Parasitology is the science that studies parasitic phenomena. The main task of this branch of science is to study the relationship between the parasite and the host, their influence on each other, which also depends on environmental factors.
Due to the increase in the migrant population (the growth of tourism, due to the increase in the number of people arriving from different countries), the role of parasitology in the health care of the modern worldhas increased many times. Next let's look at what types of parasites can live in the human body and what symptoms can arise from different types of infections.
The number of immunocompromised people is increasing, including HIV-infected patients, and also due to advances in medicine related to the use of chemotherapy and the development of transplantation.
All this leads to the fact that most diseases (infections) caused by parasites, which often occur without complications or without any symptoms, can be fatal in people withweakened immune system.
The response to the appearance of parasitic organisms in these patients differs greatly from the usual response, leading to the appearance of acute, atypical forms of the disease.
In addition, human activity causes global changes in climatic conditions and natural landscapes, leading to the spread of disease vectors from endemic areas to other areas and regions.
Medical parasitology is divided into several sections depending on whether the parasitic organisms belong to different groups: protozoan parasites, helminth parasites, parasitic arthropods, etc. v. So, science is divided into:
- Medical protozoa (study of parasitic protozoa, symptoms and treatment of protozoa);
- Medical helminths (study of parasitic helminths, symptoms and treatment of helminth infections);
- Parasitic entomology (study of parasitic arthropods).
Relationships between organisms
Parasitism is a special way of relationships between organisms of different species, in which one of them (parasite) uses the other (host) as a permanent or temporary habitat, and at the same timetime as a food source.
Parasites do not kill the host immediately but must eat the host many times. During the process of evolution, parasites have developed special mechanisms of interaction with their hosts, ensuring the survival of all parasitic species.
External natural conditions affect the parasite not directly but indirectly through the host.
Parasitic phenomena are quite common on the planet. Parasites can belong to any systematic group of all biological kingdoms. Any type of organism except viruses can become a "home" for parasites.
In this case, the parasitic individuals themselves become hosts for parasites of other taxonomic groups of animals.
Parasitocenosis is the total number of all parasitic organisms living simultaneously in the host. Pathogens are parasitic organisms that are specific to different host species.
Parasites that live inside their hosts not only feed, but also cause various diseases that can lead to the death of the affected person. This phenomenon is called pathogenicity.
Parasites in the human body have a negative impact on it through several mechanisms:
- Cell and tissue damage;
- Impact on the host's immune defense mechanism and antibody production;
- Sensitivity of the host organism (hypersensitivity);
- Toxic effects of metabolic products of parasites.
The development cycle of a parasite is the total number of morphological stages of development of the organism, and is also an indication of the living environment of each stage, the route of infection and transmission.
For example, the following stages are distinguished in the development of parasitic worms: invasive stage – penetration into the host body; stage of larval formation; adult stage, sexual maturity.
Invasive (infectious) diseases are diseases caused by parasitic organisms. Invasive diseases in humans are divided into protozoa (caused by protozoa), helminths (parasitic worms), and diseases caused by parasitic animals.
Signs of parasites in the human body are so diverse that it makes no sense to consider them as a whole. So next we will look at the symptoms of primary protozoa, helminthiasis, and invasions caused by other animal organisms.
Due to the need to adhere to a parasitic lifestyle, three types of parasites are distinguished:
- False parasites. Accidental entry of a free-living individual into a host, which may persist for some time and is capable of disrupting the normal processes of its life. Pseudoparasites are soon released into the environment (e. g. through feces) or die after a short period of time. Pseudoparasites inherent in some species of leeches accidentally enter the human nasal cavity, where they live and cause bleeding, mites and their eggs enter the stomach and are excreted in feces, and anumber of amoeba species.
- Facultative parasitism is the ability of an organism to live both with and without a host. The viability of the parasite lasts longer in the first case. This type is characteristic of fly larvae that have the ability to develop outside a living body and when accidentally entering that body (causing agent of mycoses).
- True parasitism. This type of parasite includes worms, fleas, lice, etc. v.
| Related to the host's body | |
|---|---|
| Parasites | They live on the integumentary surface, feeding on blood cells and the upper layers of the skin. |
| Endoparasites | They live inside the host's tissues, cells, and cavities. They may only be located in one of the organs, but can move to nearby organs, causing damage at the same time. |
| According to exposure time | |
| Temporary parasites | Usually they are parasites; Their exposure is usually short-lived |
| Fixed parasites | For such parasites, the host is also a kind of "home". This method of parasitic life is divided into two types: periodic (the parasite spends part of the time in the host) and permanent. |
| According to specificity | |
| Multi-specific | Able to change to different types of hosts, as they feed on blood, epidermis and other tissues inherent in many types of living organisms |
| Single substance | Can only parasitize certain host species (species). |
Owner concept
The host is a living organism that the parasite uses as a source of nutrition and a place to live. Most parasitic individuals can change hosts, this is due to the presence of several stages in the life cycle of the parasite.
