potential congenital
defects are more severe with earlier infections.
www.wormsandgermsblog.com Updated June 3, 2008


Symptoms and Signs
Clinical signs of toxoplasmosis are caused by cellular destruction due to multiplying tachyzoites, which most
commonly affect the brain, liver, lungs, skeletal muscle and eyes. Infection may be associated with other diseases
such as distempter or ehrlichiosis in dogs, hemobartonellosis, feline immunodeficiency virus (FIV) infection in cats,
or immunosuppressive therapy in any species.

Humans: Approximately 15% of cases of Toxoplasma infections are associated with clinical signs such as mild
fever and lymphadenopathy. Signs may persist for 1 to 12 weeks; more severe disease is very rare in
immunocompetent individuals. Of clinical cases, 0.2%-0.7% may develop ocular toxoplasmosis (retinitis), but this
is more commonly associated with congenital infection. If more severe disease develops, signs may be related to
encephalitis, hepatitis, myositis or pneumonia. Toxoplasma encephalitis develops at some time in approximately
40% of individuals with AIDS, and is fatal in 10-30% of these cases.

Approximately 10% of congenital Toxoplasma infections result in abortion or neonatal death. In 10-23% of
congenital infections, signs are present at birth; these may include hydrocephalus, chorioretinitis, microcephally and
small size. Clinical signs are not apparent at first in 67-80% of cases. Ocular toxoplasmosis may occur in up to 1/3
of children that survive congenital infection.

Animals:
In healthy, naïve cats, primary infection with Toxoplasma is typically either subclinical or may cause mild small-
intestinal diarrhea for up to 10 days. In rare cases when cats develop significant clinical disease, signs may
include fever, lethargy, anorexia, and others associated with pneumonia, hepatitis, myositis or encephalitis.
Pancreatic, cardiac and ocular tissues are also commonly affected. Dermatitis and vomiting have also been
reported. The onset of signs may be slow, or the disease may be rapidly fatal. Neurologic and ocular signs
without systemic illness are more common with reactivated infections.
Congenitally or lactationally infected kittens are often severely affected due to
uncontrolled replication of tachyzoites and tissue damage. Kittens may be
stillborn or die before weaning, typically with signs related to pneumonia,
hepatitis or encephalitis. However, in some cases the only sign of disease may
be chorioretinitis, and occasionally concurrent anterior uveitis.
Clinical signs and tissue involvement are similar in dogs, but ocular lesions are
much less common. Generalized toxoplasmosis typically occurs in dogs less
than one year old. Clinical signs in older dogs are primarily associated with
encephalitis and myositis, and appear very similar to Neospora caninum
infection.

Clinical infection in sheep and goats is much more common than in dogs and cats, and is primarily associated with
reproductive problems, including abortion and birth of weak young that are incoordinated and unable to feed
themselves. The infection can also be common in birds, but it is rarely clinical.

Diagnosis
Once infected with Toxoplasma, people and animals usually develop a life-long protective antibody titre, unless the
individual is severely immunocompromised and unable to mount or sustain an appropriate humoral immune
response. The organism itself can be detected in tissues or body fluids using either PCR or bioassays in mice.

Infection in Humans: There are several different serological tests used to diagnose
toxoplasmosis in humans that are intended to help differentiate between latent and
acute infections. Serum IgM titers indicate recent infection, whereas serum IgG
titers persist longer and therefore typically indicate previous infection. However, both
types of antibodies are usually detectable within 1-2 weeks of infection. Some
Toxoplasma IgM test kits have relatively high false-positive rates. Measurement of
IgG avidity can also help “age” the antibody response. The modified latex
agglutination test (MAT) detects IgG, but can help differentiate acute and chronic
infections based on reactivity with acetone versus formalin-fixed antigen. It is
considered extremely sensitive.

