Toxoplasmosis - Symptoms, IgG and Treatment

Toxoplasmosis is a disease caused by the parasite Toxoplasma gondii, present in the whole planet and with a high prevalence in the world population. To get an idea of how common is toxoplasmosis infection, it is estimated that about 1/3 of the world's population has already come into contact with this parasite. And toxoplasmosis is not a disease restricted only to developing countries; about 80% of the population of Paris and 70% of the Americans present positive serology for this protozoan.

Toxoplasma gondii
Toxoplasma gondii

But if toxoplasmosis is such a common disease, why do we hear so little talk about it? In fact, most people's immune system is strong enough to stop Toxoplasma gondii from doing us any harm. This fact explains why a large part of the population has IgG antibodies against toxoplasmosis (I explain what is IgG toxoplasmosis below), without ever suspecting having had contact with the parasite.

The major concern regarding toxoplasmosis is in pregnant women and immunosuppressed patients, ie, with weakened immune systems such as transplanted, HIV positive, patients on chemotherapy or immunosuppressive drug use.

Transmission of toxoplasmosis

The parasite Toxoplasma gondii can infect any warm-blooded animal, including humans, however, it is only in cats that it manages to complete its reproductive cycle. In other words, any mammal or bird can have toxoplasmosis, but the parasite only produces eggs (called oocysts) inside the intestines of cats. Felines are called primary hosts; all other animals are intermediate hosts, since they only have the adult parasite in their organism.

The toxoplasmosis transmission cycle occurs as follows: a cat ingests Toxoplasma gondii; which is lodged in its intestines and begins to reproduce, releasing eggs (oocysts) of toxoplasma through the feces. These eggs stay on the ground until some animal swallows them. In the case of humans, the ingestion of these eggs usually results from contamination of the hands on the soil, followed by contact with the mouth. In fact, all diseases caused by the fecal-oral route, such as, for example, hepatitis A and H.pylori, are usually transmitted by hands inadvertently contaminated with feces.

Eating foods like fruits and vegetables from soil contaminated with cat feces is also a transmission route. Washing the food well before eating it is an effective measure to reduce the transmission of toxoplasmosis.

The toxoplasma gondii parasite also seems to be carried by flies and cockroaches that, when they come in contact with contaminated cat feces, can transport the oocytes over long distances.

An important fact is that the oocyte only becomes infective after 24-48 hours in the soil. Therefore, it is important to clean the litter boxes daily of cats in order to prevent toxoplasma eggs from becoming viable for transmission.

Other animals, although not disseminating toxoplasma eggs through the environment such as cats, may also be the transmission routes of toxoplasmosis. Once the parasite is lodged in the tissues of contaminated animals, we only have to eat meat that has been barely passed from them so that the toxoplasma enters our organism. The main meat with risk of transmission are pork, mutton and deer. It is important to note that the animal does not need to be sick to have toxoplasma in its tissues. As occurs in human nodes, having an intact immune system, toxoplasma is present in animals without causing disease, only asleep in their tissues. If your meat is not well cooked, the parasite survives and contaminates the digestive tract of who is ingesting it.

The simple act of handling raw meat with toxoplasm is enough to contaminate hands and cooking utensils like knives and dishes. A cook who prepares a meat with toxoplasma, if he does not wash his hands, can contaminate himself and other dishes that he prepares.

The third mode of transmission of toxoplasmosis is by blood transfusion or by transplantation of organs from contaminated donors to uncontaminated recipients.

There is still the transmission route during pregnancy, but this will be discussed separately in another text to be published briefly.

Symptoms of toxoplasmosis

Up to 90% of healthy people who become infected with toxoplasma gondii, regardless of the route of transmission, will remain asymptomatic indefinitely. In those few immunocompetent people, that is, with a healthy immune system that develops the disease toxoplasmosis, the clinical picture is usually mild, with symptoms similar to a non-specific influenza picture with fever, muscle pain, tiredness, headache and rash cutaneous. The most characteristic symptom is an enlargement of the lymph nodes (ganglia) of the neck. Up to 30% of symptomatic cases usually have enlarged lymph nodes throughout the body. Some cases also have sore throats, becoming very similar to a mononucleosis.

