Transcript Toxoplasma gondii - Winona State University

Alice Kamau,
Eva Dali,
Amal Mohamed
Kingdom: Alveolata
Phylum: Apicomplexa
Class: Coccidia
Order: Eucoccidiorida
Family: Sarcocystidae
Genus: Toxoplasma
Species: gondii
HISTORY
Tachyzoites (6 x 2 µm
Toxoplasma
gondii is a single
celled parasite
that causes a
disease known as
toxoplasmosis. It
invades muscle
and intestinal
epithelium.
Discovered in
1908 in a desert
rodent called
gondi.
Bradyzoites
Toxoplasma
originated from
the Greek word,
toxon which
means bow.
Toxoplasma
means ‘bow
shaped’ organism.
Definitive host: Domestic cats and their relatives
(Felidae family).
Intermediate host: birds, rodents, cows, sheep, humans
and other mammals.
Geographical range: worldwide. Infection is highest in
hot and humid climates and lower altitudes. In the U.S,
over 60 million people may be infected i.e. 22.5 % of the
population. Toxoplasma gondii is transmitted by three
known modes: congenitally, through the consumption of
uncooked infected meat and via fecal matter.
•The parasite has two life cycles: Direct and Indirect
LIFE STAGES

Infectious:
Tachyzoites - Rapidly multiplying form
 Bradyziotes - In infected tissue
 Oocysts – Shed in feces


Division:
Sexual stages are produced only in the feline
definitive hosts (cats).
 Asexual stages occur in any of the prospective warm
blooded animals (birds, dogs, pigs, cattle, humans,
etc.).

LIFE CYCLE WITHIN THE INTESTINE
•The infection is acquired through the ingestion of sporulated
oocysts (Oo).
• Sporozoites (Sz) are release in the intestinal lumen and invade
intestinal epithelial cells.
• Within the epithelial cells the parasite undergoes a round of
merogony/schizogony leading to the production of merozoites (Mz).
• The released merozoites reinvade intestinal epithelial cells and
can undergo additional rounds of merogony or develop into either
micro- or macrogamonts.
• Microgametes (ga) will fertilize the macrogametes (ga) to form a
zygote (Zy) which develops into the oocyst (Oo).
• Immature oocysts are passed in the feces and maturation into
infectious sporulated oocysts occurs in the environment.
• Recognizable stages during this maturation (ie, sporogony) include
oocysts with a single sporoblast, oocysts with two sporoblasts, and
the mature oocyst with two sporocysts, each of which contains four
sporozoites.
IN THE INTESTINES OF A DEFINITIVE HOST
Sz-Sporozoites
 Mz-Merozoites
 Ga-gametes
 Zy-Zygote
 Oo-Oocyte
 Bradyzoites released
in the intestine,
infects cells forming
trophozoites and
undergo asexual
production called
schizogony

1. Oocysts are shed in the cat's feces.
o Large numbers are shed, but usually only for 1–2 wk.
Oocysts take 1–5 days to become infective.
o Cats become reinfected by ingesting sporulated
oocysts.
2. Soil, water, plant material, or cat litter become
contaminated with oocysts.
oIntermediate hosts in nature (eg, birds, rodents, wild
game, animals bred
for human consumption) become infected after ingesting
infected materials.
3. Oocysts develop into tachyzoites shortly after ingestion.
4. Tachyzoites spread throughout the body and form tissues
in neural and muscle tissue.
5. Cats become infected after consuming intermediate hosts
containing tissue cysts.
6a. Humans can become infected by:


Ingesting undercooked meat containing tissue cysts
Ingesting food or water contaminated with at feces or other
feces-contaminated materials (eg, soil) or contact with a pet cat's
litter.
7. Rarely, human infection results from blood transfusion or
organ transplantation.
8. Rarely, transplacental transmission from mother to fetus
occurs.
9. In the human host, parasites form tissue cysts, most
commonly in skeletal muscle, myocardium, the brain, and the
eyes; these cysts may remain throughout the life of the host
and can reactive if the host becomes immuno-compromised.
o Cyst-like accumulations of merozoites called bradyzoites in
zoitocyst (cyst) are located in brain tissue.
Not transmitted from
human to human.
Exception: mother to
fetus.
A. Food Borne
Transmission:
The tissue form of the
parasite (microscopic
cyst made up of
bradyzoites) can be
transmitted to humans
via undercooked meat.

PATHOGENESIS
*Acute infection: causes painful
swollen lymph glands in the
cervical, supraclavicular, and
iguinal areas. In heavy acute
infections the organism can be
found free in the blood and
peritoneal exudate.
Symptoms - flu-like
*Subacute: cause extensive lesions
in the lungs, liver, heart, brain, and
eyes.
*Chronic infection: occurs when
the host's immune system decreases
the formation of tachyzoites.
Symptoms - blindness, blind spots,
paralysis and myocarditis
*opportunistic infection in AIDS
patients.
People become infected by:
•Eating undercooked, contaminated meat (especially pork,
lamb, and venison).
•Accidental ingestion of undercooked, contaminated meat
after handling it and not washing hands thoroughly
(Toxoplasma cannot be absorbed through intact skin).
•Eating food that was contaminated by knives, utensils,
cutting boards, or other foods that had contact with raw,
contaminated meat.
B. Animal-to-human (zoonotic) transmission:

Cats play an important role in the spread of
toxoplasmosis. They become infected by eating
infected rodents, birds, or other small animals.

