Toxoplasma gondii is an obligate intracellular, parasitic protozoan that causes the disease toxoplasmosis. Diagram of Toxoplasma structure.
Image Credit: Designua / Shutterstock
In my last blogpost, I described how the parasitic organism, cryptosporidium, is one of those 'irreducibly complex' organisms that creationists have been fooled by Michael J Behe into believing are proof of their putative creator god, because, so their ignorant intuition tells them, there can only be one intelligent designer capable of designing an irreducibly complex structure such as the bacterial flagellum or the apical complex structure that all members of the Apicomplex phylum characteristically possess.
Sadly for them, though, their reliance on this 'proof' of their god precludes them from arguing that these nasty little pathogens that appear to be designed to make us and other animals sick is the work of another intelligent creator, 'Sin', so the inescapable conclusion must be that their beloved creator god is designing these pathogens to make us sick and to increase the suffering in the world.
As though that wasn't bad enough, we now have another related parasite, also a member of the Apicomplex phylum, that on the face of it, seems to be an even more determined attempt to make us sick. It's a parasite that once you have it, you have it for life, and the evidence is that it manipulates your behaviour and changes your personality too. This then raises doubts about the idea of free will that is a central part of creationist superstition, and notions of 'Original Sin' (that thing that can supposedly create parasites too).
This organism is Toxoplasma gondii which is carried by about 25% of the world's people, so the chance of you or me or any of your friends and family having it is quite high.
Tell me all about Toxoplasma, its evolutionary relationship to other protozoan parasites and what it does to its victims, including humans. Toxoplasma gondii:Toxoplasma gondii can infect many different mammals but to breed successfully, it needs to infect a member of the cat family, including the domestic cat. It sheds its eggs into the cat's intestine, so they are excreted in cat poo. But, to complete its life-cycle it needs to infect another host then get back into a cat, and this is where the any 'designer' of Toxoplasma gondii got really devious and, apparently had no regard for the welfare of this secondary host.Understanding the evolutionary relationships, life cycle, and host interactions of Toxoplasma gondii is crucial for developing effective prevention strategies and treatment options. Research continues to explore the complex biology of this parasite and its impact on both animal and human health.
- Evolutionary Relationship:
- Toxoplasma gondii is a protozoan parasite belonging to the phylum Apicomplexa.
- Evolutionarily, it is related to other important parasites within the phylum, including Plasmodium (causative agent of malaria) and Cryptosporidium (causative agent of cryptosporidiosis).
- The apicomplexans share a common ancestor and are characterized by the presence of an apical complex, a specialized structure involved in host cell invasion.
- Life Cycle:
- Toxoplasma has a complex life cycle involving both sexual and asexual stages.
- The primary hosts are members of the Felidae family, such as domestic cats, where sexual reproduction occurs in the intestinal epithelial cells.
- Asexual reproduction occurs in a variety of warm-blooded animals, including humans, who can become intermediate hosts.
- Transmission:
- Cats shed oocysts (eggs) in their feces, and these oocysts can contaminate the environment, leading to the infection of other animals and humans through ingestion of contaminated food, water, or soil.
- Consumption of undercooked or raw meat containing tissue cysts is another common route of transmission.
- Clinical Manifestations:
- In healthy individuals, Toxoplasma infection may be asymptomatic or result in mild flu-like symptoms.
- However, the infection can have serious consequences for certain groups, such as:
- Pregnant Women: Infection during pregnancy can lead to congenital toxoplasmosis, potentially causing severe birth defects or fetal death.
- Immunocompromised Individuals: Those with weakened immune systems (e.g., HIV/AIDS patients, organ transplant recipients) are at risk of developing severe and disseminated disease.
- Tissue Cyst Formation:
- After infection, Toxoplasma forms tissue cysts, commonly in the brain and muscle tissues.
- The ability of Toxoplasma to encyst and persist in host tissues contributes to its long-term survival and potential for reactivation in immunocompromised individuals.
- Manipulation of Host Behavior:
- One of the intriguing aspects of Toxoplasma is its potential to manipulate the behavior of its intermediate hosts.
- Studies in rodents have suggested that Toxoplasma infection can alter the behavior of infected rodents, making them less fearful of predators, potentially increasing the likelihood of predation by cats.
- Diagnosis and Treatment:
- Diagnosis is often based on serological tests to detect antibodies or molecular methods to identify the parasite's DNA.
- Treatment with medications such as pyrimethamine and sulfadiazine is available, particularly for severe cases.
The parasite infects the brain and manipulates the behaviour of the host to increase its chances of being eaten by a cat. The secondary host is literally sacrificed to produce more copies of the parasite!
