The human brain is the most inaccessible place for pathogenic microorganisms. It is protected by the blood-brain barrier, which maintains homeostasis of the nervous system. Nevertheless, there are parasites that can bypass the defense, enter the brain and cause serious illness. "Lenta.ru" talks about eaters of nerve cells, worms in the head and microbes, suspected that they can even control human behavior.
Invisible killer
Fowler's amoeba (Naegleria fowleri) lives in warm freshwater lakes and slow-flowing rivers. Together with water, it can enter the nasal cavity of bathing children and young people, after which it finds a way to the brain along the nerves, where it causes a dangerous disease - primary amoebic meningoencephalitis. This rare disease most often (in 95 percent of cases) leads to painful death. A few days after infection, headache, dizziness, and fever occur. The patient's condition rapidly deteriorates, seizures, epileptic seizures, hallucinations begin. The patient loses his sense of smell, hearing or vision. Amoebas attack nerve cells, literally eating the human brain.
Amoebas are able to avoid the opposition of the human immune system. Once in the nose, they are fixed on the mucous membrane, from where they are introduced into the olfactory nerve leading directly to the brain. Once they reach the olfactory bulb (a structure in the lower frontal lobes of the brain), microorganisms begin to destroy nerve tissue. This leads to a loss of smell and taste about the fifth day after infection. The olfactory bulb serves as a springboard for the further spread of nigleria throughout the brain.
Amoebas affect the meninges. The immune system's response, which sends lymphocytes to fight infection, causes widespread inflammation. The patient has a severe headache, the neck becomes rigid, nausea and vomiting occur. However, immunity is unable to stop nongleria spreading through the central nervous system. Secondary symptoms appear: delusions, hallucinations, confusion, and seizures. The frontal lobes of the brain are most affected because they are located close to the olfactory bulb.
A person dies not due to the loss of nerve cells, but due to edema associated with the activity of lymphocytes, which increases the pressure in the skull. In the end, the connection between the brain and spinal cord is disrupted, and the patient dies from respiratory failure.
It takes a lot of water to get nonglerians in the upper respiratory tract. The risk group includes those who are engaged in water sports, diving or wakeboarding. A case of amoeba infection during a Baptist baptism has been described.
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Samples of nigleria
Amoebic meningoencephalitis has been diagnosed in only a few hundred people around the world. This disease was first described in 1965 in the Australian city of Adelaide. Later, cases of infection were recorded in the southern states of the United States, Europe, India, the countries of the Middle East and Asia. However, now Naegleria fowleri is found even in previously uncharacteristic regions - due to climate change.
In 2016, the Food and Drug Administration (FDA) approved the use of the drug miltefosine against amoebic infection - after several children were able to treat meningoencephalitis with it.
Brain worm
Much more common is a parasitic infection of the brain caused by the ingress of cysticercus - larvae of the tapeworm pork tapeworm (Taenia solium) into the central nervous system. The US National Institutes of Health classifies neurocysticercosis as the leading cause of epilepsy worldwide. According to the WHO, more than 50 million people are now infected with tapeworms, and in the United States alone, about two thousand new cases of neurocysticercosis are recorded annually.
Tapeworm larvae penetrate the human brain after the eggs of helminths enter the gastrointestinal tract. An egg is a bubble that is the size of a walnut. In the stomach, its membrane dissolves, the larva penetrates into the intestinal walls and spreads through the body through the blood vessels. In more than half of cases, cysticercus is brought into the central nervous system.
Cysticercus can be located in the cavity of the ventricles, where it floats freely in the cerebrospinal fluid, in the pia mater or in the cerebral cortex. The presence of the worm causes chronic inflammation and toxic effects on the central nervous system. The patient may experience paresis or paralysis of the limbs, severe headaches, speech impairment, epileptic seizures, and even changes in the psyche.
A person can live peacefully for decades, not knowing that a parasite has settled in his head. This is due to the fact that the worm, apparently, produces substances that suppress the immune response. But sooner or later the pork tapeworm dies, turning into a calcified corpse. Immunity strikes back immediately, leading to neurological symptoms.
Pork tapeworm
Neurocysticercosis is common in Asia, Central Africa and Latin America. It is believed that in some regions up to 25 percent of the population is infected with pork tapeworm. In 2015, tapeworms killed about 400 people worldwide.
Most often, parasite eggs enter the human body through dirty water and unwashed vegetables, as well as through eating raw meat.
Zombie parasite
Toxoplasma is a protist, the owners of which are mainly cats. However, people also become infected with it, which, however, in most cases does not threaten anything special. Toxoplasma is dangerous only for pregnant women and people with reduced immunity. At the same time, a number of scientists believe that protists can also influence human behavior, almost forcing him to start cats.
It has been proven that mice infected with the microorganism are less afraid of representatives of the feline family. As a result, such rodents often become victims of domestic animals, and protists successfully penetrate the body of their main hosts. A similar mechanism has been proposed for humans by biologist Kevin D. Lafferty at the University of California, Santa Barbara. The scientist found that in those regions where a significant part of the population is infected with Toxoplasma, neuroticism is also common, which affects the development of culture. It should be noted that this correlation does not indicate a causal relationship. Therefore, the assumption about the influence of parasites on human behavior remains an unconfirmed hypothesis, despite its popularity.