Description

Toxoplasmosis is a zoonotic disease (a disease that can be transmitted

from animals to humans) that is caused by a protozoan parasite

(a microscopic, one-celled organism). Toxoplasmosis can

infect many different organs and cause serious signs of illness.

Toxoplasmosis may also infect an animal without causing obvious

clinical signs.

Cause

Toxoplasmosis is caused by Toxoplasma gondii , which infects

almost all species of warm-blooded animals. Cats are the only animals

that can excrete oocysts (infectious forms) in their feces. The

most common mode of transmission is eating raw or undercooked

meat that contains tissue cysts or oocysts. Transmission across the

placenta or through the mother’s milk is also possible.

When cats ingest tissue cysts, parasites are released and multiply

in their gastrointestinal tract. Oocysts are shed in the cat’s

feces for 1-3 weeks after its first exposure to the parasite. The

oocysts become infective after 24 or more hours outside the cat’s

body. Any animal may then become infected by eating them.

The parasites multiply within intestinal cells and can spread

throughout the body. Parasites may enter any tissue and cause illness.

In addition, cysts may form in muscles. Cysts may remain

dormant for the life of the animal, or they may become activated

and cause illness at a later time.

Cats that are shedding oocysts in feces usually appear healthy.

Cats with other forms of the parasite in their tissues may become ill.

Clinical Signs

Clinical signs may develop more often in animals that are young,

are immune suppressed, or have another infection. Signs are quite

variable, depending on the organ or tissues involved. Weakness,

incoordination, and other neurologic problems may be noted.

Respiratory signs may occur, such as difficulty breathing, increased

respiratory rate, and coughing. Inflammation of one or both eyes

(uveitis) is a common manifestation in cats. If the liver and

pancreas are affected, signs may include fever, decreased

appetite, vomiting, weight loss, and jaundice (yellow color to the

skin and gums). Multiple signs may be seen if the whole body

is affected.

Diagnostic Tests

Diagnosis of clinical toxoplasmosis can be made based on a combination

of several laboratory tests:

• Blood and urine tests are often needed to determine how the

body is affected by the infection.

• Tests for antibodies to toxoplasmosis can be performed on

serum (from blood), cerebrospinal fluid (from a spinal tap), or

aqueous humor (fluid from the eye).

• X-rays of the chest and abdomen and an abdominal ultrasound

may be recommended.

• Microscopic examinations of tissue samples or of cells from

cerebrospinal fluid and the respiratory tract may be helpful in

identifying the organism.

• Cats that are ill do not shed oocysts in their feces, because their

illness is a result of parasites in other tissues, not in the intestinal

tract.

• Other tests may be needed to rule out diseases that cause similar

clinical signs.

TREATMENT AND FOLLOW-UP

Treatment Options

Drugs usually suppress multiplication of T. gondii organisms but

do not clear all of the organisms from the body. Clindamycin (an

antibiotic) is often the drug of choice. Additional supportive care

in the hospital may be needed, depending on the severity of the

clinical signs.

Follow-up Care

Nervous system and ocular signs are often slow to respond. Vision

is often diminished or lost if uveitis is severe. Transmission of

T. gondii can be reduced by limiting exposure to oocysts and tissue

cysts. Feed cats only fully cooked commercial foods. Keep cats

inside to prevent hunting.

Public Health Information

Toxoplasmosis is usually transmitted to humans by ingestion of

undercooked meats or, less commonly, food or water contaminated

with oocysts. The disease is rarely transmitted by direct contact

with cats. People can be exposed by contact with sporulated

(infective) oocysts from litter boxes, gardens, or sandboxes.

To prevent exposure to people, practice good hygiene in food

preparation and cook meats thoroughly. Litter boxes should be

cleaned and treated with boiling water daily, so that oocysts do not

have time to sporulate. Pregnant women and immune-suppressed

people are the most susceptible to toxoplasmosis, so they should

wear gloves and possibly a mask when changing litter boxes, or the

task should be performed by someone else in the household.

Prognosis

Prognosis for animals with widespread systemic disease is guarded

(uncertain). Prognosis may only be determined in some cats by

their response to initial treatment.