Parasitic disease

A parasitic disease, also known as parasitosis, is an infectious illness caused by parasites. A parasite is an organism that derives its sustenance from a host. While the parasite gets the food it needs to survive, it causes harm to the host in the process. Scientists who study these organisms and the diseases they cause use the term parasitology.

Medical parasitology focuses on three major groups: parasitic protozoa, helminths, and parasitic arthropods. These pathogens belong taxonomically to either the animal kingdom or the protozoan kingdom.

There are different ways these organisms live and feed. Protozoa are single-celled, microscopic organisms belonging to the kingdom Protista. They obtain nutrients through processes called pinocytosis and phagocytosis. Helminths are macroscopic, multicellular organisms belonging to the kingdom Animalia. Within this group, helminths in the classes Cestoidea and Trematoda absorb their nutrients. Other helminths, known as nematodes, obtain nourishment through ingestion.

Parasites are categorized by where they live on a host. Most protozoa and helminths are endoparasites, meaning they live inside the body. Other parasites, called ectoparasites, live on the surface of the host.

Diseases can also be classified by how they progress. An acute form of a disease has a quick and often severe onset of symptoms. A chronic form is typically less severe but can last a lifetime. For example, Trypanosoma brucei rhodesiense causes acute illness, while Trypanosoma brucei gambiense causes chronic illness.

Infection can happen through several different pathways. Mammals may acquire parasites from contaminated food or water. Other methods include bug bites, sexual contact, or contact with animals. Specific behaviors like walking barefoot or having poor hygiene can increase risk. Eating undercooked foods or unwashed fruits and vegetables can also lead to infection. It is important to note that a parasite is only infectious during specific stages of its life cycle. Contact with non-infective stages will not result in an infection.

Many parasites utilize vectors to move between hosts. A vector acts as a vessel that helps the parasite infect its next host. Examples of parasitic diseases that rely on vectors include malaria, Lyme disease, and leishmaniasis.

These diseases are often concentrated in specific global regions. Most are prevalent along the equator because of the warm temperatures. People living in these tropical areas are at a much higher risk of contracting these diseases.

Risk factors often depend on social and environmental conditions. Parasitic diseases are far more common among marginalized groups. A lack of indoor bathrooms and limited access to clean drinking water are significant risk factors. In the United States, being Hispanic or African-American has been shown to be a risk factor for specific parasitic diseases.

Symptoms can be difficult to diagnose because they often resemble other ailments. A person might feel malaise, fever, or muscle pain, which looks like the flu or food poisoning.

Symptoms change depending on which organ the parasite targets. If the gastrointestinal tract is affected, a person may experience dysentery, constipation, or vomiting. If the lungs are the target, they might have a cough or blood in their sputum. Skin infections can cause local inflammation, rashes, or itching.

Doctors use various diagnostic methods to identify the specific parasite. These include stool tests, blood tests, or imaging like X-rays, CT scans, and MRIs. Some doctors may use a colonoscopy or endoscopy to see inside the body. Most infections are treated with antiparasitic drugs, though scientists have proposed using viruses to treat protozoa.