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984 Toxoplasmosis/Neosporosis

Toxoplasmosis/Neosporosis Client Education
Sheet
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the agent has not been associated with disease
BASIC INFORMATION
neonatal kittens) is characterized by uveitis,
in people. • Clinical infection in cats (as opposed to
Definition chorioretinitis, dyspnea, abdominal disten-
Infections with Toxoplasma gondii or Neospora GEOGRAPHY AND SEASONALITY sion, icterus, fever, stiff gait, hyperesthesia,
caninum, which are obligate intracellular coc- • Worldwide; nonseasonal and neurologic deficits (spinal cord or brain).
cidian parasites that infect mammals, including • Approximately 30% of cats and 15% of dogs • Young dogs (≤1 year old) have generalized
humans in the United States have antibodies against infections resulting in fever, icterus, dyspnea,
T. gondii. and tonsillitis.
Epidemiology • There is a higher prevalence of antibodies • Older dogs more commonly have neuro-
SPECIES, AGE, SEX against N. caninum among rural or farm muscular signs, including muscle atrophy,
Felids are definitive and intermediate hosts for dogs than urban dogs. stiffness, abnormal gait, and multifocal
T. gondii. Clinical Presentation neurologic deficits involving the spinal cord
• All mammals, including dogs, serve as or brain (seizures, ataxia, lower motor neuron
intermediate hosts. DISEASE FORMS/SUBTYPES [LMN] signs, cranial nerve deficits).
• Clinical disease can be severe in transpla- • Subclinical infection is most common result • Arrhythmias or, rarely, heart failure may be
centally or lactationally infected kittens. of infection with T. gondii and N. caninum. present in some older dogs.
• Cats of any age can be affected. • Clinical findings of canine toxoplasmosis Neosporosis:
Dogs are intermediate and definitive hosts for and neosporosis are similar. • Puppies are more severely affected and show
N. caninum. ascending rigid paralysis, with hindlimbs
• N. caninum infections are known to occur in HISTORY, CHIEF COMPLAINT worse than forelimbs.
dogs, cattle, sheep, goats, horses, and deer. Toxoplasmosis: ○ Muscle atrophy and stiffness, muscle
• Puppies are more severely affected, but dogs • Approximately 10% of cats have small contractures leading to arthrogryposis
of any age can be infected. bowel diarrhea for several days after the and hyperesthesia. Cervical weakness,
• Most canine infections are subclinical. first exposure to T. gondii. dysphagia, and variable CNS signs may
• N. caninum antibodies have been detected in • If appropriate immune responses occur, most also be seen.
cats and people, but neither species is known cats and dogs do not develop noticeable • Older dogs may have LMN flaccid paralysis
to develop clinical neosporosis, and exposed clinical signs of T. gondii or N. caninum or show multifocal CNS signs (cranial nerve
cats do not shed N. caninum oocysts. infections. deficits, seizures, blindness).
• Transplacental infection with T. gondii can • Systemic signs include fever, dyspnea, cough,
GENETICS, BREED PREDISPOSITION lead to abortion or stillbirth in dogs or cats. skin lesions, vomiting, icterus, cardiac arrhyth-
It is unclear whether any dog or cat breeds • Kittens infected by the transplacental or mias, megaesophagus, and regurgitation.
are more susceptible to clinical illness from N. lactational routes but survive present as
caninum or T. gondii, and so these agents should fading kittens with nonspecific findings Etiology and Pathophysiology
be on the differential list for all appropriate such as anorexia, lethargy, respiratory distress, • T. gondii exists in three infectious stages:
clinical problems. ocular, and central nervous system (CNS) sporozoites, tachyzoites, and bradyzoites.
signs. ○ Sporozoites occur in oocysts, which are
RISK FACTORS • Dogs and cats with T. gondii infections in excreted in feces, whereas tachyzoites infect
• Ingestion of tissue cysts in prey species is the the postpartum period commonly present all cells with formation of bradyzoites in
greatest risk factor for feline toxoplasmosis. with nonspecific findings of lethargy and tissue cysts as immune responses develop.
• Ingestion of bovine placental tissues or anorexia and occasionally fever. • Transmission can occur through ingestion
sporulated oocysts in canine feces is the • Older dogs and cats with T. gondii infections of infected tissues or ingestion of oocysts in
greatest risk factor for canine neosporosis. can present with anorexia, vomiting, diarrhea, contaminated food or water; transmission can
• Concurrent immunosuppression (from weight loss, lethargy, dyspnea, ocular signs, also occur transplacentally or lactationally
glucocorticoids or antineoplastic drugs) or lameness, possible muscle pain, and signs of (proved only for T. gondii in kittens, not
concomitant illnesses, such as ehrlichiosis, CNS dysfunction (ataxia, paresis, seizures, puppies).
canine distemper, feline leukemia virus cranial nerve deficits). • The enteroepithelial life cycle (and fecal shed-
(FeLV), feline immunodeficiency virus Neosporosis: ding) occurs in cats only after ingestion of
(FIV), feline infectious peritonitis (FIP), • In young dogs (<6 months), particularly intermediate hosts infected with tissue cysts
or Mycoplasma haemofelis infection, may those with transplacental infections, acute or ingestion of sporulated oocysts. Infec-
potentiate clinical illness. However, both ascending paralysis is typical. Dysphagia, tion ultimately results in oocyst formation,
parasites can be primary pathogens. incontinence, and muscle atrophy are also with millions passed into the environment.
seen. Sporulation occurs in 1-3 days, and then
CONTAGION AND ZOONOSIS • Older dogs may present with dermatitis, the oocysts are infectious.
T. gondii is zoonotic: respiratory signs (cough, dyspnea), • The extraintestinal life cycle occurs in all
• Many people are infected by ingesting gastrointestinal (GI) signs, or neurologic hosts, including cats:
sporulated oocysts that contaminate the signs (lameness, seizures). ○ After ingestion of oocysts or tissue cysts,
environment or by ingesting undercooked the organism invades the small intestine
meat. PHYSICAL EXAM FINDINGS and spreads to many extraintestinal tissues
• A healthy cat positive for T. gondii–specific Toxoplasmosis: through blood and lymph, where it causes
antibodies is of little risk to its owner because • Most infections with T. gondii result in no focal necrosis. The CNS, muscles, liver,
it is unlikely to shed oocysts again if exposed. physical exam abnormalities. lungs, and eyes are commonly affected.
N. caninum antibodies have been detected in • Prenatally infected kittens: hepatomegaly, ○ The organism localizes in tissues as cysts,
people, suggesting zoonotic transmission, but ascites, dyspnea, and fever resulting in chronic infection. The cysts

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