The parasite is then passed in the cat's feces in a
microscopic oocyst.

Kittens and cats can shed millions of oocysts in
their feces for as long as 3 weeks after infection.

Mature cats are less likely to shed Toxoplasma if
they have been previously infected. A Toxoplasmainfected cat that is shedding the parasite in its
feces contaminates the litter box. If the cat is
allowed outside, it can contaminate the soil or
water in the environment as well.
People can be infected by:
 Accidental ingestion of oocysts
after cleaning a cat's litter box
when the cat has shed
Toxoplasma in its feces.



Accidental ingestion of oocysts
after touching or ingesting
anything that has come into
contact with a cat's feces that
contain Toxoplasma.
Accidental ingestion of oocysts in
contaminated soil (e.g., not
washing hands after gardening or
eating unwashed fruits or
vegetables from a garden).
Drinking water contaminated
with the Toxoplasma parasite .
(CDC Photo)
C. Mother-to-child (congenital) transmission
 A woman who is newly infected with Toxoplasma during
pregnancy can pass it to her unborn child via congenital
infection. The woman may not have symptoms, but there
can be severe consequences for the unborn child, such as
diseases of the nervous system and eyes.

Generally if a woman has been infected before becoming
pregnant, the unborn child will be protected because the
mother has developed immunity. If a woman is pregnant
and becomes newly infected with Toxoplasma during or
just before pregnancy, she can pass the infection to her
unborn baby. The damage to the unborn child is often
more severe the earlier the transmission occurs.
Potential results can be:





a miscarriage
a stillborn child
a child born with signs of toxoplasmosis (e.g.,
abnormal enlargement ( hydrocephalus) or smallness
of the head).
Infants infected before birth often show no symptoms
at birth but develop them later in life with potential
vision loss, mental disability, and seizures.
In the human host, the parasites form tissue cysts,
most commonly in skeletal muscle, myocardium,
brain, and eyes; these cysts may remain throughout
the life of the host.
Rare instances of transmission:
 Organ transplant recipients can become infected by receiving
an organ from a Toxoplasma-positive donor. Rarely, people
can also become infected by receiving infected blood via
transfusion.
 Laboratory workers who handle infected blood can also
acquire infection through accidental inoculation.
Symptoms:
 Few people show symptoms due to the immune system keeping
the parasite from causing illness.


"flu-like" symptoms that last for several weeks and then go
away. Immunocompetent individuals may present with fever,
lymphadenopathy, muscle aches, and headache. Congenitally
infected children may suffer impaired vision and mental
retardation. Immunosuppressed patients may have central
nervous system disease (encephalitis).
The parasite remains in the body in an inactive state. It can
become reactivated if the person becomes
immunosuppressed.
DIAGNOSIS
Serologic testing (A test that measures
immunoglobulin G (IgG) is used to determine if a
person has been infected).
 Direct observation of the parasite in stained
tissue sections, cerebrospinal fluid (CSF), or
other biopsy material. These techniques are
used less frequently because of the difficulty of
obtaining these specimens.
 Polymerase chain reaction (PCR) also is useful to
identify T. gondii DNA in CSF, amniotic fluid,
infant peripheral blood, and urine to definitively
establish the diagnosis.
 ELISA

DIAGNOSIS
Diagnosis of acute Toxoplasma infection can be
established by :
• Culture of T. gondii from blood or body fluids.
• Identification of tachyzoites in sections or
preparations of tissues and body fluids.
• Identification of cysts in the placenta or tissues of a
fetus or newborn
• Characteristic lymph node histologic features.
PREVENTION AND CONTROL
Cook food to safe temperatures (66 ° C). A food
thermometer should be used to measure the internal
temperature of cooked meat. Do not sample meat
until it is cooked.
 Freeze meat for several days at sub-zero (0° F)
temperatures before cooking to greatly reduce chance
of infection.
 Peel or wash fruits and vegetables thoroughly before
eating.
 Wash cutting boards, dishes, counters, utensils, and
hands with hot soapy water after contact with raw
meat, poultry, seafood, or unwashed fruits or
vegetables.
 Wash your hands.


If you are pregnant or immunocompromised:
 Avoid changing cat litter if possible or wear
disposable gloves and wash hands with soap
and warm water afterwards.
 Keep cats indoors.
 Do not adopt or handle stray cats, especially
kittens. Do not get a new cat while you are
pregnant.
TREATMENT
Pyrimethamine (Daraprim)
Side effects: bone marrow suppression and liver
toxicity, folic acid antagonist.
 Sulfadiazine: used if unborn child is infected.
 Spiramycin: used to treat pregnant women.
Reduces risk to child. Still experimental in the
U.S.

Interesting facts about toxoplasmosis:
1. Infections in rats and mice can lead to them losing their
fear of cats and indeed being drawn to cats.
2. Infected male humans have a six fold increased risk of a
traffic accident due in part to slower reaction times.
3. Prevalence is affected by climate and climate change may
affect its overall prevalence.
5. Countries where raw meat is more commonly consumed
have higher rates of the infection, unsurprisingly.
6. Epidemiological studies link infectious agents of
Toxoplasma gondii to schizophrenia.