Serological screening of pregnant women is not generally recommended in the USA and Canada as it is in some
European countries, because the risk of exposure to Toxoplasma is comparatively low. Diagnosis of in utero
infection is most commonly accomplished by detecting Toxoplasma DNA in amniotic fluid using PCR.
www.wormsandgermsblog.com Updated June 3, 2008



Clinical Infection in Animals
: Both leukopenia and leukocytosis may be observed in animals with clinical
toxoplasmosis. Serum biochemistry abnormalities are related to the primary tissues involved (e.g. liver, muscle,
pancreas). In acute infection, tachyzoites may be rarely seen in peripheral blood, cerebrospinal fluid (CSF), or lung
or tracheal wash fluid, but are more commonly found in thoracic or abdominal effusions. Changes in the CSF of
encephalitic cats are inconsistent, but may include increased protein and lymphocytic or mixed inflammatory cells.

A diagnosis of clinical toxoplasmosis is difficult to make antemortem in animals, and should be made based on a
four-fold or greater change in antibody titre or a single high IgM titre, response to anti-Toxoplasma therapy, and
exclusion of other differential diagnoses. Toxoplasma-specific antibody may also be detected in the aqueous
humor or CSF of cats with ocular or neurologic signs, respectively, but the titre must be compared to that of a non-
ocular or non-neurologic pathogen to determine if the antibody was produced locally.

Subclinical Infection in Cats: It is important to note that the development
and persistence of IgM in infected cats is very inconsistent, and is not a
reliable marker of acute Toxoplasma infection. Furthermore, some cats
may not develop IgG titres until 4-6 weeks after infection, well after they
have stopped shedding oocysts, and the titre may peak in as little as 2-3
weeks and remain high for years.

A cat that is IgG seropositive is unlikely to be shedding oocysts, and
is unlikely to shed oocysts if it is exposed to the parasite.

Nonetheless, exposure should be minimized as some seropositive cats
may shed low numbers of oocysts if re-exposed. A cat that is
seronegative is unlikely to be shedding oocysts, but is likely to
develop a patent infection if it is exposed to Toxoplasma.


Oocyst Shedding in Cats: Cats typically only shed oocysts in their feces for 1-3 weeks following their first
exposure to Toxoplasma, therefore fecal examination is usually unrewarding. If present, the oocysts are best
detected using a centrifugal fecal floatation technique with Sheather’s sugar solution (specific gravity 1.26). The
unsporulated oocysts have no distinct internal structures, and are approximately 10 ?m in diameter (1/4 the size of
Cystoisospora oocysts, and 1/8 the size of Toxocara cati eggs). They are indistinguishable from oocysts of some
species of Hammondia and Besnoitia, which also occur in cats, but these oocysts should be considered
Toxoplasma until proven otherwise.

Treatment of Toxoplasmosis
Animals
:
Clindamycin (dogs 10-20 mg/kg, cats 10-12.5 mg/kg, PO or IM, q12h for 4 weeks) is the drug of choice for
clinical toxoplasmosis in dogs and cats. This dose is higher than that on the product label. High-dose oral
clindamycin therapy can cause anorexia, vomiting and diarrhea in dogs and cats. Improvement should be seen
within 48 hours, but FIV-infected cats in particular may be more difficult to treat.
Cats with ocular inflammation should also be treated with either topical (ideally) or systemic glucocorticoids.
Pyrimethamine (dogs and cats 0.25-0.5 mg/kg, PO q12h for 4 weeks) and a
sulfonamide (dogs and cats 30 mg/kg, PO q12h for 4 weeks) in combination are the
second choice treatment. Cats must be monitored for signs of bone marrow
suppression when this treatment regimen is used for more than 2 weeks. Newer
macrolides (e.g. azithromycin, clarithromycin) may be effective against Toxoplasma,
but are not licensed for use in animals. Doxycycline or minocycline may be used if
there is concurrent infection with a different tetracycline-susceptible pathogen.

