Toxoplasma gondii (T. gondii) is a common intestinal parasite transmitted by cats and is responsible for toxoplasmosis, a disease that felines contract by consuming infected raw meat or through the fecal-oral route. Humans can also become infected with this pathogen by ingesting raw or undercooked parasitized meats, or vegetables contaminated with cat feces. People cannot spread toxoplasmosis, but a pregnant woman can transmit it to her fetus, so specific precautions must be taken during pregnancy to avoid it.
However, a new study has now revealed that T. gondii also poses an increased risk in older adults, as it can contribute to muscle loss, fatigue and other signs of frailty in older adults. The research has been conducted by an international group of scientists including the University of Colorado Boulder, the University of Maryland School of Medicine and the University of A Coruña, and has been published in the Journal of Gerontology: Medical Sciences.
“We often think of T. gondii infection as relatively asymptomatic, but this study highlights that for some people it can have important future health consequences,” said Christopher Lowry, professor in the Department of Integrative Physiology at CU Boulder and co-author of this study, which is the latest to explore the impact of this tiny single-celled organism on human health.
“This article provides, for the first time, evidence of the existence of a link between frailty in older adults and the intensity of the response to T. gondii infection”
As researchers have explained, in some countries more than 65% of adults have been infected by this microorganism and, once infected, people can harbor the parasite for life without knowing it. To carry out this study, they analyzed the blood of 601 Spanish and Portuguese individuals over 65 years of age, and also evaluated measures of a common geriatric syndrome known as ‘frailty’ and includes unexplained weight loss, fatigue, decreased cognitive acuity and other signs indicating deterioration in health.
67% of the participants were “seropositive” and showed blood markers of a latent infection. The researchers did not see an association between any T. gondii infection and frailty, but they did find that, among those infected, those with higher “serointensity,” or a higher concentration of antibodies against the parasite, were significantly more likely to be frail.
Higher serointensity could reflect more virulent or widespread infection, multiple infections, or recent reactivation of a latent infection, the authors explained. “This article is important because it provides, for the first time, evidence of the existence of a link between frailty in older adults and the intensity of the response to T. gondii infection,” highlighted Blanca Laffon, professor of psychobiology at the Interdisciplinary Center of Chemistry and Biology of the University of A Coruña and co-author of the work.
How cats transmit the ‘T. gondii’
Domestic and wild felines are considered to be definitive hosts of T. gondii, while birds and rodents are secondary hosts, so when cats eat these infected animals, the parasite settles and multiplies in their intestines, releasing eggs to through their feces. Therefore, if people are exposed to such feces when, for example, they clean the litter boxes of their domestic cats, they can contract the infection.
Most people never know they have been infected, and only about 10% experience flu-like symptoms for a few days. However, T. gondii typically remains dormant for decades, enveloped in cysts in the tissue. muscular and cerebral (specifically in the amygdala, an area of the brain that is involved in the processing of emotions).
Interestingly, it has been proven that T. gondii can alter the behavior of its host and that, for example, infected rodents tend to lose their fear of felines, which makes it easier for cats to catch and devour them and favors the proliferation of the parasite. . Infected chimpanzees have also been shown to be attracted to the smell of the urine of their feline predator, the leopard.
Infected people also have a greater tendency to engage in risky behavior, and research shows that they tend to be more impulsive and entrepreneurial and more likely to be involved in a traffic accident. They also have higher rates of schizophrenia, and certain mood disorders and cognitive problems, and are more likely to attempt suicide, research by Lowry and Dr. Teodor Postolache, a professor in the Department of Psychiatry at the School of Medicine, shows. from the University of Maryland and lead author of the new study.
Fragility by ‘T. gondii’ associated with a lowering of defenses
The authors have cautioned that their findings do not prove that exposure to T. gondii causes frailty, but rather identifies a relationship that should be further studied, since they discovered that frail people with high seropositivity to T. gondii also had higher levels of certain inflammatory markers, suggesting that infection with the parasite could enhance the inflammation that occurs with aging.
Because T. gondii remains dormant in the body and tends to hide in muscle tissue, Postolache suspects that it could also play a role in accelerating sarcopenia, or age-related muscle atrophy. Additionally, certain medications or diseases that compromise the immune system, such as HIV or cancer, can help a latent infection escape immune suppression and reactivate, causing adverse effects. Even in people with a healthy immune system, Lowry notes, immune function can decline with age, potentially allowing latent T. gondii to reactivate.
The researchers hope their study will inform new research into the relationship between T. gondii and frailty and help develop new strategies to prevent the parasite from causing damage. For now, they encourage the population, and especially pregnant women, the elderly and immunocompromised people, to take measures to prevent infection.
