Ep 39 Toxoplasmosis: Calling All Cats

Early detection and prevention of toxoplasmosis during pregnancy could have significantly improved the life of Janet Morell's daughter, Dana. Janet shared her heart-wrenching story before the Illinois State Senate in support of a bill that would require healthcare professionals to provide counseling and testing for toxoplasmosis during pregnancy. Dana was born with severe brain and eye damage due to the disease, and her life has been filled with numerous surgeries, constant care, and challenges. The toll on her body and her family's emotional and financial well-being has been tremendous. This episode of "This Podcast Will Kill You" covers Toxoplasma gondii and the importance of awareness and prevention of this disease during pregnancy. The hosts, Erin Welsh and Erin Ullman Updike, shared their experiences of attending live shows at the University of Florida and the University of Michigan and being a guest on another podcast, "The Road to Now." They also introduced a quarantini recipe for listeners to enjoy.

Toxoplasma gondii is a single-celled parasitic organism that infects up to one third of the world's population. The main hosts of this parasite are cats, which excrete infectious oocysts in their feces. These oocysts can persist in the environment for years and can contaminate food and water, leading to infection in small animals, such as mice and rats. Inside these animals, the parasite transforms into tachyzoites and replicates rapidly, eventually invading muscle and brain tissue. The ideal environment for Toxoplasma gondii is subtropical, and it can survive in various climates. Humans can become infected by consuming undercooked meat or contaminated water or soil. It's important to note that while Toxoplasma gondii is technically an epidemiological topic, its biology is fascinating and complex, making it worth exploring in depth.

The parasite Toxoplasma gondii exhibits an intriguing ability to manipulate the behavior of its intermediate hosts, such as mice and rats, to increase the chances of being consumed by the definitive host, cats. Once inside the muscle or brain tissue of these animals, Toxoplasma gondii transforms into a slow-dividing stage called Bradyzoites, which form cysts. These cysts contain numerous Bradyzoites, which continue to divide, ensuring the parasite's presence in the tissue. The parasite's manipulation of the behavior of intermediate hosts is a strategy for ensuring its transmission to the definitive host, as only in cats can Toxoplasma gondii sexually reproduce and complete its life cycle. Humans, being the intermediate host, can get infected with various stages of the parasite, but since we cannot complete its life cycle, we remain an infected, but non-contributing part of its existence.

Toxoplasma gondii, the parasite that causes toxoplasmosis, primarily harms humans through two main ways: by invading cells and tissues, causing direct damage, and forming tissue cysts in important areas. Most people who get infected show no symptoms, but in some cases, the parasite can invade specific organs and cause serious illness, especially in immunocompromised individuals. While cats are a significant contributor to the parasite's life cycle, humans can get infected through various means, including eating contaminated meat. The parasite can remain dormant in the body, but when the immune system is weakened, the cysts can reactivate and cause severe conditions like encephalitis.

Toxoplasmosis, a parasitic infection caused by the Toxoplasma gondii parasite, can lead to severe consequences when a pregnant woman is infected for the first time during her pregnancy. This condition, known as Congenital Toxoplasmosis, can result in various health issues for the fetus, including blindness, hydrocephalus, intracranial calcification, and seizures. The risk of infection and severity depend on the gestational age and the strain of the parasite. While there is treatment available, it primarily targets the rapidly dividing stage of the parasite and cannot directly affect tissue cysts. Screening for this condition is not routine in most places, and determining whether an infection is primary or past is done by looking for specific antibodies. The parasite has a written history of just over a century, and understanding its evolutionary history can provide further insights into its transmission and impact on human health.

In 1908, two researchers at the Pasteur Institute in Tunisia, Charles Nicol and Louis Manso, discovered Toxoplasma gondii in a rodent called a Gundi. At the same time, another researcher, Alfonso Splendor, discovered the same parasite in a rabbit in Brazil. However, it was Manso and Nicol who received the credit due to their findings being published in English, while Splendor's were in Portuguese and not translated until decades later. Toxoplasma gondii was not recognized as harmful to humans until 1938, when a case of congenital toxoplasmosis was identified in a newborn in New York City. The parasite can be transmitted through undercooked meat, but the definitive host was still unknown. In the 1960s, researchers conducted an experiment feeding raw lamb to people with tuberculosis to determine if they could transmit the parasite, but this did not answer the question of the definitive host. The discovery of Toxoplasma gondii and its impact on human health is a fascinating example of the importance of language in scientific research and the ongoing mysteries surrounding this parasite.

The discovery of Toxoplasma gondii in cats in the 1970s led to a better understanding of the complex life cycle of the parasite and its influence on rodent behavior. This discovery opened up a new field of research into behavioral manipulation of parasites and their impact on humans and microbes. The parasite's widespread presence can be attributed to the domestication of cats around 11,000 years ago with the rise of agricultural societies, which led to increased human-animal contact and the transmission of zoonotic diseases. The discovery of Toxo did not cause any major pandemics or dramatic cures, but it was a significant series of scientific findings that expanded our knowledge of parasitology.

