Toxoplasmosis is a zoonotic disease caused by a parasite that reaches humans through different animals. Let’s look at the nature of this infection.
- We recommend you read: “Trichomoniasis: causes, symptoms and treatment”
Toxoplasmosis: a silent pathology
There are parasites whose main objective in their life cycle is to infect humans. On the other hand, others end up in it accidentally by contact with contaminated material. This is the case ofToxoplasma gondii, an intracellular protozoan parasite, specialized in infecting various felines.
Knowing the pathogen
Understanding the biology of the pathogenic microorganism is essential to addressing the disease. Therefore, we see it necessary to count some of the most striking general characteristics ofToxoplasma gondii.
This parasite is a very successful protozoan, because unlike many other microorganisms, it is considered generalist in that it iscapable of infecting all homeothermic (warm-blooded) animals. It has three vital forms:
- Oocyst: form of resistance in the environment, about 10 micrometers in diameter.
- Tachyzoito: motor phase of the parasite. It has a semilunar shape of about 5 to 8 micrometers in length.
- Bradyzoite: contained in intratissue cysts. They are a form of resistance inside the body of the host.
All three forms are infective in nature causing toxoplasmosis, and will be found in the host’s body in one phase or another depending on the specific moment of the parasite’s biological cycle.
A complex life cycle
Although it may seem that we are immersing ourselves in a biology lesson, nothing could be further from the truth. Any epidemiologist agrees that knowing the parasite’s life cycle is one of the first prevention barriers to circumventing infection. Here’s a cursory presentation:
- The definitive host is the cat, and therefore, the eggs or oocysts are dispersed through the environment through their feces.
- These oocysts require a sporulation period of one to five days in between. From here, they become infective.
- These forms of resistance are ingested by small rodent mammals or birds, intermediate hosts.
- In them, the parasite takes the form of tachyzoite and then bradyzoite, invading the tissues of the animal in the form of cysts.
- Cats become infected again by consuming these hosts through predation.
This would close the cycle normally. As we can see, the human being does not play any essential role in it, thereforewe are an accidental host. Upon contact with infected animal tissue or cat fecal samples, theToxoplasma gondiiparasite invades the body, generating bradyzoites that can remain for a lifetime. Thus begins the clinical picture of toxoplasmosis.
What transmission routes does it follow?
Knowing how the parasite is transmitted is, without a doubt, the first step to combat it. There are three possible paths.
1. Digestive tract
It is the most common method of infection. Humans can contract the disease by eating raw orsemi-raw meat contaminated with cysts, or by handling food in environments with traces of feces from infected cats.
Various sources have cited that in regions such as South America the main source of infection is water (even treated with chlorine), as oocysts can remain dormant in it.
2. Transplacental route
It occursin one-third of infected pregnant women. Tachyzoites, in the mobile phase circulating in the bloodstream, can reach the placenta and infect the fetus. This can lead to many episodes of miscarriages. In 90% of cases, pregnant women are unaware of their pathology, since the signs and symptoms of acute infection are so insignificant that they do not provoke medical visits.
Therefore, serological screening tests in pregnant women in some areas are mandatory. The transplacental transmission route results in congenital toxoplasmosis, which can be addressed if diagnosed early.
3. Parenteral route
Cases have been reported in which contaminated blood transfusion samples have come to infect the recipient. Even so, it is insisted that this route of transmission isvery rare and of low relevance compared to the previous ones.
Causes
The numbers that toxoplasmosis gives us are, to say the least, dizzying. The prevalence of this disease is 30% globally. However, exposure to the parasite varies in humans from 0 to 100%, depending on the geographic area. We do not have to go to low-income countries to contrast these data, sincein the United States it is estimated that 23% of the population is infected. Other countries such as Brazil are worse off, with an estimated prevalence ranging between 50 and 75%.
However, not all the news is bad, as this trend seems to have diminished in many countries in Europe and the United States. This is probably due to increasingly sophisticated sanitation practices and increased food control.
Symptoms
Toxoplasmosis can be an asymptomatic or serious pathology, depending on the state of the immune system of the sufferer. In non-immunocompromised people, if symptoms occur, they may include:
- Fever.
- Myalgia, muscle pain.
- Inflammation of the lymph nodes.
- Generalized abdominal pain.
- Itchy throat.
A different case is that of people with a variable degree of immunosuppression, for example, because of associated pathologies such as HIV. In these cases, toxoplasmosis can be complicated, leading to leukemias and connective tissue diseases.
A special case is that of this disease in its congenital form, which in newborns or fetuses can cause various symptoms, such as:
- Intrauterine death of the fetus.
- Permanent neurological damage.
- Hydrocephalus, excessive accumulation of cerebrospinal fluid in the skull.
- Retinocorditis, a type of ocular toxoplasmosis that occurs with eye pain, photophobia and inflammation among other symptoms.
Treatment
As we have already mentioned, most cases do not require specific treatment, because the host does not even realize that it carries the parasite. In more obvious clinical manifestations, drugssuch as pyrimethamine or sulfadiazine, both antiprotozoal drugs, may be prescribed.
In the case of congenital toxoplasmosis, ocular, or in people with compromised immune systems, treatment may vary, considering medication for the rest of the patient’s life. We must be aware that, due to its dynamic nature, completely eliminating the parasite from the body is a complicated task.
Conclusions
Toxoplasma gondiiis a pathogen that has a much higher prevalence than we might initially think. Due to its silent nature that usually occurs asymptomatically, it is common foran infected person to never know that he has contracted it.
Therefore, it is essential to perform serological tests on pregnant women in countries where the prevalence of toxoplasmosis is high, because as we have seen, the severity of the pathology increases considerably if it occurs in fetuses. It is also necessaryto refine general sanitation measures in affected populations, as oocysts of this parasite can survive in water or in contaminated terrestrial environments (including food surfaces).
When talking about pathologies generated by protozoan parasites (not viruses or bacteria) the general considerations to take into account to prevent them are usually the same. Protozoa are too large to be transmitted through the air as is the case with other pathogens. Therefore, the best prevention is to control what we touch and the sanitation measures to use before putting something in our mouths.
References
- CDC – Toxoplasmosis. (n.d.). CDC. Retrieved July 9, 2020, fromhttps://www.cdc.gov/parasites/toxoplasmosis/index.html
- Martín-Hernández, I., & García-Izquierdo, S. M. (2003). Toxoplasmosis in man. Biochemistry, 28(3), 19-27.
- Global Water Pathogen project – Toxoplasma gondii. (n.d.). Waterpathogens.org. Retrieved July 9, 2020,http://www.waterpathogens.org/node/158
- Reis Amendoeira, M. R. (2001). Diagnosis of congenital toxoplasmosis. Revista Cubana de Investigaciones Biomedicas, 20(2), 118-121.
- Dodds, E. M. (2003). Ocular toxoplasmosis. Archivos de la Sociedad Española de Oftalmología, 78(10), 531-541.
To the classic question “what do you do?” I always answer “basically I am a psychologist”. In fact, my academic training has revolved around the psychology of development, education and community, a field of study influenced my volunteer activities, as well as my first work experiences in personal services.
