Parasites in the body

Human parasites are organisms that live on or inside the human body, obtaining nourishment and shelter at the expense of the host. These organisms can range from microscopic protozoa and helminths (worms) to larger arthropods. Parasites have different life cycles and modes of transmission and can affect different organs and systems of the body.

Unicellular parasites (protozoa) and multicellular parasites (helminths, arthropods) are complex from an antigenic and biochemical point of view, as is their life history and the pathogenesis of the diseases they cause. During their life, parasitic organisms usually go through several stages of development, accompanied by changes not only in structure, but also in biochemical and antigenic composition. Some larval stages of helminths bear little resemblance to the adult stages (e. g. tapeworms and trematodes). Some protozoan parasites also change significantly throughout their lives; for example Toxoplasma gondii is an intestinal coccidia in cats, but in humans it takes a different form and is localized in the deep tissues.

Some of these infections can progress from a well-tolerated or asymptomatic state to a life-threatening disease. Many parasitic infections are transmitted from animals to humans (zoonotic infections).

Protozoan parasites

Protozoa are single-celled microscopic organisms that can be free-living or parasitic in nature. Transmission of protozoa living in the human intestine to another person usually occurs via the fecal-oral route (for example, through contaminated food or water or through person-to-person contact). Protozoa living in human blood or tissues are transmitted to other people by arthropod vectors (for example, through the bite of a mosquito or fly).

Human protozoan parasites can be divided into four groups depending on their mode of movement.

1. Sarcodidae: use pseudopods for movement. It includes the amoebae Entamoeba (dysenteric liver abscess), Dientamoeba (colitis), and Acanthamoeba (can cause a serious, often fatal, infection of the brain and spinal cord called granulomatous encephalitis).
2. Flagellates (sarcomastigophores): Use flagella for movement. These include giardia (diarrhea), trypanosome (sleeping sickness and Chagas disease), leishmania (visceral, cutaneous, and mucocutaneous leishmaniasis), and trichomoniasis, a sexually transmitted infection (STI).
3. Apicocomplexes: The apical complex is used for movement. Includes Plasmodium (malaria), Toxoplasma (a zoonotic infection caused by the parasite Toxoplasma gondii with a wide range of clinical syndromes in humans).
4. Ciliates: Move via cilia and include Balanidium, a large protozoan, the only ciliate known to infect humans (dysentery). Approximately 1% of the world's population is infected with balantidiasis.

Helminths

Helminths are large multicellular organisms that, in the adult stage, are generally visible to the naked eye. Helminths can be free-living or parasitic in nature. In their adult form, helminths cannot reproduce in the human body. There are three main groups of human parasitic helminths:

• Trematodes: Fasciola Hepatica – liver fluke; Fasciolopsis buski – intestinal fluke; Paragonimus_westermani – lung fluke; Schistosome is a blood fluke.
• Tapeworms (tapeworms): Diphyllobothrium Latum – large tapeworm; Hymenolepis Nana - dwarf tapeworm; Taenia Saginata – bovine tapeworm; Taenia Solium: pork tapeworm.
• Roundworms (roundworms) cause various diseases in humans, which can be intestinal or directly affect some tissues. Ascaris
• Lubricoides – giant nematode; Enterobius Vermcularis - pinworms and others.

Ectoparasites

These are organisms that live externally on the skin of their hosts. Skin parasites feed on blood and epidermis. They are usually so small that they cannot be seen. Some species burrow into the skin, others live on the surface. Some parasites can spend their entire life cycle inside the human body, but many live outside the body, feeding only occasionally.

• Cimex Lectularius is a common parasite known as a bed bug.
• Dermatobia hominis is the larva of the human horsefly.
• Sarcoptes scabiei is a mite that causes scabies.

Human parasites affect millions of people around the world, especially in regions with limited access to clean water, sanitation and health care.

Causes of pathology

• Contaminated food and water. Inadequately treated or contaminated water sources can contain parasites such as Giardia Lamblia and Cryptosporidium, which lead to gastrointestinal infections. Eating undercooked or contaminated foods, especially raw or undercooked meat and seafood, can lead to the transmission of parasites such as Toxoplasma gondii and Trichinella spiralis.
• Poor hygiene and sanitation. Many parasitic infections, especially those caused by helminths (eg, roundworms and hookworms), are transmitted through contact with soil, food, or water contaminated with feces.
• Vector transmission through insect vectors. Parasites such as Plasmodium (malaria), Trypanosoma (Chagas disease, African sleeping sickness) and filariae (which cause lymphatic filariasis) are transmitted through the bites of infected insects: mosquitoes, bedbugs and midges.
• Animal-to-human transmission: Some parasites are reservoirs in animals, and humans can become infected through direct contact with infected animals or their excrement. For example, Toxoplasma gondii can be transmitted through contact with cat feces.
• Imported infections. Individuals traveling to regions where certain parasites are endemic may be at risk of contracting infections typically not found in their countries.
• Person-to-person transmission. Some body parasites, especially intestinal ones such as Enterobius vermcularis (pinworms) and Giardia Lamblia, can be transmitted through direct person-to-person contact, often in crowded or communal living conditions.
• Contaminated soil: Some types of helminths, including roundworms, can infect humans through contact with contaminated soil containing parasite eggs or larvae.

