Parasites in the body

Human parasites are organisms that live on or inside the human body, obtaining nutrients 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 they can affect different organs and systems of the body.

Unicellular parasites (protozoa) and multicellular parasites (helminths, arthropods) are complex antigenically and biochemically, 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 (for example, tapeworms and flukes). Some protozoan parasites also change greatly during their lives; for example, Toxoplasma gondii is an intestinal coccidia in cats, but in humans it takes a different form and is localized in deep tissues.

Some of these infections can progress from a well-tolerated or asymptomatic state to life-threatening illness. 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 that live in the human intestine to another person usually occurs through the fecal-oral route (for example, through contaminated food or water or person-to-person contact). Protozoa that live in human blood or tissue are transmitted to other people by arthropod vectors (for example, through the bite of a mosquito or mosquito fly).

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

1. Sarcodidae: Use pseudopodia for movement. Includes the amoebas 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): uses 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 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: These move by cilia and include Balanidium, a large protozoan, the only ciliate known to infect humans (dysentery). About 1% of the world's population is infected with balantidiasis.

Helminths

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

• Trematodes: Fasciola Hepatica – liver fluke; Fasciolopsis buski – intestinal fluke; Paragonimus_westermani – pulmonary fluke; Schistosoma is a blood fluke.
• Cestodes (tapeworms): Diphyllobothrium Latum – wide tapeworm; Hymenolepis Nana – dwarf tapeworm; Taenia Saginata – bovine tapeworm; Taenia Solium - pork tapeworm.
• Nematodes (roundworms) cause various diseases in humans, which can be intestinal or directly affect certain tissues. Ascaris
• Lumbricoides – giant roundworm; 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 bed bug.
• Dermatobia hominis is the larva of the human gadfly.
• 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 healthcare.

Causes of pathology

• Contaminated food and water. Inadequately treated or contaminated water sources may contain parasites such as Giardia Lamblia and Cryptosporidium, leading to gastrointestinal infections. Eating undercooked or contaminated food, 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, hookworms), are transmitted through contact with fecally contaminated soil, food, or water.
• Vector transmission through insect vectors. Parasites such as Plasmodium (malaria), Trypanosoma (Chagas disease, African sleeping sickness) and filarial worms (causing 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 not typically found in their countries.
• Transmission from person to person. Some parasites in the body, 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 nematodes, can infect humans through contact with contaminated soil containing parasite eggs or larvae.

Symptoms of the disease

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

• Abdominal pain, cramping and discomfort.
• Nausea and vomiting.
• Diarrhea or constipation.
• Weight loss and malnutrition.
• Anemia due to loss of blood and nutrients.
• Visible worms in stool.
• Perianal itching (pinworm (Enterobius vermcularis) infection 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, helminthic infections can cause low-grade fever.
• Infection with some liver flukes or tapeworms can cause the liver (hepatomegaly) or spleen (splenomegaly) to become enlarged.

Protozoa (protozoan parasites) most often cause diarrhea. Excessive diarrhea can lead to dehydration, which is a condition that is 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 tests 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 examination may reveal signs and symptoms associated with infections, such as 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 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 using stool examination and serological tests, and sometimes DNA testing.
• 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 using stool analysis and serological tests.
• To diagnose ascariasis, stool microscopy and tests for antibodies to ascaris are used.
• Trichinosis: serological tests and DNA analysis of Trichinella.

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 MRI, 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 for parasitic infections usually involves the use of antiparasitic medications. The specific medications and duration 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 protozoal infections. Anthelmintic drugs include albendazole, praziquantel, ivermectin, pyrantel pamoate, sulfadiazine, suramin.

Forecast and prevention of the disease

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 overall health of the person. In many cases, prompt and proper treatment can lead to a favorable 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 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 arise 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 organ systems, such as the nervous, cardiovascular, or respiratory systems, may 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 for preventing parasite infestation are:

• Wash your hands thoroughly with soap and water after using the toilet, 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 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.
• Ensure your pets receive regular veterinary checkups and deworming medications.
• Properly dispose of pet waste to minimize the risk of pest infestation.