Veterinary Medicine - November 2007 - (Page 720)

A challenging case O P E E R - R E V I E W E D tion of red blood cells and inflammatory cells together with a dilated iris.17 Prevalence of T. gondii infection and clinical signs It is estimated that about 30% of people and cats have been exposed to T. gondii in the United States.9 However, immunocompetent people are generally asymptomatic. Studies have shown no direct correlation between human toxoplasmosis and cat ownership.9 Some studies have shown that as many as 74% of cats with uveitis are seropositive for T. gondii depending on Iridotomy Laser iridotomy was performed in this cat to control the IOP in the right eye. The potential complications associated with iris surgery include hemorrhage, the iridotomy sites resealing, and iris bombé recurrence.10 Gonioscopy was not performed to document that the angles were opened postoperatively; Atropine overuse can decrease tear production and cause glaucoma. however, the IOP in the right eye stabilized and eventually decreased, and the iris bombé resolved after the procedure was performed. Because the right eye was already blind, these results were considered successful. the geographic area. 18 Uveitis may occur in healthy cats recently exposed to T. gondii; it is unknown why some develop ocular pathology while others do not. The severity of disease is thought to be associated with a host’s ability to mount a proper cell-mediated immune response, the severity of the primary infection, and the T. gondii strain.19 Neonatal T. gondii infection can cause transient anterior uveitis and, more commonly, chorioretinitis in kittens; it is unknown what role infection in utero plays in chronic or recurrent uveitis in adult cats.18 Clinical signs of T. gondii infection vary in cats: in one study of 100 cats, 36 had multiorgan involvement, 26 had mostly pulmonary signs, 16 had abdominal involvement, and seven had neurologic signs.20 Route of T. gondii infection In this patient, the T. gondii infection was probably acquired by hunting. Toxoplasma gondii is an intracellular protozoan, and cats are the definitive host. Cats become infected by ingesting cysts from the tissue of intermediate hosts (usually rodents). 2 After ingestion, encysted bradyzoites transform into tachyzoites and undergo the sexual phase of their life cycle in the feline intestine. This phase occurs when oocysts are shed in the feces.14 People may become infected by ingesting or inhaling the oocysts in cat feces or by ingesting undercooked red meat. Most cats become infected through hunting and will shed oocysts after initial infection for less than three weeks.9 Litter boxes should be cleaned out daily as it takes 24 hours for oocysts to sporulate and become infective. By the time a cat shows signs of toxoplasmosis, it is no longer shedding oocysts. examination may show oocysts if the cat is actively shedding. However, serum antibody testing is necessary to confirm the diagnosis. The cat in this case had a high normal globulin concentration and a lymphocytosis, but it was the high IgM concentrations against T. gondii that confirmed the diagnosis. Since IgM is not detectable nine weeks after infection, high IgM concentrations indicate recent infection.4 A positive IgM titer or a fourfold increase in IgG titers verifies recent infection. The cat’s IgG concentrations were indicative of either exposure or infection. IgG antibodies develop about two weeks after infection; they may remain elevated for years even in healthy animals. About 53% of healthy cats have tested positive for IgG antibodies to Toxoplasma species.7 Thus, high IgG titers do not prove recent or active infection. Conversely, studies have shown that a positive IgM titer was present in only 1.2% of healthy cats.21 After exposure in experimentally infected cats, a peak rise in IgG titers was reached in two to three weeks. 9 Ideally, this cat’s IgG titer would have been rechecked two to three weeks later to document a rise in convalescent titers. PCR testing to detect the Toxoplasma species DNA in the aqueous humor may also have confirmed the diagnosis.2 However, the clients declined further testing. Treating toxoplasmosis Azithromycin was chosen in case this cat had bartonellosis or toxoplasmosis. Systemic drugs used to treat toxoplasmosis are protozoal-static and only influence the tachyzoite phase; thus, they will not kill tissue cysts and will not prevent recurrent infection. Clindamycin may also be used to treat T. gondii infection.22 Diagnosing toxoplasmosis If T. gondii infection is present, a complete blood count may reveal nonregenerative anemia and leukocytosis. A serum chemistry profile could reveal hypoalbuminemia, hyperglobulinemia, or elevated alanine transaminase, alkaline phosphatase, aspartate transaminase, or creatine kinase activity.9 A fecal PROGNOSIS The prognosis for toxoplasmosis varies depending on the tissues affected and the age at which the cat is infected. Adults that ingest bradyzoites may develop self-limiting diarrhea or be asymptomatic. However, T. gondii in- 720 November 2007 VETERINARY MEDICINE

Table of Contents Feed for the Digital Edition of Veterinary Medicine - November 2007

Veterinary Medicine - November 2007 Contents Leading Off The Veterinary Medicine Interview: Dr. Lila Miller Clinical Exposures Idea Exchange A Challenging Case: Uveitis and Secondary Glaucoma in a Cat Is it Immune-Mediated Neutropenia? Pimobendan Treatment in Dogs with Congestive Heart Failure CE Form Product Preview Advertiser Index Marketplace/Classifieds Mind Over Miller Special Supplement by Lilly: Flea Bite Facts Q&A

Veterinary Medicine - November 2007

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