The definitive host (otherwise primary, last, final) is an organism where the parasite lives in its adult stage and can reproduce sexually.
An intermediate host is a host in which the larval stage of the parasite lives or the stage only reproduces asexually.
Reservoir - inside which the parasite can survive, increase in number but do not mature further.
Parasitic diseases can be humanoses (source and host are humans), humanzoonoses (source and host are both humans and animals) and zoonoses (source and host are animals). object).
Many infections are so-called naturally endemic, when pathogens move among wild animals in a given area.
Methods of diagnosing parasitic infections
You cannot get rid of "parasites in the body" with "miracle pills" or folk remedies, you can cause even greater damage to yourself. First, you need to understand what type of aggression a person has. To diagnose invasive diseases, macroscopic, microscopic and immunological methods are used.
Macroscopic techniques help identify infectious agents on the external surface or in the stool of the affected person.
Microscopic methods also help identify parasites in blood smears, tissue fluids, muscle tissue biopsies, as well as in sputum, stool, gastric and duodenal gastric juices.
In the study of parasites, optical and electron microscopic methods using light and electron microscopes are used. Here, diagnosis is based first of all on a deep knowledge of the morphological structure of the infectious agent, methods of preparation, fixation and staining of smear preparations.
The results of microscopy depend on the choice of pathological materials, their properties, the time of collection from the appearance of symptoms and the time of examination from the moment of receipt of the materials.
Immunodiagnostic methods include serum and allergic reactions. Serological tests are used for:
- Identify microbial strains, toxins, and antigens using immunodiagnostic serum;
- To determine the nature of antibodies in serum using diagnostic antigens.
The basic serum reactions are agglutination, precipitation, lysis, complement binding, neutralization and other reactions. Methods using labeled antibodies are also known: immunofluorescence, enzyme-linked immunosorbent assay, immunoassay, radioimmunoassay.
Nucleic acid hybridization and polymerase chain reaction methods have been widely used in diagnosis.
Issues of prevention and anti-epidemic measures
Preventive measures for all parasitic diseases can be summarized as follows:
- It is necessary to protect soil and water sources from contamination by human and animal feces.
- Residential areas and toilets need to be improved.
- It is necessary to carry out sanitary monitoring of territories and water supply to residential areas, as well as the production, transportation and sale of food products.
- It is important to carry out veterinary and hygiene surveillance at slaughterhouses, meat processing plants, markets and livestock farms.
- It is necessary to identify and treat carriers of the disease.
- There is a need to protect humans from harm by arthropods and to increase knowledge about personal prevention of parasitic diseases.
Anti-epidemic measures include proactive detection of infected people and carriers, registration and treatment of infected people, hospitalization and medical examination if necessary, neutralization or destruction of sources of infection. Personal prevention is of great importance: hygiene measures, annual medical examinations, proper preparation for travel, addressing the issue of prophylactic treatment.
Chemoprophylaxis, i. e. the use of antihelminthic drugs in risk groups and endemic areas once or twice a year, was developed by WHO for disadvantaged and developing countries.
General characteristics of protozoa
Protozoa are single-celled organisms with a nucleus (eukaryotes).
No more than a millimeter in size, they are found everywhere and in every corner of the planet. Parasitic protozoa are also divided into ectoparasites and endoparasites.
Characteristics of protozoa:
- The body is made up of one cell, which performs the functions of both the cell and the entire body. Body shape can be diverse: variable, elongated or spindle-shaped.
- Some protozoa are covered only by cell membranes, while others have elastic membranes called granules.
- The cytoplasm of the cell is divided into: dense outer (ectoplasm) and inner (endoplasm). The cytoplasm may contain one or more nuclei.
- Nutrients enter in different ways: through pinocytosis (absorption), phagocytosis (active ingestion), osmosis (ingestion of substances due to concentration differences), active transit throughmembrane.
- Gas exchange occurs throughout the cell due to the osmotic component. Waste products are also released from the entire cell surface and with the help of digestive vacuoles.
- Single-celled organisms reproduce both sexually and asexually.
- Unicellular organisms have a variety of locomotion mechanisms: pseudopods, flagella, and cilia. They can respond to stimuli due to photo, chemotaxis and thermoregulation and other mechanisms.