Symptoms of the disease

Helminthiasis can manifest itself with a variety of symptoms depending on the type of parasite in the human body, the site of the infection and the severity of the invasion:

• Abdominal pain, cramps and discomfort.
• Nausea and vomit.
• Diarrhea or constipation.
• Weight loss and malnutrition.
• Anemia due to loss of blood and nutrients.
• Worms visible in stool.
• Perianal itching (pinworm infection (Enterobius vermcularis) can cause perianal itching in children, especially at night).
• Respiratory symptoms: Some worms, such as Ascaris lumbricoides, can migrate into the respiratory tract, causing symptoms such as coughing and wheezing.
• High temperature: In some cases, helminth infections can cause low-grade fever.
• Infection with certain liver flukes or tapeworms can cause an enlargement of the liver (hepatomegaly) or spleen (splenomegaly).

Protozoa (protozoan parasites) very often cause diarrhea. Excessive diarrhea can lead to dehydration, a condition especially common in children under 5 years of age. Toxins released by the pathogen and entering the bloodstream cause weakness, pain in the abdomen and muscles. When the infection becomes chronic, weight loss and skin rashes appear.

Diagnosis of the disease

Diagnosis of parasitic infections involves a combination of clinical evaluation, laboratory testing for parasites, and sometimes imaging studies.

A detailed medical history, including information about travel to other countries, exposure to contaminated water or food, and symptoms, helps health care providers narrow down potential parasitic infections. A physical exam may reveal signs and symptoms associated with infections, such as skin rashes, abdominal tenderness, or enlarged organs.

Microscopic examination of stool samples is a common method for identifying intestinal parasites, including helminths (worms) and protozoa. If enterobiasis is suspected, a smear from the perianal area is prescribed, which is then examined under a microscope. Blood tests for parasites can be used to detect antibodies, antigens, or DNA from parasites.

• To diagnose echinococcosis, serological tests and sometimes ultrasound of the liver are prescribed.
• Opisthorchiasis is diagnosed by stool examination, serological tests, and sometimes DNA tests.
• Toxocariasis can be detected by tests to detect antibodies to Toxocara, a DNA test for parasites, and a general blood test showing eosinophilia.
• Giardiasis is diagnosed by stool analysis and serological tests.
• Stool microscopy and tests for roundworm antibodies are used to diagnose ascariasis.
• Trichinosis: serological tests and analysis of Trichinella DNA.

Urine samples can be tested for the presence of parasite eggs, larvae, or antigens, especially in infections such as schistosomiasis.

Radiological imaging, such as ultrasound, computed tomography, or magnetic resonance imaging, can be used to visualize and evaluate the extent of tissue damage caused by certain parasites, especially in cases of cystic or tissue-infiltrating parasites.

Treatment

Treatment of parasitic infections usually involves the use of antiparasitic drugs. The specific medications and length of treatment depend on the type of infection causing the infection, its severity, and the organs affected. Metronidazole and tinidazole are effective against a variety of protozoa, including Entamoeba histolytica and Giardialamlia. Atovaquone-proguanil: Used to treat and prevent malaria and some protozoan infections. Anthelmintic drugs include albendazole, praziquantel, ivermectin, pyrantel pamoate, sulfadiazine, suramin.

Disease prediction and prevention

The prognosis for treating parasites in the body varies widely depending on several factors, including the type of parasite, the severity of the infection, the organs affected, and the person's overall health. In many cases, timely and adequate treatment can lead to a favorable outcome, while lack of treatment or serious infections can lead to complications and long-term health consequences.

The human immune system plays an important role in determining the outcome of parasitic infection. Immunocompetent people may have a better prognosis than people with weakened immune systems.

The development of complications such as organ damage, chronic inflammation, or secondary infections can significantly affect the prognosis. Complications can result from long-term or untreated infections.

Some parasitic infections can become chronic and persist for a long period. Chronic infections can lead to ongoing health problems and can be difficult to manage.

Involvement of critical organs, such as the nervous, cardiovascular, or respiratory systems, can have a significant impact on prognosis. Parasites that attack vital organs can cause more serious and life-threatening complications.

Prevention of parasitic infections involves taking various measures to reduce the risk of infection and transmission. General recommendations to prevent parasite infestation are:

• Wash your hands thoroughly with soap and water after using the bathroom, before eating, and after touching pets or soil.
• Keep your nails short and clean to minimize the risk of getting parasite eggs or cysts under your nails.
• Cook meat, fish and poultry thoroughly to kill parasites. Wash fruit and vegetables carefully, especially if they will be eaten raw.
• Drink safe drinking water from purified or boiled sources, especially when traveling to areas with a high risk of waterborne parasites.
• Use insect repellent to prevent bites from mosquitoes, ticks and other vectors that can transmit parasitic diseases.
• Make sure your pets receive regular veterinary checkups and deworming medications.
• Dispose of pet waste correctly to minimize the risk of pest infestation.