Parasites in the body

Human parasites are organisms that live on or inside the human body and obtain 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 (protozoa) and multicellular (helminths, arthropods) parasites are antigenically and biochemically complex, as are their biological 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 their structure, but also in their biochemical and antigenic composition. Some larval stages of helminths bear little resemblance to adult stages (e. g. , tapeworms and flukes). Some protozoan parasites also change considerably during their lifespan; 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 a life-threatening illness. 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 that live in the human gut to another person usually occurs by the fecal-oral route (for example, through contaminated food or water or person-to-person contact). Protozoa that live in human blood or tissues 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 based on their mode of movement.

1. Sarcodidae: use pseudopods for movement. 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): 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. Apicomplexa: 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:  They 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 the adult stage, are usually visible to the naked eye. Helminths can be free 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 – large 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. Roundworm
• Lumbricoides – giant roundworm; Enterobius Vermcularis - pinworms and others.

Ectoparasites

These are organisms that live outside the skin of their hosts. Skin parasites feed on blood and the epidermis. They are usually so small that you cannot see them. 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 and only feed occasionally.

• Cimex Lectularius is a common parasite known as a bedbug.
• 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 areas where access to clean water, sanitation and health care is limited.

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 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, particularly those caused by helminths (e. g. , roundworms, hookworms), are transmitted by contact with soil, food, or water contaminated with feces.
• Vector transmission by 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 andmidges.
• 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. People traveling to areas where certain parasites are endemic may be at risk of contracting infections not typically found in their country.
• Person-to-person transmission. Some parasites in the body, including intestinal parasites, such as Enterobius vermcularis (pinworms) and Giardia Lamblia, can be transmitted by direct person-to-person contact, often in crowded or community living conditions.
• Contaminated soil: Certain 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 with various symptoms depending on the type of parasite present in the human body, the place of 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.
• Worms visible in stools.
• 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, helminthic infections can cause a mild fever.
• Infection with certain liver flukes or tapeworms can cause an enlargement of the liver (hepatomegaly) or spleen (splenomegaly).

Protozoa (protozoan parasites) most often cause diarrhea. Excessive diarrhea can lead to dehydration, a condition particularly common in children under 5 years old. 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

Diagnosing parasitic infections involves a combination of clinical assessments, laboratory tests to detect parasites, and sometimes imaging studies.

A detailed medical history, including information on travel to other countries, exposure to contaminated water or food, and symptoms, helps health care providers identify potential parasitic infections. A physical exam may reveal signs and symptoms associated with infections, such as a 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 region is prescribed, which is then examined under a microscope. Blood tests to detect parasites can be used to detect antibodies, antigens, or parasite DNA.

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

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

Radiological imaging, such as ultrasound, CT or MRI, can be used to visualize and assess the extent of tissue damage caused by certain parasites, particularly in cases of cystic or tissue-infiltrating parasites.

Treatment

Treatment of 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 various protozoa, including Entamoeba histolytica and Giardialamlia. Atovaquone-proguanil: Used to treat and prevent malaria and certain protozoan infections. Anthelmintic drugs include albendazole, praziquantel, ivermectin, pyrantel pamoate, sulfadiazine, and 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 organ systems affected, and the person's overall health. In many cases, prompt and appropriate 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 a 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 occur from long-term or untreated infections.

Some parasitic infections can become chronic and persist for a long time. Chronic infections can cause ongoing health problems and 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 lead to more serious and even fatal complications.

Preventing parasitic infections involves taking various measures to reduce the risk of infection and transmission. General recommendations for preventing parasitic infestations include:

• Wash your hands thoroughly with soap and water after using the toilet, before eating, and after touching animals 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 carefully, especially if they will be eaten raw.
• Drink drinking water from purified or boiled sources, especially when traveling to areas at 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 exams and deworming medications.
• Dispose of pet waste properly to minimize the risk of pest infestation.