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 can affect different organs and systems of the body.

Unicellular parasites (protozoa) and multicellular parasites (helminths, arthropods) are complex antigenically and biochemically, as well as 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 significantly during their lifetime; 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 condition to life-threatening disease. Many parasitic infections are transmitted from animals to humans (zoonosis).

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 via the fecal-oral route (eg, contaminated food or water or person-to-person contact). Protozoa that live 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. 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), trypanosomiasis (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 zoonosis 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 are usually visible to the naked eye in adulthood. 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 – lung fluke; Schistosoma is a blood fluke.
• Cestodes (tapeworms): Diphyllobothrium Latum – broad tapeworm; Hymenolepis Nana – dwarf tapeworm; Taenia Saginata – beef 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 a bed bug.
• Dermatobia hominis is the larva of the human roach.
• Sarcoptes scabiei is the mite that causes scabies.

Human parasites affect millions of people worldwide, 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 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 transmission of parasites such as Toxoplasma gondii and Trichinella spiralis.
• Poor hygiene and sanitary conditions. Many parasitic infections, especially those caused by helminths (eg, roundworms, hookworms), are transmitted by contact with faecal-contaminated soil, food, or water.
• Vector transmission via insect vectors. Parasites such as Plasmodium (malaria), Trypanosoma (Chagas disease, African sleeping sickness) and filarial worms (causing lymphatic filariasis) are transmitted by the bite of infected insects: mosquitoes, bed bugs 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 feces. 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 infection not normally found in their countries.
• Person-to-person transmission. Some body parasites, especially intestinal parasites such as Enterobius vermcularis (pinworms) and Giardia Lamblia, can be transmitted by direct person-to-person contact, often in crowded or community settings.
• 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 be manifested by different symptoms depending on the type of parasite in the human body, the location of the infection and the severity of the invasion:

• Abdominal pain, cramps and discomfort.
• Nausea and vomiting.
• Diarrhea or constipation.
• Weight loss and malnutrition.
• Anemia due to loss of blood and nutrients.
• Visible worms in the 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 fever: in some cases, helminthic infections can cause a low fever.
• Infection with some liver flukes or tapeworms can cause enlargement of the liver (hepatomegaly) or spleen (splenomegaly).

Protozoa (protozoan parasites) most often cause diarrhea. Excessive diarrhea can lead to dehydration, a condition that is especially common in children under the age of 5. 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.

Disease diagnosis

Diagnosis of parasitic infections involves a combination of clinical assessment, 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 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 enterobiosis 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 parasite DNA.

• To diagnose echinococcosis, serological tests are prescribed, and sometimes liver ultrasound.
• Opisthorchiasis is diagnosed by stool examination and serological tests, and sometimes DNA testing.
• Toxocariasis can be detected by tests for antibodies to Toxocara, a DNA test for parasites, and a general blood test that shows eosinophilia.
• Giardiasis is diagnosed by stool analysis and serological tests.
• Stool microscopy and ascaris antibody tests are used to diagnose ascariasis.
• 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.

Radiological 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 in cases of 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 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.

Disease prognosis and prevention

The prognosis for treating parasites in the body varies greatly depending on several factors, including the type of parasite, the severity of the infection, the organ systems involved, and the person's overall health. In many cases, prompt and proper treatment can lead to a favorable outcome, while lack of treatment or severe infection 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. Immunocompetent individuals may have a better prognosis than individuals with a weakened immune system.

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 last for a long time. Chronic infections can lead to ongoing health problems and are difficult to treat.

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 for preventing parasite infestation are:

• Wash your hands thoroughly with soap and water after using the toilet, before eating, and after touching pets or the ground.
• Keep your nails short and clean to reduce the risk of getting parasite eggs or cysts under your nails.
• Cook meat, fish and poultry thoroughly to kill parasites. Wash fruits and vegetables well, especially if you are going to eat them 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 have regular veterinary checkups and deworming medications.
• Dispose of pet waste properly to reduce the risk of pest infestation.