The Case of One Street Cat with Toxoplasmosis
By Sarah Levine, VMD

Toxoplasma gondii (T. gondii) is an obligate intracellular coccidian parasite that can infect all warm-blooded animals. T. gondii infection is seen in widespread mammalian and avian species⁽¹⁾. The cat family is the only definitive host and therefore the main reservoir for the disease⁽³⁾. Toxoplasma gondii is one of the most common small animal zoonoses. Thirty to forty percent of adult humans throughout the world are seropositive for T.gondii⁽²⁾. Veterinarians serve as an important source of information regarding the risk for the zoonotic transfer of T. gondii to humans. 

Case Study:
A 1 ½ year old, male, street cat presented to Dr. Hagai Almagor, of Jerusalem, for a second opinion  due to neurologic abnormalities and decreased appetite. A physical exam showed that the cat was  dehydrated and ataxic in both rear legs but reflexes were normal and deep pain was present. The cat  also suffered from head spasms and his pupils were minimally responsive to darkness and light. The cat  was treated previously with steroids, but this therapy did not prove successful.  
 
Dr. Almagor started the cat on fluid therapy with vitamin additives, nutritional support and antibiotics.  He also drew blood for a full blood profile including a toxoplasma titer. CBC results revealed a  regenerative anemia, leukocytosis (neutrophilia) and severe thrombocytopenia. The chemistry was  nonremarkable. The Toxoplasma gondii titer (ImmunoComb^® IgG antibody test kit) was positive with  a result of S4 (the highest score being a S6).   

The cat was then immediately treated with clindamycin.  His appetite improved initially and then waned.  He refused to drink and therefore received fluids subcutaneously. The cat also often made heartbreaking  cries. Despite the care given, the cat’s condition did not improve. He died 1 week after onset of  treatment. It is unclear if all the clinical signs were due entirely to systemic toxoplasmosis and neural  tissue damage or if there was some other disease going on simultaneously.  

Lifecycle:
There are three identified stages: (1) tachyzoites=rapidly multiplying form, (2) bradyzoites=tissue cyst  form, (3) sporozoites= within oocysts. Cats become infected either by ingestion of meat/prey with  bradyzoites (cysts) within muscle tissue, ingestion of oocyst contaminated food or water or in-utero.  Oocysts can be seen in the feces by 3 days post-infection and can be released for up to 20 days.  Oocysts are excreted in the feces in high numbers only during the first week after infection⁽¹⁾. These  oocysts, once exposed to air for greater than 48 hours, become infectious to other animals and can  persist in the environment for as long as 1 year.  

A healthy cat’s immune system is generally able to control the infection. Young or immunocompromised  animals (i.e. cats that are FeLV + and FIV +) are unable to control the spread of disease and often  suffer from generalized toxoplasmosis⁽³⁾. Cats born and raised outdoors usually become infected with  T. gondii shortly after weaning and begin to hunt⁽¹⁾. Domestic cats under 1 year produce the largest  number of T. gondii oocysts.  

Clinical Signs:
Clinical signs depend on the number of tachyzoites, the organs affected, the degree and localization  of tissue damage and the activity of the host’s immune system. In cats, lethargy, anorexia, uveitis and  dyspnea secondary to pneumonia are the most common symptoms. Clinical signs are diverse and are  often due to infection of the pulmonary system, CNS, hepatic, pancreatic, cardiac and ocular tissue⁽⁴⁾.   

Treatment:
Clindamycin hydrochloride is the drug of choice for the treatment of toxoplasmosis in cats and dogs  at the dose of 10-12mg/kg PO for 4 weeks. Administration of clindamycin to an actively shedding cat  can help reduce levels of oocysts released⁽²⁾. Clinical signs in animals with systemic illness usually  resolve within 24-48 hours after the onset of treatment.  

Diagnosis:
Diagnosis is dependent on demonstration of the organisms (histopathology) or indirect serologic  evidence (complement fixation, direct or indirect HA, ELISA, IFA). Routine hematologic, biochemical  and radiographic abnormalities vary depending on which tissue is affected and to what extent.  IgM  appears early but does not persist past 3 months post-infection. IgG appears 4 weeks post-infection  and can remain for years⁽²⁾. Histopathologic changes of affected tissues and identification of tachyzoites  or bradyzoites can confirm diagnosis. CSF and aqueous humor can be used for detection of bradyzoites  and tachyzoites. 

