Parasitic infection

Medical quality assurance by Dr. Albrecht Nonnenmacher, MD at August 28, 2016
StartDiseasesParasitic infection

Parasitic infections occur when a microorganism invades another organism. Once the infection has occurred, the parasite then feeds off the host for survival. Some parasites live on the individual without causing symptoms, while others grow and produce toxins that make the person sick.


Definition & Facts

A parasitic infection is a disease caused or transmitted by a parasite. This type of infection can affect any living organism, including plants and humans. A parasitic infection is most common in rural, subtropical areas of the world where heat and humidity provide an ideal climate for parasites to thrive. Parasitic infections also occur in developed nations such as the United States.

There are three main types of parasites that cause infections. These are protozoans that cause protozoan infections, ectoparasites like fleas and ticks that cause ectoparasitic infections, and helminths (parasitic worms).

Malaria is the deadliest parasitic infection known to humans. It causes almost a million deaths per year – primarily among children in sub-Saharan Africa. Toxoplasmosis, trichomoniasis, and cryptosporidiosis are common parasitic infections to occur in the developed world. Most parasitic infections are treatable when they are caught early.

Symptoms & Complaints

The symptoms a person experiences depend upon the type of parasite causing their infection. Since many parasites are ingested, gastrointestinal symptoms are the most common complaint. For example, cryptosporidiosis can cause diarrhea, nausea, stomach cramps, and vomiting that lead to dehydration.

Pinworm infections (also known as enterobiasis) can cause anal itching, and schistosomiasis which is an infection with schistosoma (also known as blood flukes) can affect a person’s ability to breathe properly. Other symptoms of parasitic infections include the following:

Trichomoniasis, a sexually transmitted infection typically causes vaginal discharge or penile discharge and vaginal itching or penile itching.

Pinworms, tapeworms, and blood flukes are several parasites that do not always cause noticeable symptoms until they have reproduced and grown to a size that begins to interfere with the ability of the person’s body to function properly.

A person’s age, size and current health status can also affect the severity of the symptoms they experience. It is not uncommon for a person to be unaware of a parasitic infection until it has severely impacted their health.


There are many ways for parasitic infections to spread or be transmitted. The mode of transmission of an infection will depend upon which organism a person has been infected by. For instance, the parasite that mosquitoes carry causes malaria, which makes insect bites a common way for people to develop malaria.

Those who swim in lakes, rivers and ponds can accidentally ingest water that contains a parasite. Living in a place that lacks adequate sanitation systems can also make it more likely for a person to come into contact with parasites via unclean water and direct exposure to other people's bodily fluids.

People who work in careers that handle bodily fluids, such as daycare workers and nurses, are also at greater risk of contracting a parasite if they do not take proper precautions relating to hygiene.

Eating improperly cooked meat is another cause of these types of infections. Raw or undercooked meat is associated with parasitic worms that cause severe problems with the digestive system. Two types of parasitic infections associated with raw or undercooked meat are taeniasis and trichinosis.

Diagnosis & Tests

A parasitic infection can take time to diagnose since many of the symptoms mimic other conditions. After listening to a patient’s complaints and observing their physical symptoms, a physician may order a battery of tests. Blood tests, fecal exams, and colonoscopies are often utilized to make a diagnosis.

During a fecal exam, a stool sample is collected so that it can be analyzed for the presence of eggs. It is sometimes necessary to repeat this test since false negatives are common, especially in the early stages of an illness. A colonoscopy or endoscopy involves using a special tube with a camera attached at the end to peer into a person’s digestive tract. Visually observing a parasite is the surest way to verify an infection.

Parasites existing outside of the digestive system or excretory system are harder to detect through simple testing. Blood tests do not always provide conclusive results for patients who are infected with rare parasites.

For these patients, medical imaging tests my be required. Magnetic resonance imaging (MRI)s, X-rays, and computed tomography (CT) scans may be required to take a closer look at the organs of a person’s body. Using these tests, lesions and other abnormalities may be detected that can indicate a parasitic infection.

Treatment & Therapy

The treatments and therapies prescribed for a parasitic infection depend upon the specific parasite involved. For this reason, accurate testing is critical for providing a diagnosis that points toward the most effective treatment.

In some cases, no treatment is necessary since the person’s body will likely clear the infection on its own. For example, toxoplasmosis is a common parasite with which most people come into contact as a small child and whose symptoms usually go away on their own. Unless a person is pregnant or has a weakened immune system, this parasite will not cause harm as the body fights it off.

Many types of infections will require antibiotic, antiprotozoal, or anthelmintic treatment to kill off the parasite. Treatments may also be prescribed to treat specific symptoms such as diarrhea. This helps prevents further health complications from occurring while a person waits for their body to clear the infection.

Prevention & Prophylaxis

In most parts of the world, many parasitic infections are highly preventable. It is important to drink clean, bottled water when traveling to parts of the world that lack sanitary water sources.

Practicing proper hygiene is also the best way to avoid catching a parasite. Frequent hand washing, avoiding contact with fecal matter and practicing safe sex can prevent many common types of parasitic infections.

Efforts to prevent malaria include preventing insect bites by using insecticides as well as mosquito nets. Certain drugs like doxycycline may be taken prophylactically to prevent malaria as well.