Infectious Disease Compendium

Toxoplasma gondii


A parasite, found in almost all animals. Cats are the definitive host.

There are several linegages, Type II is in Europe. In North America there are atypical genotypes that have been "associated with severe ocular and systemic disease and unusual presentations of toxoplasmosis in immunocompetent patients (PubMed)."

Epidemiologic Risks

Under cooked meat, especially pork, lamb, and wild game (PubMed), and soil contaminated with cat poo. Can be on raw fruits and vegetables.

And camel's milk in herders in Butana area.

Eating under cooked food >> cat excrement; cats are an overrated risk. Except, I suppose, eating raw cat.

Occasionally passed on in transplanted organs. There were cases in France linked to imported horse meat; "Wilbur, I am so sorry."

It also occurs in families (PubMed).

"We evaluated 148 case patients with recent T. gondii infection and 413 control patients. In multivariate analysis, an elevated risk of recent T. gondii infection was associated with the following factors: eating raw ground beef; eating rare lamb; eating locally produced cured, dried, or smoked meat; working with meat; drinking unpasteurized goat’s milk (ick); and having 3 or more kittens (owning, not giving birth to). Eating raw oysters, clams, or mussels was significant in a separate model among persons asked this question (PubMed)."


Acute disease: usually asymptomatic, it can febrile, malaise, night sweats, myalgias, sore throat, maculopapular rash, hepatosplenomegaly disease with lots of lymphadenopathy. Sort of mono without the exudative pharyngitis and monospot.

Patients on biologics can get severe disseminated disease with encephalitis (PubMed).

Reactivation Disease: CNS mass lesions in HIV patient with CD4 < 200 and transplant patients. Myocarditis, pneumonia and eye involvement can also occur in these patients as well.

It can reactivate in patients who receive myeloablative conditioning and with high-dose total body irradiation for stem cell transplant (PubMed).

Transplant patients (who benefit from prevention) (PubMed) and as a manifestation of thymoma (PubMed).

Disseminated disease in the immunoincompetent has a bad outcome (PubMed).

Bad Driving: People who are toxoplasma seropositive have more car accidents than those who are not, except for those who have RhD positive blood. Really: I wonder if I can use that to get out of a speeding ticket. Your honor, its not my fault, it’s the toxoplasma.

And seropositives are more aggressive and impulsive, so no wonder they are bad drivers (PubMed) (PubMed).

The higher the IgG levels in latent disease, the more neurocognitive issues in HIV patients (Pubmed).

And perhaps seizures (PubMed).

And truck drivers? Often seropositive (PubMed). Great. Huge trucks driven at excess speeds by seizing aggressive bad drivers.

And seropositive kids may not be as good at math (PubMed) and may have more mental illness (PubMed) including anxiety disorder (PubMed). Parasites in the brain may be a bad thing if they are in a useful place. Good thing we only use 10% of our brain. Not.

Mental illness? Maybe. Association is not not causation, but the associations are curious (PubMed) especially in light of the other associations and neuro-affinity.


In HIV patients who are seropositive for toxoplasma, disease can be prevented with qd, trimethoprim/sulfamethoxazole or macrolides (not EES) or atovaquone.

CNS disease. Pyrimethamine 200-mg loading dose then 50-75 mg qd PLUS either Sulfadiazine 1-1.5 g q6h OR clindamycin 600 mg q6h AND Folinic acid 10 -150;20 mg qd (up to 50 mg qd),

OR trimethoprim/sulfamethoxazole po

OR IV 3-5 mg (trimethoprim component)/kg q6h

OR pyrimethamine AND folinic acid PLUS either clarithromycin po 1 g q12h

OR atovaquone po 750 mg q6h OR azithromycin po 1200-1500 mg qd

OR dapsone po 100 mg qd.

From a systematic review (PubMed):

"One well-designed trial showed that trimethoprim-sulphamethoxazole was more effective than placebo for clinical recovery of toxoplasma lymphadenopathy in immunocompetent hosts. For toxoplasma encephalopathy, efficacy of pyrimethamine+sulphadiazine and trimethoprim+sulphamethoxazole were similar, whereas pyrimethamine+sulphadiazine versus pyrimethamine+clindamycin showed no difference, irrespective of the outcome. Intravitreal clindamycin+dexamethasone and conventional treatment with oral pyrimethamine+sulphadiazine had similar efficacy with regard to all outcome measures in ocular toxoplasmosis, and intravitreal therapy was found to be safe. Adverse effects seemed more common with pyrimethamine+sulphadiazine. Most trials for encephalitis and ocular manifestations had a high risk of bias and were of poor methodological quality. There were no trials evaluating drugs for toxoplasmosis in pregnancy, or for congenital toxoplasmosis. Pyrimethamine+sulphadiazine is an effective therapy for treatment of toxoplasmic encephalitis; trimethoprim+sulphamethoxazole and pyrimethamine+clindamycin are possible alternatives. Treatment with either oral or intravitreal antibiotics seems reasonable for ocular toxoplasmosis. "

Once therapy is complete, secondary prophylaxis should be continued indefinitely (in HIV patients on HAART, if CD4 > 200 and viral load <50 for a year, can stop prophylaxis).

I am not going to give advice for treatment in pregnancy, here is the review (PubMed).


In HIV, CNS mass lesions are usually between toxoplasma and CNS lymphoma, toxoplasma tends to be multiple and seropositive; lymphoma tends to be single and sero negative. If single lesion and seropositive, patients should improve clinically in 10 days or so on therapy, if they do not, or worsen, strongly consider biopsy. There is also an interesting literature showing an association between toxoplasmosis and schizophrenia. Really. Or so the voices tell me.

In mice it makes the animals less fearful and more likely to be et, thus completing the parasites lifecycle.

Curious Cases

Relevant links to my Medscape blog

Don't change the litter box before driving.


A Return to the bad old days

The Attic is Full

Last Update: 12/03/18.