Unlike common viral pictures, symptomatic toxoplasmosis usually lasts for a few weeks, in some cases up to months.

Rarely toxoplasmosis can cause more serious problems in healthy patients such as lung, heart and eye lesions, called respectively pneumonitis, myocarditis and chorioretinitis.

Regardless of whether symptoms occur or not soon after contamination, the immunocompetent patient who acquires the parasite remains asleep in the tissues of the body, usually muscles and nervous tissues, for the rest of their lives. Toxoplasm remains inactive for years, controlled by the immune system, only waiting for any problem that reduces our natural defenses to re-attack our body.

Symptoms of toxoplasmosis in immunocompromised patients

Immunocompromised patients are those with a weak immune system, as in the following cases:
  • HIV and AIDS
  • Cancer and chemotherapy
  • Transplanted patients
  • Patients on immunosuppressive drugs such as corticosteroids

In this group of patients, toxoplasmosis is a very serious disease, since the immune system is deficient and unable to prevent parasite proliferation.

In immunocompromised patients, toxoplasmosis may be a newly acquired disease, but it is most often a reactivation of a chronic infection that spent years in silence while the immune system was still intact, and now takes advantage of low immunology to attack the body.

Toxoplasma brain injury is the most common in immunocompromised patients. Symptoms of cerebral toxoplasmosis include convulsions, changes in gait, speech, limb movements, and mental state, and can often be confused with a stroke. The patient may also develop dementia and even develop into a coma.

Other common lesions of toxoplasmosis in immunosuppressed patients are chorioretinitis, which causes ocular pain and loss of vision; pneumonitis, with fever, shortness of breath and dry cough; myocarditis, with symptoms of heart failure. If untreated, toxoplasmosis can lead to immunosuppressed deaths.

Serological diagnosis

The diagnosis of toxoplasmosis is usually made by serology, that is, by the dosage of antibodies against toxoplasma gondii.

Here's a quick parenthesis to explain how the serology of toxoplasmosis (and several other infectious diseases) works. The reasoning is this: our body only creates antibodies against a particular germ if we are exposed to it. Therefore, having antibodies against toxoplasmosis means having been contaminated by the parasite.

To summarize an extremely complex process, we can say that our body basically works with two antibodies, called IgM and IgG. As soon as a new germ enters our body, our immune system begins to produce the IgM antibody, which is called the acute phase antibody. Having IgM positive for toxoplasmosis means that the disease has been acquired very recently (IgM comes with only 1 week of contamination). After about 4 weeks, the body replaces the IgM antibody with the IgG antibody, which is stronger and more specific against the disease desired. Therefore, after 4 weeks, the patient ceases to have positive IgM and only has IgG positive for toxoplasmosis. This IgG for toxoplasmosis will be positive for the rest of the life.

In summary, a patient with acute toxoplasmosis has IgM positive, whereas a patient who has the inactive parasite in the body will have positive IgG. Those who have never been exposed to toxoplasma have IgM and IgG negative.

As toxoplasmosis does not cause disease in 90% of people, the only way to know if the patient has ever been exposed to toxoplasm is through the dosage of IgG to toxoplasmosis. To know if the person has had toxoplasmosis, even if asymptomatic, is very important information for pregnant women.

Treatment of toxoplasmosis

Obviously, people with asymptomatic toxoplasmosis do not need any type of treatment. Having inactive toxoplasma in the body does not mean being sick. Treatment is also not indicated for those with mild flu-like symptoms that last for a few weeks.

Treatment is indicated only in symptomatic cases, immunosuppressed patients and pregnant women. The first line regimen is made with Pyrimethamine + Sulfadiazine or Pyrimethamine + Clindamycin for 4 to 6 weeks.

Serious immunosuppressed patients should do prophylaxis to prevent reactivation of toxoplasma. The scheme is the same, only with lower doses.

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