- In poor conditions, parasitic protozoa turn into cysts, that is, they are covered with a dense layer of cysts. In the cystic state, life processes stop.
Under favorable conditions, the cyst sheds its shell and turns into a vegetative form, continuing an active life.
Detection of parasitic protozoa in material from patients presents virtually no difficulty. Typically, one will examine a stain and a thick drop of blood.
Stools are usually examined fresh using a heated table. To detect amoebic cysts, Lugol's solution is added to the stool, staining the internal structures.
At this time, all protozoa were classified into the kingdom Protista, which included seven types, of which only three were of medical importance.
Subspecies Sarcodae
The shape of Sarcodidae cells varies; The cell membrane forms protrusions, which can then return to their original form, called pseudopods.
Thanks to them, cells move. Sarcodidae live absolutely everywhere: land, fresh water, sea. Infectious diseases caused by Sarcodidae are common worldwide, but are more commonly found in tropical and subtropical regions.
Sarcode amoebiasis most commonly affects the human digestive system; These are intestinal parasites. Free-living amoebas of other orders also cause serious infections if accidentally swallowed and settle in the human body.
To diagnose amoebiasis, microscopic examination of stool is used. They contain vegetative or cystic forms of sarcode. When examining fecal preparations with a special heated table, it is possible to detect amoeba pseudopods and their forward movement.
To treat amoebiasis, people use drugs divided into groups: contact, acting on life forms in the intestinal lumen, and systemic tissue amebicides, acting on amoebas that have penetrated the intestinal tissue andother agencies.
In addition to treatment, liver abscess aspiration is performed if chemotherapy is ineffective or there is a risk of abscess rupture. The table below describes the major parasitic protozoa of the Sarcodidae subgroup.
Subphylum whip
Representatives of the flagellum subgroup, in addition to the cytoplasmic membrane, also have a granule (such a shell gives a constant shape) and flagellum (one or more).
Flagellum contains contractile fibers that allow it to move. Some representatives of the flagellum have an undulating membrane, inside which the flagellum/flag is located without exceeding its limits.
Flagellum begins at the kinetosome, which stores energy. Inside some flags there is an axostyle - a dense rope inside the body that provides support.
The main symptoms and signs of infection of representatives of the flagellate subgroup are presented in the table below.
| Representation/Localization | Symptom | Diagnose |
|---|---|---|
| Giardia (Lamblia intestinalis or Giardia lamblia) / Duodenum and small intestine | Nausea, heartburn, abdominal pain, bloating, heartburn, diarrhea, body intoxication, exhaustion | Microscopy of duodenal contents, stool examination, ELISA for Giardia antibodies |
| Intestinal Trichomonas (Trichomonas hominis/intestinalis)/ Small intestine, large intestine | Colitis, enteritis, cholecystitis, diarrhea | Detection of vegetative forms and cysts in patients' loose stools |
| Trichomonas vaginalis (Trichomonas vaginalis) / Vagina, cervical canal, urethra - in women. Urethra, prostate, testicles - in men | Colitis, urethritis in women, itching, burning in the genital area, vaginal secretion of yellow foam. Asymptomatic gonorrhea, urethritis, prostatitis in men | Vaginal secretions in women, urethral and prostatic secretions in men, PCR, culture |
| Oral Trichomonas (Trichomonas tenax)/ Oral cavity, respiratory tract, tonsils, gums | Tooth decay, periodontal disease, ear, nose and throat disease | Imprint and cultural stains |
| African trypanosomes (Trypanosoma brucei gambiense and Trypanosoma brucei rhodesiense)/ Skin at the site of penetration, lymph nodes in the neck and back of the head, blood vessels | Fever, lymph node pain, skin rash, headache, drowsiness, tremors, paralysis, slurred speech, coma, seizures, exhaustion, acute heart failure, death | Check the bite site and biopsy the lymph nodes. Blood smear and solid drop method, Wright or Romanovsky-Giemsa stain, cerebrospinal fluid examination. Laboratory animal infections, RSK, RIF, ELISA |
| American trypanosoma (Trypanosoma cruzi)/ Blood | Swelling of the skin at the site of penetration, swelling of nearby lymph nodes, swelling of the eyelids, swelling of the parotid lymph nodes. The acute form in infants causes heart and brain damage leading to death. Chronic form in adults with childhood illness - arrhythmia, extrasystole, colon dilatation with wall hypertrophy, esophageal hypertrophy, myxedema, paralysis | Microscopy of blood smears, biopsy samples of lymph nodes, spleen and other organs - for the acute form. Serological studies, diagnosis of xenodiagnosis (eating uninfected bugs from the patient's body and detection of trypanosomes in their feces), infection of laboratory animals - for the chronic stage |
