Toxoplasmosis is a significant public health issue because it can infect both animals and humans. The Toxoplasma organism is carried by domestic cats which then transmit the disease to other warm-blooded animals and humans. Understanding of the Toxoplasma life cycle and transmission can aid in the prevention of disease.
What causes Toxoplasmosis?
Toxoplasmosis is a disease caused by the intracellular coccidian protozoan parasite Toxoplasma gondii. Its definitive host is the domestic cat. Cats usually become infected by ingesting Toxoplasma organisms present in the tissue (meat) of an intermediate host, such as a mouse. The protozoa then rapidly multiply within the cat’s gut. Three to ten days later, the cat begins shedding oocysts (eggs) in its faeces.
Cats that have been exposed to Toxoplasma before will have some immunity and are less likely to shed infected faeces. When intermediate hosts (e.g. rodents, sheep, cattle, pigs, birds, etc.) ingest the oocysts, they become infected. However, Toxoplasma cannot reproduce in intermediate hosts as it does in the cat, so these animals will not produce infected faeces.
What are the signs of Toxoplasma infection?
Animals that harbour a Toxoplasma infection will not always show signs of illness. Despite the prevalence of exposure in the cat population, few cats actually become clinically ill. Cats are more likely than dogs to show signs of the disease, especially younger cats. The most commonly reported signs are:
• Loss of appetite
• Depression or lethargy
• Weight loss
• Ocular (eye) disease
• Respiratory distress
• Neurological signs (difficulty walking and balancing, seizures, tremors, etc.)
• Digestive upsets (vomiting, diarrhoea, abdominal pain)
• Enlarged lymph nodes (“glands”)
• Weak or stillborn kittens (this occurs sometimes when pregnant cats become infected)
How is Toxoplasmosis diagnosed?
Diagnosis of toxoplasmosis is quite difficult. Many of the symptoms seen in toxoplasmosis are common to other diseases as well. Moreover, testing for toxoplasmosis is often problematic.
There are two methods of testing:
1. Faecal Sample: faecal samples are examined for the presence of infective protozoa. This is not a reliable method of diagnoses as many animals will have ceased shedding Toxoplasma organisms in their faeces by the time they show clinical signs.
2. Serology: is the most definitive means of diagnosing toxoplasmosis. Multiple blood samples are taken and tested for signs of an active infection.
Can toxoplasmosis be treated?
The usual treatment for toxoplasmosis is with the antibiotic clindamycin. Antibiotic therapy should continue at least 2 weeks after the clinical signs have resolved. Some animals will experience side effects from the drug such as loss of appetite, vomiting, and diarrhoea.
Other drugs that are occasionally used are sulfadiazine and pyrimethamine. If the disease is promptly and aggressively treated, the animal has a good chance of recovering. Some extremely ill animals (those with severe neurological and muscle damage) may have chronic debility.
How can I prevent my cat from becoming infected with Toxoplasma?
Cats become infected with Toxoplasma by ingesting meat that contains Toxoplasma cysts. Do not feed raw or undercooked meat to your pet. Prevent cats from roaming and hunting prey like birds and mice by keeping them indoors.
How do people become infected with Toxoplasma?
There are a number of ways that people can become infected with Toxoplasma:
1. Eating raw or undercooked meat from an infected animal
2. Eating food or drinking water that has been contaminated with cat faeces
3. Toxoplasma can be transferred across the placenta to the unborn child when a pregnant mother becomes infected with Toxoplasma
Individuals who are particularly at risk are pregnant women and people with compromised immune systems. They should take extra precautions to avoid infection.
How can people avoid becoming infected with Toxoplasma?
As with cats, a large proportion of the human population have been exposed to Toxoplasma at some point in their life, though few people actually become ill. A healthy cat that is positive for Toxoplasma poses little risk for its owner. However, there are a few precautions you can take to minimize the risk of Toxoplasma infection:
1. Never eat raw meat or feed it to your cat
2. Wash hands and any surfaces that have been in contact with raw meat
3. Keep cats out of sandboxes
4. Wear gloves when gardening (to avoid contaminated soil)
5. Empty cat litter boxes daily (oocysts need at least 24 hours to become infective)
6. Pregnant women should avoid contact with cats that are shedding infective oocysts in their faeces, should not empty cat litter boxes (or use gloves), and should stay away from raw meat.