Parasites in the body

Human parasites are organisms that live in or on 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 body systems.

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. 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 have little in common with the adult stage (for example, tapeworms and worms). Some protozoan parasites also change a lot during their life; 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 a 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. Transmission of protozoa living in the human gut to other people usually occurs via the fecal-oral route (for example, through contaminated food or water or person-to-person contact). Protozoa that live in the blood or tissues of humans are transmitted to others through arthropod vectors (for example, through the bite of mosquitoes or midges).

Human protozoan parasites can be divided into four groups depending on the way they move.

1. Sarcodidae: Use pseudopodia for locomotion. Including the amoeba 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), 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. Including Plasmodium (malaria), Toxoplasma (a zoonotic infection caused by the parasite Toxoplasma gondii with various clinical syndromes in humans).
4. Ciliates: These move with 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 stage, can usually be seen with the naked eye. Helminths can be either free-living or parasitic. 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 – liverworm; Fasciolopsis buski - intestinal disorder; Paragonimus_westermani – pulmonary fluke; Schistosoma is a blood disease.
• Cestodes (tapeworms): Diphyllobothrium Latum – broad tapeworm; Hymenolepis Nana – dwarf tapeworm; Taenia Saginata – cattle 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 host. 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 most 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 fly.
• Sarcoptes scabiei is the mite that causes scabies.

Human parasites affect millions of people worldwide, especially in areas with limited access to clean water, sanitation and health care.

Pathological causes

• Contaminated food and water. Untreated or contaminated water sources may contain parasites such as Giardia Lamblia and Cryptosporidium, which lead 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 soil, food or water contaminated with feces.
• Vector transmission via insect vectors. Parasites such as Plasmodium (malaria), Trypanosoma (Chagas disease, African sleeping sickness) and filarial worms (causing lymphatic filariasis) are spread 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 feces. For example, Toxoplasma gondii can be transmitted through contact with cat feces.
• Imported infection. Individuals traveling to areas where certain parasites are endemic may be at risk of contracting an infection not normally found in their home country.
• Person to person delivery. Some parasites in the body, especially intestinal ones such as Enterobius vermcularis (pinworms) and Giardia Lamblia, can be spread 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.

Disease symptoms

Helminthiasis can manifest itself in various 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.
• Dizziness and vomiting.
• Diarrhea or constipation.
• Weight loss and malnutrition.
• Anemia due to loss of blood and nutrients.
• Visible worms in stool.
• Infection of perianal itching (pinworm (Enterobius vermcularis) can cause perianal itching in children, especially at night).
• Respiratory symptoms: Some worms, such as Ascaris lumbricoides, can migrate to 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 liverworms 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 common condition in children under the age of 5. Toxins released by pathogens and entering the bloodstream cause weakness, pain in the stomach and muscles. When the infection becomes chronic, weight loss and skin rashes appear.

Disease diagnosis

Diagnosis of parasitic infection 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 the possibility of parasitic infection. A physical examination may reveal signs and symptoms associated with infection, 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 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 liver ultrasound are prescribed.
• Opisthorchiasis is diagnosed using stool examination and serological tests, and sometimes DNA testing.
• Toxocariasis can be detected through a test to detect antibodies to Toxocara, a DNA test for the parasite, and a general blood test that shows eosinophilia.
• Giardiasis is diagnosed using stool analysis and serological tests.
• To diagnose ascariasis, stool microscopy and tests for antibodies against ascaris are used.
• Trichinosis: serological testing 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 parasites or tissue infiltration.

Treatment

Treatment for 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 prediction and prevention

The prognosis for treating parasites in the body varies depending on several factors, including the type of parasite, the severity of the infection, the organ system affected, and the person's overall health. In most cases, prompt and appropriate treatment can lead to favorable outcomes, 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 parasitic infections. People who are immunocompetent may have a better prognosis than people with weakened immune systems.

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

Some parasitic infections can be chronic and persist for a long period of time. 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 invade vital organs can cause more serious and life-threatening complications.

Prevention of parasitic infections involves taking various steps 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 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 sources that have been purified or boiled, especially when traveling to areas with a high risk of waterborne parasites.
• Use insect repellent to avoid mosquito bites, ticks and other vectors that can carry parasitic diseases.
• Make sure your pet receives regular veterinary checkups and deworming.
• Dispose of pet waste properly to minimize the risk of pest infestation.