Once someone in the family is pregnant, then the pet cat will often become the first victim and be abandoned, so the cat is often jokingly called "if you have a child, you don't want me".
The main reason is that people are afraid that the toxoplasmosis that pet cats may carry will be transmitted to unborn children.
Toxoplasma gondii is probably one of the most widespread known parasites in the world, they can parasitize almost all warm-blooded animals, for birds, all but one mallard duck has been found to be infected with Toxoplasma gondii, and mammals are the same, all mammals from sea to land have been found to be infected, for humans, there may be at least 2 billion people infected with Toxoplasma gondii (up to 50% of people may be infected).
Toxoplasma ©Dr_Microbe
Toxoplasma gondii may also be one of the most mysterious and interesting parasites, as they have been observed to influence host behavior, and our understanding of them is still very limited.
So what kind of parasite is Toxoplasma gondii, why can they spread so unscrupulously, and do we have a way to deal with it now?
How is Toxoplasma transmitted?
In fact, abandoning the cat until you are pregnant is undoubtedly self-deception, because it is never the cat that transmits Toxoplasma to the fetus, but the mother herself is a carrier of Toxoplasma - the only way for Toxoplasma to be "transmitted from person to person" is the placenta.
We humans, and most other warm-blooded animals, are only intermediate hosts for Toxoplasma gondii, and their ultimate host is felines – 17 species of cats have been found to be the ultimate hosts of Toxoplasma gondii, including our pet cats.
Toxoplasma gondii reproduces sexually only in cats, while in all other warm-blooded animals considered intermediate hosts, toxoplasma only reproduces asexually.
Toxoplasma gondii is a protozoan whose main way of survival is parasitism.
The main closed loop of their parasitism is: cats eat the intermediate host carrying Toxoplasma gondii, and then they complete sexual reproduction in the feline, excrete it in the form of oocysts, and then be ingested by the intermediate host and transmitted to the cat, so as to cycle.
The oocysts of Toxoplasma gondii are thick walls that wrap fertilized eggs, and their survival ability is relatively tenacious, in those soil, water, fruits and vegetables contaminated with feline feces... Oocysts can survive for months (even in seawater for 6 months) until ingested by an intermediate host or other feline.
The initial experience of the oocyst of Toxoplasma gondii into the feline family and the intermediate host is basically the same, in that the cyst wall is dissolved by proteolytic enzymes in the stomach and small intestine and releases sporozoites, and then begins to invade nearby cells.
However, the cats, which are the final hosts, are significantly less sensitive to Toxoplasma oocysts and are more easily parasitic to complete the initial parasitism.
When a new host cell is just invaded, their activity is very active and reproduces very quickly, so this stage is called tachyzoites.
Toxoplasma infection is divided into three stages, tachyzoites are the first stage of toxoplasmosis infection, in which Toxoplasma produces specialized vacuoles in the host cell membrane – called parasitic vacuoles – that completely envelop themselves and rapidly replicate themselves inside until the host cell dies and releases tachyzoites, which then circulate through the bloodstream to all tissues and organs, including the brain.
Figure: Synzoite split
As tachyzoites spread, our immune system can no longer sit still, at which point the immune response becomes very strong, and sometimes the host (human) has a high fever.
At this time, Toxoplasma gondii also has a very intelligent survival strategy, they will not be directly positive with our immune system, but enter the second stage - bradyzoites.
In the bradyzoite stage, they form clusters of cysts in our tissue cells - called cysts, which are also wrapped in bubble membranes, a bit like adding stealth to avoid being cleared by the immune system.
Figure: Tardyzoites in mouse tissues
The proliferation rate of retardation is very slow, so in the host and the host peaceful coexistence, as long as the immune system is normal, the host is basically not likely to have problems.
It's worth mentioning that while bradyzoites can parasitize within any tissue, their favorite places are the brain, eyes, and rhabdomyotes (including the heart) – firmly grasping the most important organs of the host owner.
Ingestion of cysts and oocysts may infect warm-blooded animals with Toxoplasma gondii, which is mainly found in water and soil, and contaminates some vegetarian vegetables and grasses, while cysts are present in intermediate hosts, and may be infected as long as they eat undercooked meat.
If cats ingest both, Toxoplasma gondii develops sexually in its body and produces the third stage of Toxoplasma gondii, oocysts, while all other intermediate hosts do not.
The variety of transmission methods and the parasitic strategy of "not harming" the host may be the reason why Toxoplasma gondii has become the "first brother" in the parasite world.
Mice whose behavior is controlled by Toxoplasma gondii
As we mentioned earlier, one of the favorite places for Toxoplasma gondii to parasitize is the brain of the host, so it is indeed possible for Toxoplasma to influence the host's behavior to some extent, and manipulating the host must also be evolutionary for Toxoplasmosis.
Since felines are the only ultimate hosts of Toxoplasma gondii, what they want to do most is definitely infect more cats to complete efficient gene transmission.
Felines are the top predators, and cysts are an important mode of transmission of Toxoplasmosis, as long as Toxoplasma controls the host a little, making it easier for cats to eat the host carrying cysts, they are actually easy to achieve greater success.
Many studies now find that basically conform to this speculation - Toxoplasma gondii will make intermediate hosts easier to be eaten by cats.
图源：Wendy Ingram/Adrienne Greene
In studies on rats, rats infected with Toxoplasma gondii had a reduced aversion to cat urine and at the same time developed X excitement about cat odor.
However, in studies of mice, no unique selection for cats was found, but rather that mice infected with Toxoplasma gondii reduced anxiety and increased exploratory behavior, while general loss of aversion to all predators.
Whether it is a single choice for cats or a universal choice, infection with Toxoplasma gondii will make intermediate hosts easier to eat in some way, which is basically certain.
The possible impact of Toxoplasma gondii on us has also been found in some human studies, including that the risk of traffic accidents in people infected with Toxoplasma gondii is 2.65 times higher than that of ordinary people, the history of mania and depression is 2.4 times higher than that of ordinary people, and the situation of choosing to start their own business is 1.8 times higher than that of ordinary people.
In fact, there are many related studies, which can be summarized as Toxoplasma will reduce the obedience of the host, while increasing behaviors such as irritability and exploration, and significantly increase mental disorders (such as schizophrenia).
However, the effects of Toxoplasma gondii on humans are still considered non-mainstream and lack evidence, so just take a look and don't be too real.
Although the effects of Toxoplasma infection on human behavior (if they exist) are not necessarily entirely negative, this thing is 100% thunder in the body.
Source: SamKakeru/Fruit Shell
Long-term presence of Toxoplasma gondii in the form of cysts does not pose any health risks to people with normal immune systems, but once there is a problem with the immune system, it can be fatal for infected people.
Because the baby's immune system is relatively weak, Toxoplasma gondii does have a greater impact on the baby, and it is understandable that some people do not touch cats after pregnancy.
So, is there a cure for Toxoplasma infection?
Human drugs (antibiotics, etc.) can easily kill Toxoplasmosis, so acute infections are well treated, but cysts cannot be completely removed, as long as Toxoplasma forms cysts in tissue cells, it will accompany the host for a lifetime.