Antemortem diagnosis is based upon a combination of serologic and clinical parameters such as:  recent or active infection as seen by a high IFA IgM titer (>1:256) or IgM ELISA of 1:64 and negative IgG  ELISA or a four-fold rise in IgG titers, positive response to symptomatic therapy, or exclusion of other  causes of clinical signs⁽⁴⁾.  There is no serological assay that accurately predicts when a cat will shed T.gondii oocysts or when they have shed in the past. Most cats that are shedding oocysts are  seronegative⁽²⁾. Most seropositive cats have completed the oocyst-shedding period and are unlikely to  repeat shedding^(2,5).   

Zoonosis:
Humans can become infected with oocysts when they ingest contaminated food or water.  Raw fruits  and vegetables, as well as raw goats milk have been proven sources of infection. Contact with soil (e.g.,  gardening without gloves) that contains oocysts results in an increased risk of infection with T. gondii.  Ingestion of non-fully cooked meat that contains tissue cysts is the most common avenue for human  infection. Pork is the most common meat to contain tissue cysts but poultry, goat and lamb can also be  sources of
infection⁽¹⁾.   Immunosupression may make a host more susceptible to infection because T.gondii is an opportunistic  pathogen⁽⁴⁾. Clinical disease is more severe in immunosuppressed individuals like fetuses, people with  AIDS, or people being treated with immunosuppressive agents for the treatment of cancer⁽²⁾. People with  positive IgG titers to T. gondii are immune to any future infection. Therefore, women should have their  titers checked prior to becoming pregnant.  Although cats are the only definitive hosts for T.gondii, it is highly unlikely that a person will acquire toxoplasmosis from their personal cat⁽²⁾. Cats only shed oocysts once and for only a short fraction of their lifespan⁽²⁾.  Epidemiologic studies have shown that it is unlikely that someone can become infected by petting a cat nor is transmission likely via cat bites and scratches⁽¹⁾. Cat ownership is not associated with an increase in toxoplasma seroconversion, even in HIV-infected patients^(1,5).

Prevention:      
If there is a cat in the household, there are basic precautions that can be taken to insure the safety of the fetus, immunosuppressed individuals or anyone in the family:    
»  All water should be boiled or filtered prior to drinking.   
»  All vegetables and fruits should be thoroughly washed before eating.   
»  Gloves should be worn while working with soil.    
»  Children’s sandboxes should be covered while not in use.   
»  Freezing meat at –12° C for several days will kill most tissue oocysts.    
»  All meat should be fully cooked before eating.   
»  The family cat’s litter box should be cleaned daily; oocysts require at least 48 hours to become infectious.  
»  Immunosuppressed or pregnant cat owners should not clean the litter box.    
»  Household cats should not be fed any raw meat and should be kept indoors to prevent predation and the possibility of infection.   
»  All T. gondii is heat labile (150° F/ 65° C) and can be destroyed with boiling water, 10% ammonia or iodine.

References:
1)  Lindsay, David. (2004). Toxoplasma gondii and feline toxoplasmosis. Proceedings Western Veterinary Conference.
2)  Lappin, Michael. (2001). Enteric Zoonoses. Proceedings Western States American Veterinary  Association.
3)  Aiello, Susan, E. & Mays, Asa (Eds.). (1998). The Merck Veterinary Manual (8th edition). Merck &  CO., INC.: USA.
4)  Jergens, Albert E. (2003). Clinical update on giardiasis, toxoplasmosis, and cryptosporidiosis.  Proceedings Western Veterinary Conference.
5)  Wolf, Alice M.  (2002). Zoonosis or not? What you, employees, and clients need to know.  Proceedings Atlantic Coast Veterinary Conference.       

For any further information please contact us at: info@biogal.co.il  


Technical Tip:  When Performing More than One Test
This tip is geared mainly for our customers, who test more than one sample at a time. Those of you who use a few teeth of the ImmunoComb^® on one occasion rather than one tooth could apply this tip in their work. To avoid confusion when performing the test in such a way, please follow these suggestions:

»       Pay a careful attention to avoid touching the Comb’s teeth with your fingers in any time.
»       Cut off the needed number of the Comb’s teeth (if necessary).
»       Write above each tooth the suitable name/number of your patient(s) using a waterproof pen or a pencil (a ballpoint pen will not work).   

If you have any question, please do not hesitate to contact us at info@biogal.co.il.