Page 1549 - Small Animal Internal Medicine, 6th Edition

CHAPTER 98 Polysystemic Protozoal Infections 1521

clindamycin alone (75 mg/puppy at 9 weeks of age PO q12h
[dose doubled at 13 weeks] for 6 months) lessened clinical
VetBooks.ir signs of disease but did not eliminate the infection (Dubey
et al., 2007b). Four of six dogs with cerebellar disease associ-
ated with N. caninum infection treated with different com-
binations of clindamycin, trimethoprim, sulfadiazine, and
pyrimethamine had a positive response (Garosi et al., 2010).
Ponazuril is a cidal drug and may prove to be effective for the
treatment of neosporosis at 20 mg/kg, PO, daily (Silva et al.,
2016). Treatment of clinically affected dogs should be initi-
ated before the development of extensor rigidity, if possible.
The prognosis for dogs presented with severe neurologic
involvement is grave.

Zoonotic Aspects and Prevention
Neospora caninum antibodies have been detected in people,
but in one study no link was found to repeated abortion
FIG 98.4 (Petersen et al., 1999). In addition, the organism has not
Neospora caninum cyst filled with bradyzoites in canine
central nervous system tissue. been isolated from human tissues, so the zoonotic potential
is still unproven. An epidemiologic link has been shown
between dogs and cattle; efforts should be made to lessen dog
in feces by microscopic examination after flotation or by fecal contamination of livestock feed, and dogs should not be
PCR. The organism can be differentiated from T. gondii by allowed to ingest bovine placentas. Consuming raw meat is
electron microscopy, immunohistochemistry, and PCR. A a risk factor for dogs and should be avoided (Reichel et al.,
multiplex PCR assay that detects both T. gondii and N. 2007). Hunting behavior of dogs should be restricted if pos-
caninum for use with tissues or CSF has been reported sible. Bitches that whelp clinically affected puppies should
(Schatzerg et al., 2003). In a group of dogs with cerebellar not be bred. Glucocorticoids should not be administered to
disease related to N. caninum infection, four of five dogs seropositive animals, if possible, because a potential exists
tested were positive for DNA of the organism by PCR assay for activation of infection.
performed on CSF.
A presumptive diagnosis of neosporosis can be made by
combining appropriate clinical signs of disease and positive FELINE TOXOPLASMOSIS
serology or presence of antibodies in CSF with the exclusion
of other etiologies inducing similar clinical syndromes, par- Etiology and Epidemiology
ticularly T. gondii. Serologic cross-reactivity between T. Toxoplasma gondii is one of the most prevalent parasites
gondii and N. caninum exist in some assays. IgG antibody infecting warm-blooded vertebrates. Only cats complete
titers of at least 1 : 200 have been detected in most dogs with the coccidian life cycle and pass environmentally resistant
clinical neosporosis; minimal serologic cross-reactivity oocysts in feces. Sporozoites develop in oocysts after 1 to 5
occurs with T. gondii at titers of 1 : 50 or higher when using days of exposure to oxygen and appropriate environmental
the immunofluorescent assay test. temperature and humidity. Tachyzoites disseminate in blood
or lymph during active infection and replicate rapidly intra-
Treatment cellularly until the cell is destroyed. Bradyzoites are slowly
Although many dogs with neosporosis die, some have dividing, persistent tissue stages that form in the extrain-
survived after treatment with trimethoprim-sulfadiazine testinal tissues of infected hosts as immune responses attenu-
combined with pyrimethamine; sequential treatment with ate tachyzoite replication. Tissue cysts form readily in the
clindamycin hydrochloride, trimethoprim-sulfadiazine, CNS, muscles, and visceral organs. Bradyzoites may persist
and pyrimethamine; or clindamycin alone. While different in tissues for the life of the host. There are different geno-
doses of have recommended by different authors, adminis- types of T. gondii, which may vary in pathogenic potential,
tration of trimethoprim-sulfadiazine (15 mg/kg PO q12h) partially explaining why even some immunocompetent cats
with pyrimethamine (1 mg/kg PO q24h) for 4 weeks or can become ill.
clindamycin (10 mg/kg PO q8h) for 4 weeks has been used Infection of warm-blooded vertebrates occurs after inges-
frequently treatment of canine neosporosis. If improvement tion of any of the three life stages of the organism or trans-
is noted, treatment should be continued. A 7-week-old Irish placentally. Most cats are not coprophagic and so are infected
Wolfhound with N. caninum–associated myositis had sig- most commonly by ingesting T. gondii bradyzoites during
nificant clinical improvement after 18 weeks of treatment carnivorous feeding; oocysts are shed in feces from 3 to 21
with clindamycin (Crookshanks et al., 2007). In one recent days. Sporulated oocysts can survive in the environment for
study of naturally infected Beagle puppies, administration of months to years and are resistant to most disinfectants