If the secondary host is a rat or a mouse, they lose their instinctive fear of cats; if the secondary host is a chimpanzee, they develop a fondness for the smell of leopard urine. Possibly as an echo of the manipulation of a common ancestor of humans and chimpanzees, toxoplasmosis (the disease caused by Toxoplasma gondii) has been shown to change a person's behaviour too, as explained in the following article by Justyna Anna Nalepa-Grajcar a PhD Researcher at Aberystwyth University, Wales. Her article is reprinted from The Conversation under a Creative Commons license, reformatted for stylistic consistency:
Toxoplasma ‘cat poo’ parasite infects billions – so why is it so hard to study?
Justyna Anna Nalepa-Grajcar, Aberystwyth University
What if I told you that there is a good chance you are carrying a parasite that is transmitted through cat poo? Two billion people around the world carry Toxoplasma gondii so there may be more than a 25% chance that it is in your body too.
Toxoplasma is closely related to Plasmodium, the parasite that causes malaria. But while Plasmodium is quite fussy about where it lives, only able to survive in liver cells and then in red blood cells, Toxoplasma doesn’t much care. It muscles its way into just about any type of cell.
But it’s also very hard to isolate Toxoplasma from the cells that it infects. So I’m trying to find a method to increase the amount of Toxoplasma parasite in samples. This will allow scientists to have better quality samples to investigate how the parasite spreads and look for ways to treat it.
In some parts of Europe, such as France, around 50% of the population play host to the parasite. Once infected, you will never get rid of your new silent buddy. But humans are not actually the parasite’s natural host. Normally it cycles between cats – both domestic and wild – and the animals they eat.
It’s not only through cat faeces that humans can become infected, however. In fact, the most common method of infection is through consuming undercooked or rare meat containing the parasite. Infection can also happen in the womb, or through an organ transplant from an infected person.
At worst, a typical Toxoplasma infection (known as toxoplasmosis) feels like a light flu. The parasite doesn’t want to kill its intermediate host (us) after all. It’s only when the oocyst begins to falter – when it can no longer get into its final host – that it become dangerous.
It can be particularly dangerous for a woman to get toxoplasmosis during pregnancy. A developing infant is protected only by its mothers’ antibodies that cross the placenta. But the mother’s T cells (the body’s most effective weapons against bacteria and parasites) can’t cross into the foetus. This is because T cells would act as if the developing child were a huge parasite and destroy it.
Maternal antibodies do a good job against a flu virus, but can’t protect against Toxoplasma. For Toxoplasma, the foetus would need its own inflammatory T cells to drive the parasites back into their oocysts. But foetuses don’t have their own T cells either. So if the parasite managed to pass from mother to baby it would reproduce widely and multiply until it caused brain damage.
Investigating effects
Due to this unique behaviour, Toxoplasma has been widely investigated by parasitologists, biologists and psychiatrists. Researchers have found that the Toxoplasma parasites may affect human behaviour and personality, for example. Studies have also suggested a link with schizophrenia and bipolar disorder.
Further research has also shown that infected men have a tendency to disregard rules, and that they are more suspicious and jealous. In women, the shift in these two factors is the opposite. They appear to be more warm-hearted, outgoing and easygoing than women without the parasite.
Another study found that students infected with Toxoplasma were 40% more likely to major in business at university, and 70% more likely to emphasise “management and entrepreneurship” in their business studies.
While scientists are currently trying to find out more about how the parasite affects people, however, they face a critical problem. It is very difficult to isolate Toxoplasma from human DNA, and the parasite can only grow within other living cells. So unlike bacteria, it cannot be easily cultured in the lab.
In addition, unlike many other disease-causing microbes, Toxoplasma is typically found in very low numbers within clinical samples. So when a sample is purified, the vast majority of DNA in it will come from the patient rather than the parasite.
My current research is focused on increasing the number of parasites to obtain high quality samples. It might seem counter-intuitive to try to increase the amount of parasites, but it is important that we get a large number of them in different samples for comparison. To amplify the target Toxoplasma’s DNA, I am using a new technique called selective whole genome amplification to increase the number of parasites in a sample more than 100 times.
My ultimate aim is to analyse the parasite’s DNA and compare samples found in the UK with samples from across Europe and around the world. This will hopefully shed light on what the common sources of infection are in the UK population, and improve our understanding of the epidemiology and virulence of this important human pathogen. And will assist in developing new treatments, methods of surveillance and strategies to stop people getting infected.
Justyna Anna Nalepa-Grajcar, PhD Researcher, Aberystwyth University
This article is republished from The Conversation under a Creative Commons license. Read the original article.
But what Creationists need to explain, apart from the evidence of malevolent design, if you believe this complex organism must have been designed and couldn't have evolved, is why would a god who supposedly handed down rules for humans to live by, then go to the trouble of designing a parasite that changes their behaviour to make them less inclined to obey those rules?
And, if a parasitic organism can make us take decisions we wouldn't otherwise take, how is that consistent with the idea of free will on which the notion of 'Original Sin' is predicated?
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