Three Common Parasitic Opportunistic Infections

Symptoms and Prevention of Opportunistic Infections Caused by Parasites

Abstract microbes
Abstract microbes. Getty Images/Konstantin Inozemtsev/E+

Opportunistic infections, or OIs, are more common and usually more severe in people with weak immune systems, like in people infected with HIV. A parasitic opportunistic infection is one type of OI  — and it's considered one of the most frequent causes of death and illness in HIV-infected individuals, according to a 2011 article in Indian Journal of Medical Research

The good news is that opportunistic infections, including parasitic opportunistic infections, are now less common in people with HIV because of ART therapy.


That being said, gaining knowledge of the most common opportunistic infections will help people prevent them and take an active role in their immune system health.

What are the Most Common Parasitic Opportunistic Infections?

Of the parasitic opportunistic infections, the three most common are

  • toxoplasmosis
  • cryptosporidiosis
  • cystoisosporiasis. 

Let's take a closer look at these parasites, how they make a person feel, and how they can be prevented. 

Toxoplasmosis: Parasite of the Brain

Toxoplasmosis is caused by the parasite Toxoplasma gondii, which is carried by certain animals, like cats, rodents, and birds. These animals excrete the parasite in their feces, contaminating the soil. Infection can occur when someone breathes in contaminated dust or eats food contaminated with the parasite. Toxoplasmosis is also found in certain meats, especially red meat, and pork — so consuming undercooked meat products may also lead to infection.

According to the CDC, more than 60 million Americans carry the Toxoplasma parasite. But people with healthy immune systems usually have no symptoms or mild “flu-like” symptoms when infected. This is because their immune systems keep the parasite inactive or at bay in the body, preventing it from causing illness.

But in a person with a weakened immune system, such as a person infected with HIV — especially if their CD4 counts are less than 100 — a reactivated Toxoplasma infection usually affects the brain causing symptoms like:

  • Headache
  • Confusion
  • Muscle weakness
  • Poor coordination
  • Nausea
  • Fever
  • Seizures

Can Toxoplasmosis Be Prevented?

Yes, in addition to ART therapy, if a person has HIV and has CD4 counts less than 100, their healthcare provider will recommend a medication to prevent toxoplasmosis infection, usually trimethoprim-sulfamethoxazole (TMP-SMX). There are also behavioral strategies to prevent Toxoplasma infection. Some of these include:

  • Cat Care: Have someone else who is HIV negative and not pregnant change the litter box. If this is not possible, wear disposable gloves, change litter box daily, and avoid feeding cats raw or undercooked meats. Keep cats indoors. Avoid stray cats. A person with HIV with a cat does not need to have their cats tested or leave their cats. 
  • Hand Hygiene: Wash hands thoroughly with soap and warm water after gardening, changing cat litter, or any contact with soil or sand.
  • Safe Cooking/Consumption: Avoid raw or uncooked shellfish and meats, including lamb, pork, beef, and venison. Cook all meats to appropriate temperatures of 165 to 170°F. Freeze meats for several days at a sub-zero temperature to reduce the chance of infection. Peel and wash all fruits and vegetables before consuming. Clean all cooking equipment or surfaces thoroughly if in contact with raw or unwashed foods.

    Cryptosporidiosis & Cystoisosporiasis: Parasites in the Intestines

    Cryptosporidiosis is most commonly caused by the parasite Cryptosporidium hominis, Cryptosporidium parvum, or Cryptosporidium meleagridis. This parasite is spread in many ways, most commonly through contaminated water and food. Symptoms include abdominal pain and severe, watery diarrhea. Fever, nausea, and vomiting may also be present. 

    Cystoisosporiasis is caused by the parasite Cystoisospora belli, previously known as Isospora belli. Like Cryptosporidium, it affects the intestines, causes watery diarrhea, and is usually spread through contaminated food and water sources.

     According to the CDC, it's more common in tropical and subtropical climates. Other symptoms may include:

    • fever
    • headache
    • abdominal pain
    • vomiting
    • weight loss.

    Both cryptosporidiosis and cystoisosporiasis occur more commonly in people with HIV whose CD4 counts are less than 100, like toxoplasmosis infection. 

    Can Intestinal Parasites be Prevented?

    Yes, in addition to ART therapy, there are a number of strategies to prevent parasite-induced diarrhea in people with HIV who have low CD4 counts. Some of these include:

    • Hand Hygiene: Washing hands thoroughly after contact with human feces — like after changing a diaper on a baby— touching animals or pets, gardening, preparing and consuming food, and before and after sex.
    • Safe Sex: Using protection during sex to avoid direct or indirect contact with feces.
    • Water Safety: Avoid drinking water directly from lakes. Avoid swimming in or swallowing water from potentially contaminated bodies of water, including swimming pools. Consider drinking only filtered water. Avoid tap water, including ice, in developing countries.
    • Food Safety: Avoid eating raw oysters — specifically to prevent cryptosporidiosis


    AIDSinfo. (2015). Guidelines for the Prevention and Treatment of Opportunistic Infections in HIV-Infected Adults ad Adolescents. Retrieved September 18th, 2015.

    Centers for Disease Control and Prevention. (2015). Opportunistic Infections. Retrieved Septemeber 18th 2015.

    Nissapatorn V & Sawangjaroen N. Parasitic infections in HIV-infected individuals: Diagnostic and therapeutic challenges. Indian J Med Res. 2011 Dec;134(6):878-97. Retrieved September 18th, 2015. 

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