| Cutaneous leishmaniasis (Leishmania tropica)/Skin | Swollen lymph nodes on the skin, enlarged regional lymph nodes, ulcerated lymph nodes forming painless "dry" or "wet" ulcers, female lesions, scars on the skin after healing | Microscopy of tissue from the ulcer base stained with Romanovsky-Giemsa, RIF, RSK, ELISA |
| Cutaneous and mucous membrane leishmaniasis (Leishmania Braziliensis) / Skin and mucous membranes | Skin nodules, enlarged lymph nodes, skin ulcers, scar formation. On mucous membranes - painless disfiguring lesions of the mouth and nose, ulcers on the tongue, mucous membranes of the cheeks and nose, destruction of the nasal septum, hard palate, throat, fever, weight loss, bacterial infections | Microscopy of secretions from ulcers, biopsy of damaged organs, RSK, RNGA |
| Visceral leishmaniasis (Leishmania donovani)/ Spleen, liver, bone marrow, lymph nodes | Enlarged liver, enlarged spleen, anemia, exhaustion, poisoning, bleeding in the intestines, diarrhea, gray face and head, death | Detected in smears from spleen, lymph node, bone marrow biopsies, RIA, ELISA, RSK |
sporophyte
Sporozoans do not have locomotor organs. They consume nutrients throughout the body and often exhibit intracellular parasitism. Sporozoans include the agents that cause malaria and toxoplasma. Toxoplasmosis is more dangerous for pregnant women and people with proven immunodeficiency (for example, due to HIV infection).
Pregnant women with toxoplamosis are prescribed 3 million units of spiromycin three times a day, every day for fourteen to twenty days.
Parasites
Ciliates do not change body shape and have one seed. Motor operations are carried out due to the huge number of cilia that cover the entire cell.
Cilia have two nuclei: a large nucleus responsible for cell metabolism and a small nucleus that transmits genetic information.
Ciliates have an organized digestive system: the mouth of the cell is the mouth of the cell, the pharynx is the pharynx of the cell. Digestive enzymes are gradually released from the vacuole, ensuring complete digestion of nutrients. Undigested food parts will escape through the dough, forming especially at the end of the body. Symptoms that may occur when these parasites are present in the intestines are shown in the table below.
| pathogens | Localization | Symptom | Diagnose |
|---|---|---|---|
| Balantidium coli | Colon | Fever, poisoning, abdominal pain, diarrhea with mucus and blood, nausea, vomiting. Cyst carriers have no symptoms | Detected in stool and colon biopsy |
Treatment of balantidemia includes the prescription of antibacterial and antiprotozoal drugs according to one of the following regimens.
General characteristics of helminths
Helminths is the science of parasitic worms (helminths) on the bodies of other animals, the diseases they cause as well as methods of diagnosis, prevention and treatment.
The helminth fauna is the totality of all helminth species identified in humans. Helminths, unlike diseases caused by protozoa, are not common everywhere.
Most worms operate in the human gastrointestinal tract, while others can attack parenchymal organs, blood, and the genitourinary system.
The spread of helminths depends on people's labor activities, dietary habits of different population groups and the economic status of the country. The following types of helminths are the most common in our country.
Helminths are divided into geological helminths and biological helminths. To develop eggs or larvae of helminths, they need to be in the external environment to mature and acquire pathogenic properties. These are roundworms, whipworms, roundworms and others.
Biological helminths spend their life cycle with an alternative host and to acquire pathogenic properties, their eggs need to get inside an intermediate and sometimes an additional host. These are beef tapeworm, pork tapeworm, opisthorchis, fasciola and others.
The localization of parasitic worms or their larval forms in the human body is diverse: in the small and large intestines (intestinal helminthiasis), biliary tract and liver, blood, central nervous system and eyes, skin, muscle, etc. v. Intestinal parasites occur in humans more often than in lychees.
In the pathogenesis of helminths, the occurrence of allergic reactions and severe degenerative processes is of significant importance. They appear due to the large number of antigens that the worms have.
Other pathogenic factors include the direct influence of enzymes that form larval and adult forms. In the later stages of worm development, mechanical factors and direct traumatic effects of fixed organs play an important role.
Diagnosis is usually confirmed by interview, clinical picture of the disease, and detection of eggs, larvae, fragments, or adult worms in stool, sputum, and duodenal fluid.
Serological reactions, X-rays and ultrasound also play an important role in the diagnosis of helminthiasis.
In general, about three hundred species of pathogenic worms have been found in humans, of which 28 are the most common: 12 species of roundworms, 8 species of cestodes, 8 species of nematodes.