Parasite is a term derived from the Greek language and means eating at the table of another. It hits the nail on the head, because in modern understanding every parasite lives at the expense of its host.
Parasitic diseases (parasitoses) are caused by parasites that have entered the body. Symptoms of diseases may appear immediately after contact with the parasite or after an incubation period, which may take various lengths. Parasitosis may self-heal, become chronic (often without symptoms) or, in extreme cases, lead to the death of the host. Most parasitic diseases do not have a so-called characteristic diagnostic features. Therefore, their diagnosis must be based on the analysis of all symptoms and differentiate them from those present in other diseases.
Paths of infection and penetration of parasites
Parasites and pathogenic microorganisms can enter the human body through the digestive tract, respiratory tract (inhalation, inhalation), sexually, through the damaged oral mucosa, skin, through the conjunctiva and the cornea, and into the fetus as a result of intrauterine infection. The place of penetration of parasites (the so-called invasion gate) are also natural openings, i.e. the oral cavity, nose, urethra, vagina and anus. Here are some examples.
Armed tapeworm – enters the body after eating infected, undercooked or raw pork. Signs of infection may include diarrhea, nausea, loss of appetite or stomach pain. However, infection is usually asymptomatic.
Unarmed tapeworm – the cause of infection may be eating raw or undercooked (undercooked) beef meat with encapsulated tapeworm larvae. The symptom is abdominal pain, worsening when we are hungry, vomiting, weight loss, nausea.
Human roundworm – the source of infection may be soil, water, so by drinking unboiled water, we introduce the parasite larvae into the body. The same happens when we eat unwashed, raw vegetables and fruits. Infection with roundworm is manifested by dizziness, increased nervous excitability, skin changes, diarrhea or constipation.
Pinworm – penetrates through the alimentary or inhalation route. Food, furniture, bedding and the air in the apartment can be contaminated. The symptoms of infection are itching of the anus and red skin in its vicinity, lack of appetite, weakness, lack of concentration, headaches and stomachaches.
Spiral (tortuous) hair – infection is transmitted after eating meat or meat products that contained the larvae of the parasite, and before eating it was not subjected to appropriate heat treatment. The symptom will be a flu-like condition, stomach aches, headaches and even heart aches.
Harm to the body
Different parasites can affect the host in different ways. The harmful effects of parasites may take the form of mechanical damage, toxic effects or overeating the host from food.
Large, in relation to the habitat, parasites may cause small intestine obstruction. Parasites equipped with a sticking apparatus can damage the host’s tissues. And so the lamblia clinging disc, furrows of the broad mite, suckers and hooks of the armed tapeworm can cause changes in the small intestine, strongly muscular flukes – in the bile ducts, and cloves in the hookworm’s mouth – in the duodenum. The intestines can also be damaged during the migration of parasites. Pressure on the internal organs can cause their malfunction, which can occur after infection with echinococcosis, which can increase its size up to 10 cm in diameter.
Parasites living in the digestive tract eat their host from undigested food or decomposed food components. Parasites not only use proteins, carbohydrates and fats, but also absorb enzymes, vitamins and hormones. This has a negative impact on human health.
The toxic effect of parasites on the human body is related to the fact that they produce many enzymes that damage cells and inhibit physiological processes. Some protozoa are haemolytic, which may lead to blood clotting disorders. The products of metabolism or protein breakdown products of the parasites themselves also have a toxic effect on the human body. Flukes secrete organic acids and fats, tapeworms secrete organic acids and nitrogen compounds, and nematodes only nitrogen compounds. These compounds can provoke degenerative changes in some organs, such as the liver or kidneys. Many parasites produce substances (e.g. histamine, acetylcholine) that cause inflammation, dilate blood vessels, destroy the lining of the gut, which can lead to ulceration. Ticks release particularly strong toxins, which can result in cerebral palsy.
Some parasitoses, or parasitic diseases, are accompanied by symptoms resembling an allergy. Skin reactions, catarrh of the upper respiratory tract and bronchial asthma are an expression of the organism’s hypersensitivity to parasite antigens. Upper respiratory tract infections and bronchial asthma are caused by house dust mite allergens. But bronchial asthma attacks can also be caused by lice faeces, air inhalation of body parts and secretions of houseflies, bedbug antigens or other arthropods.
Defense strategy
Parasites can enter the human body in many ways. But our organism, although imperfectly, also defends itself against their invasion. The outer protective barrier is the skin, respiratory mucosa and conjunctiva. Cilia and mucus on the oral mucosa protect us from parasites that want to enter the body this way. Many intruders are also barred from tears, saliva and body fluids. The most important fighter, however, is the immune system. Its reaction is determined by the site of infection and the type of parasite.
During the invasion of worms, both the elements of the non-specific and specific immune response are activated. Macrophages and monocytes phagocytose (devour) parasite antigens, then attach fragments of these antigens to histocompatibility molecules and present specific epitopes (fragments) of the parasite to lymphocytes. In this way, phagocytes (phagocytes) as units of the non-specific reaction mediate the shaping of the specific response. At the same time, they produce cytokines and chemokines that enhance and localize the antigenic impulse. Other food cells such as neutrophils (cells of the immune system) and eosinophils (a type of white blood cell) get involved in the reaction. An immune reaction and inflammation develop. It is the body’s first line of defense, the effectiveness of which is determined by genetic factors.
An allergic immune reaction is responsible for the elimination of intestinal nematodes, while the cellular response has been assigned a protective function directed mainly against the larvae of flukes and tapeworms.
Disease symptoms caused by tissue parasites are similar to those that characterize an allergy. Both are characterized by a higher frequency of Th2 helper responses and increased levels of IgE. The geographical distribution of helminthiasis and allergic diseases is complementary and not coexisting. Some work suggests that immune mechanisms that reduce the response to worm infection may be of benefit to the host by blocking the induction of atopic reactions. But the results of the studies conducted so far on the effects of parasitic infestation on the incidence of asthma are inconsistent, and it is currently difficult to assess whether or not the infection reduces or increases the risk of asthma.
Tekst: Anna Jarosz