Parasites in the body

Human parasites are organisms that live on or inside the human body and obtain food 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 antigenically and biochemically complex, as are their life histories and the pathogenesis of the diseases they cause. Parasitic organisms usually go through several stages of development during their life, 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 (for example, tapeworms and flukes). Some protozoan parasites also vary greatly throughout their lives; for example, Toxoplasma gondii is an intestinal coccidia in cats, but in humans it takes a different form and localizes in deeper tissues.

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

Protozoan parasites

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

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

1. Sarcodidae: Use pseudopodia for locomotion. Amoebas include Entamoeba (dysenteric liver abscess), Dientamoeba (colitis), and Acanthamoeba (which 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), trypanosoma (sleeping sickness and Chagas disease), leishmania (visceral, cutaneous and mucocutaneous leishmaniasis), and trichomoniasis, a sexually transmitted infection (STI).
3. Apicomplexes: The apical complex is used for locomotion. Includes Plasmodium (malaria), Toxoplasma (a zoonotic infection caused by the Toxoplasma gondii parasite, which is accompanied by a wide range of clinical syndromes in humans).
4. Cilia: These include Balanidium, a large protozoan with cilia that moves through cilia and is the only one known to infect humans (dysentery). About 1% of the world's population is infected with balantidiasis.

Helminths

Helminths are large multicellular organisms that are usually visible to the naked eye in their adult stages. Helminths can be both free-living and parasitic. In the adult form, helminths cannot multiply in the human body. There are three main groups of helminths that are parasites of humans:

• Trematodes: Fasciola Hepatica – liver flu; Fasciolopsis buski - intestinal tumor; Paragonimus_westermani – lung congestion; Schistosoma is a blood fluke.
• Cestodes (tapeworms): Diphyllobothrium Latum – broad tapeworm; Hymenolepis Nana – dwarf tapeworm; Taenia Saginata – bovine tapeworm; Taenia Solium - pork worm.
• Nematodes (roundworms) cause various diseases in humans, they can be in the intestine or directly affect certain tissues. Ascaris
• Lumbricoides - giant roundworm; Enterobius Vermcularis - pinworms and others.

Ectoparasites

These are organisms that live outside the skin of their owners. Skin parasites feed on blood and epidermis. They are usually so small that they are not visible. Some species penetrate 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 the bed bug.
• Dermatobia hominis is a human gadfly larva.
• Sarcoptes scabiei is a tick that causes scabies.

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

Causes of pathology

• Contaminated food and water. Inadequately treated or contaminated water sources may contain parasites such as Giardia Lamblia and Cryptosporidium, which cause gastrointestinal infections. Eating undercooked or contaminated food, especially raw or undercooked meat and seafood, can cause transmission of parasites such as Toxoplasma gondii and Trichinella spiralis.
• Poor hygiene and sanitation. Many parasitic infections, especially those caused by helminths (eg, roundworms, hookworms), are caused by 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 filarial worms (which cause lymphatic filariasis) are transmitted by the bites of infected insects: mosquitoes, bedbugs and midges.
• Animal-to-human transmission: Some parasites are reservoirs in animals, and humans can come into direct contact with infected animals or their feces. For example, Toxoplasma gondii can come into contact with cat feces.
• Imported infections. Individuals traveling to areas where certain parasites are endemic may be at risk of contracting infections not commonly found in their home countries.
• Human-to-human transmission. Some parasites in the body, especially intestinal ones such as Enterobius vermcularis (pinworms) and Giardia Lamblia, can be transmitted by direct person-to-person contact, often in crowded or communal living conditions.
• Contaminated soil: Some types of helminths, including nematodes, can infect humans through contact with contaminated soil containing parasitic eggs or larvae.

Symptoms of the disease

Helminthosis can manifest itself with different symptoms depending on the type of parasite in the human body, the place of infection and the severity of the infestation:

• Abdominal pain, cramping and discomfort.
• Nausea and vomiting.
• Diarrhea or constipation.
• Weight loss and nutrition.
• Anemia due to loss of blood and nutrients.
• Worms seen in feces.
• Perianal itching (pinworm (Enterobius vermcularis) infection can cause perianal itching in children, especially at night).
• Respiratory symptoms: Some worms, such as Ascaris lumbricoides, can enter the respiratory tract and cause symptoms such as coughing and wheezing.
• High temperature: in some cases, helminthic infections can cause low-grade fever.
• Infection with some liver flukes or tapeworms can cause an enlarged liver (hepatomegaly) or spleen (splenomegaly).

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

Diagnosis of the disease

The diagnosis of parasitic infections involves a combination of clinical evaluation, laboratory tests for parasites, and sometimes imaging studies.

A detailed medical history, including travel to other countries, exposure to contaminated water or food, and symptoms, helps health care providers rule out potential parasitic infections. A physical examination may reveal signs and symptoms associated with infections, such as a skin rash, abdominal tenderness, or enlarged organs.

Microscopic examination of stool samples is a common method for identifying intestinal parasites, including helminths (worms) and protozoa. If enterobiosis is suspected, a smear from the perianal region 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 examination of the liver are prescribed.
• Opisthorchosis is diagnosed by stool examination and serological tests, and sometimes DNA testing.
• Toxocariasis can be detected by tests to detect antibodies against Toxocara, a DNA test for parasites, and a complete blood test showing eosinophilia.
• Giardiasis is diagnosed using stool analysis and serological tests.
• For the diagnosis of ascariasis, stool microscopy and tests for antibodies against ascaris are used.
• Trichinosis: serological tests and Trichinella DNA analysis.

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

Radiologic imaging, such as ultrasound, computed tomography, or MRI, can be used to visualize and assess the extent of tissue damage caused by certain parasites, especially cystic or tissue-infiltrating parasites.

Treatment

Treatment of parasitic infections usually involves the use of antiparasitic drugs. Specific medications and duration of treatment depend on the type of infection causing the infection, its severity, and the affected organs. 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 protozoal infections. Anthelmintic drugs include albendazole, praziquantel, ivermectin, pyrantel pamoate, sulfadiazine, suramin.

Disease prognosis 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 organ systems affected, and the person's overall health. In many cases, prompt and proper treatment can lead to a positive outcome, while lack of treatment or severe infections can lead to complications and long-term health consequences.

The human immune system plays an important role in determining the outcome of a parasitic infection. People who are immunocompromised 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 last for a long time. Chronic infections can cause ongoing health problems and can be difficult to manage.

Involvement of critical organ systems 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 infection:

• Wash your hands thoroughly with soap and water after using the restroom, 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 fruits and vegetables thoroughly, especially if they are to 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 get regular veterinary checkups and worming.
• Dispose of pet waste properly to minimize the risk of pest infestation.