The domestication of cats played a significant role in the shift of Toxoplasma gondii transmission patterns from the sylvatic cycle in forests to the domestic cycle involving house cats and house mice. This change led to the widespread prevalence of toxoplasmosis in humans and other animals, particularly in urban areas where the domestic cycle dominates. Cats were not initially domesticated primarily for rodent control, as they are less effective at reducing rodent populations compared to dogs. Instead, cats have been used for various purposes throughout history, from encouraging rain in Indonesia to being used in medieval tortures. Despite their limited effectiveness in controlling rodent populations, cats have become an integral part of human life and continue to hold various roles beyond pest control.

Cats have had a complex relationship with humans throughout history. From being revered as protectors and good luck charms to being seen as demons or agents of Satan, cats have accompanied humans on their journeys around the world. Along the way, they brought with them a parasite called Toxoplasma gondii, which is now found globally and poses a significant conservation and public health problem. Despite the issues caused by outdoor cats, many people love and cherish their feline companions. Solutions to mitigate the negative impact of cats on wildlife and ecosystems, such as trap-neuter-release programs, remain a contentious issue. In summary, cats have had a profound impact on human civilization and the natural world, and their relationship continues to evolve.

The issues surrounding outdoor cats and their impact on human and animal health are complex and contentious. Trap neuter release, a common method for controlling feral cat populations, is not effective due to the sheer number of cats and the effort required. Euthanasia, on the other hand, only permanently reduces population numbers if nearly all feral cats in an area are euthanized. The debate between these two approaches often overlooks the larger issue of how to address the presence of cats in the environment. Additionally, Toxoplasma gondii, a parasite found in cats, can have devastating effects on various animals, including kangaroos and sea otters, and may also impact human behavior and health, potentially leading to increased risk of schizophrenia. The relationship between Toxoplasma infection and human behavior is still a topic of research and debate, but it underscores the complex interplay between conservation, public health, and animal rights. Ultimately, finding a solution to the challenges posed by outdoor cats requires a nuanced and multifaceted approach.

While there is a correlation between toxoplasmosis infection and schizophrenia diagnoses, it is not a definitive cause-and-effect relationship. The vast majority of people with toxoplasmosis have not been diagnosed with schizophrenia, and there are people with schizophrenia who do not have the infection. Some antipsychotic medicines used for schizophrenia treatment may help stop the progress of the parasite, but this does not prove that toxoplasmosis causes schizophrenia. Additionally, there are geographic differences in toxoplasmosis prevalence, but the corresponding schizophrenia diagnosis rates do not always match. These studies are correlation studies, and it is unclear which condition came first. Some researchers have criticized the tentative links between toxoplasmosis and schizophrenia as building false hope. In the US, it is estimated that the annual cost of toxoplasmosis illness is $3,000,000,000 and 11,000 quality adjusted life years lost. Over 2,000 people develop eye disease from Toxoplasma in the US every year, and it is one of the three pathogens responsible for over 75% of all deaths due to foodborne illness in the United States. It is important to keep in mind that these statistics are specific to the US and that the cost and impact of toxoplasmosis can vary greatly in other countries.

Toxoplasmosis, a parasitic disease caused by T. Gondii, is a significant conservation and public health issue affecting a vast array of animal species, including humans. The parasite can persist in the environment, particularly in cat feces, leading to widespread contamination of soil and water. Cats, as definitive hosts, shed thousands of parasites during infection, contributing to the spread. While humans and other animals often show no symptoms, infection can be devastating for immunocompromised individuals and pregnant women. A One Health perspective, considering animal, wildlife, and environmental health together, is crucial for understanding and addressing the risks of toxoplasmosis. Strategies include soil studies, land use effects, understanding human behavior, congenital transmission research, wildlife and domestic animal cycle studies, food safety measures, outdoor cat monitoring, and vaccine development. Despite the availability of a vaccine for sheep, none exists for cats. The parasites can survive in water treatment processes and freezing temperatures, making water a significant source of infection. Toxoplasmosis remains a prevalent yet often overlooked threat to human and animal health. For further information, check out "The Lion in the Living Room" by Abigail Tucker and "This Is Your Brain on Parasites" by Catherine McAuliff, as well as articles by JP Dube.

The agricultural revolution marked a significant turning point in human history, leading to the formation of permanent settlements and the development of complex societies. This transformation was explored in a 2018 paper by Schwab et al, which provided valuable insights into human evolution and agricultural settlements. We encourage listeners to check out our website, thispodcastwillkillyou.com, for a list of all our sources related to this topic. We'd also like to extend our gratitude to Bloodmobile for providing the music for our podcast. And as a reminder, please keep your cats indoors for their safety, and don't forget to wash your hands to stay healthy. Thanks for tuning in!