Oocyst shedding in cats can be reduced by use of the therapeutic dose of clindamycin,
or high-dose sulfonamide-pyrimethamine combinations (100 mg/kg-2.0 mg/kg, PO
q24h for 1-2 weeks). Monensin (mixed in food as 0.02% w/w dry weight for 1-2 weeks)
or toltrazuril (5-10 mg/kg PO q24h for 2 weeks) can also be used, if given within 1-2
days of exposure or administration of immunosuppressive therapy to the animal
(which may cause recrudescence of infection). An oral vaccine to reduce oocyst
shedding in cats has been developed, but is not currently commercially available.
www.wormsandgermsblog.com Updated June 3, 2008

Infection Control

In the majority of studies, no direct association has been found between cat ownership and the risk of
toxoplasmosis in people.
Given the emotional benefits associated with owning a cat, and the minimal risk of
transmission of Toxoplasma if appropriate hygiene is practiced, even pregnant or immunocompromised individuals
do NOT need to give up their cats. Such individuals should avoid contact with cat feces and cat litter whenever
possible by having someone else clean their cat’s litter box. If a cat is found to be shedding oocysts, it should be
removed from the premises temporarily and treated to eliminate shedding. Because cats are usually meticulous
groomers, it is unlikely that oocysts will be found on their fur, so regular handling is not a significant risk.
Individuals should always wash their hands thoroughly after contact with cat stool, litter or a litter box.

Microwave cooking, salting and smoking do not consistently kill all infective Toxoplasma organisms. Freezing meat
to –12ºC for at least 24 hours will kill most Toxoplasma tissue cysts, but sporulated oocysts can survive at –20ºC
for up to 28 days. Washing kitchen utensils and surfaces that have come in contact with raw meat with soap and
scalding hot water will kill any bradyzoites or tachyzoites present.

Oocysts take longer to sporulate under cooler conditions. At room temperature sporulation may occur within 1-5
days, but this can take 3 weeks at 11ºC. Once sporulated, oocysts can survive even longer in the environment.
They are resistant to most disinfectants, therefore immersion of litter boxes and other potentially contaminated
instruments in boiling or scalding water is the preferred means of decontamination. Even sporulated oocysts are
killed by heating to 55-60ºC for 1-2 minutes. Cat feces should be disposed of daily to reduce the risk of
transmission. Feces and dirty litter can be disposed of in a septic system if the litter is biodegradable, sealed tightly
in a plastic bag and placed in the garbage, or incinerated. Backyard compost units do not produce sufficient heat to
destroy oocysts and other pathogens potentially present in fecal material. Also keep cats out of sandboxes and
other areas where children play that cats may be inclined to defecate.

Zoonotic Disease Risk
The zoonotic risk to the general population posed by Toxoplasma in cats is:

HEALTHY ADULTS

LOW RISK

1 2 3 4
5
6
7
8
9 10 HIGH RISK


Pregnant Women and Individuals with Compromised Immune Systems:
Education of individuals in these high risk groups about how to decrease the transmission of Toxoplasma is an
important tool in the prevention of this disease. Recommendations for preventing toxoplasmosis include:
Cook all meat to a minimum internal temperature of 67ºC/153ºF.
Peel or thoroughly wash fruit and vegetables prior to consumption.
Clean all surfaces and objects that come in contact with raw meat or unwashed fruit and vegetables.
Avoid contact with cat litter and garden soil, otherwise wear gloves and wash hands thoroughly after.
Avoid feeding raw meat to cats.
Keep cats indoors so they do not become infected by eating small prey.

For these groups, the zoonotic risk posed by Toxoplasma in cats is likely:

PREGNANT / IMMUNOCOMPROMISED PERSONS

LOW RISK
HIGH RISK

1 2 3 4
5
6
7
8
9 10


Additional Reading
Greene CE. Infectious Diseases of the Dog and Cat. 3rd ed. Edinburgh: Elsevier Saunders, 2006.
Shuhaiber S, Koren G, Boskovic R, et al. Seroprevalence of Toxoplasma gondii infection among veterinary staff
in Ontario, Canada (2002): Implications for teratogenic risk. BMC Infect Dis. 2003;3:8.
Tenter AM, Heckeroth AR, Weiss LM. Toxoplasma gondii: From animals to humans. Int J Parasitol.
2000;30:1217-1258.
www.wormsandgermsblog.com Updated June 3, 2008

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