Page 1552 - Small Animal Internal Medicine, 6th Edition

1524 PART XIV Infectious Diseases

administration of a drug with anti–T. gondii activity may be BOX 98.1
beneficial.
VetBooks.ir resolve within the first 2 to 3 days of clindamycin or Prevention of Human Toxoplasmosis
Clinical signs not involving the eyes or the CNS usually
Prevention of Oocyst Ingestion
azithromycin administration; ocular and CNS toxoplas-
mosis respond more slowly to therapy. If fever or muscle Avoid feeding undercooked meats to cats.
hyperesthesia does not decrease after 3 days of treatment, Do not allow cats to hunt.
other causes should be considered. Recurrence of clinical Clean the litter box daily, and incinerate or flush the
signs may be more common in cats treated for less than feces.
4 weeks. No evidence suggests that any drug can totally Clean the litter box periodically with scalding water or
use a litter box liner.
clear the body of the organism, so recurrences are common Wear gloves when working with soil.
and infected cats will always be seropositive. The prog- Wash hands thoroughly with soap and hot water after
nosis is poor for cats with hepatic or pulmonary disease gardening.
caused by organism replication, particularly in those that are Wash fresh vegetables well or cook before ingestion.
immunocompromised. Keep children’s sandboxes covered.
Boil water for drinking that has been obtained from the
Zoonotic Aspects and Prevention general environment.
Toxoplasma gondii is a major zoonosis. Primary infection of Control potential transport hosts.
mothers during gestation can lead to clinical toxoplasmo- Treat oocyst shedding cats with anti-Toxoplasma drugs.
sis in the fetus; stillbirth, CNS disease, and ocular disease Prevention of Tissue Cyst Ingestion
are common clinical manifestations. Primary infection in Cook all meat products to 66° C.
immunocompetent individuals results in self-limiting fever, Wear gloves when handling meats.
malaise, and lymphadenopathy. As T-helper cell counts Wash hands thoroughly with soap and hot water after
decline, approximately 10% of people with AIDS develop handling meats.
toxoplasmic encephalitis from activation of bradyzoites in Freeze all meat for a minimum of 3 days before cooking.
tissue cysts.
People most commonly acquire toxoplasmosis transpla-
centally or by ingesting sporulated oocysts or tissue cysts.
Avoiding the ingestion of undercooked meats and carefully • Cats are quite fastidious and usually do not allow feces
washing or cooking produce are two of the most impor- to remain on their skin for periods long enough to lead
tant ways to prevent toxoplasmosis (Box 98.1). In a study of to oocyst sporulation; the organism was not isolated
6282 meat samples from 698 retail meat stores, T. gondii was from the fur of cats shedding millions of oocysts 7 days
not found in any of the beef or chicken samples tested (by previously.
bioassay in cats) and only a small number of pork samples • Increased risk of acquired toxoplasmosis was not associ-
were positive (Dubey et al., 2005). However, the organism ated with cat ownership in people with AIDS or in most
has been detected in tissues from free-ranging chickens that studies of veterinary health care providers.
were likely infected by ingestion of sporulated oocysts (Gon-
çalves et al., 2012). Sporulated oocysts are also infectious, However, in the minority of studies evaluating risk factors,
so ingestion of materials that may be contaminated with old the association between cat contact and toxoplasmosis has
cat feces (e.g., contaminated soil or unwashed vegetables) been made. For example, the risk was associated with owning
should be avoided. There is also an association between three or more kittens in one study (Jones et al., 2009). Thus
toxoplasmosis and ingestion of certain uncooked shellfish hands should always be washed after handling kittens and
that can concentrate the organism from contaminated water cat feces. If a fecal sample from a cat is shown to contain
(Jones et al., 2009). Touching individual cats is probably not oocysts measuring 10 × 12 µm, the organism is assumed
a common way to acquire toxoplasmosis for the following to be T. gondii. The feces should be collected daily until the
reasons: oocyst-shedding period is complete. Historically, adminis-
tration of clindamycin (25-50 mg/kg PO divided q12h) can
• Cats generally only shed oocysts for days to several weeks reduce levels of oocyst shedding. Because human beings are
after primary inoculation. not commonly infected with T. gondii from contact with
• Reactivation of oocyst shedding is rare in cats with chron- individual cats, testing healthy cats for toxoplasmosis is not
ically infected healthy cats, even in cats treated with clini- recommended. Fecal examination is an adequate procedure
cal doses of glucocorticoids or cyclosporine, or in those to determine when cats are actively shedding oocysts but
infected with feline immunodeficiency virus or feline cannot predict when a cat has shed oocysts in the past. No
leukemia virus. serologic assay accurately predicts when a cat shed T. gondii
• Repeat shedding can occur if chronically infected cats are oocysts in the past, and most cats that are shedding oocysts
re-exposed, but generally smaller numbers of oocysts are are seronegative. Most seropositive cats have completed the
shed (Zulpo et al., 2018). oocyst shedding period and are unlikely to repeat shedding;