What Is a Latent Infection?

A latent infection is an infection by an organism that lies hidden or dormant (inactive) in the body. Whereas active infections are where an organism is actively replicating and potentially causing symptoms, latent infections are static and typically cause no symptoms. While an infection is latent, it may hide from the immune system and be difficult to treat with drugs and other therapies.

Learn about the different types of latent infections, including causes, treatment methods, and more.

Types of Latent Infections

Different types of organisms can intrude on the body and cause a latent infection. Although some types of latent infections are more common than others, the organisms involved in all types are usually inactive and cause no symptoms.

Viral Latent Infections

Viral latent infections are infections caused by viruses, which are organisms containing genetic material such as deoxyribonucleic acid (DNA). Common types of latent viral infections include:

Herpes Simplex Virus (HSV)

Commonly known as herpes, herpes simplex virus (HSV) can cause sores on or in the mouth or genitals. HSV is categorized into two types: HSV-1 and HSV-2. HSV-1 mainly affects the mouth and face, and HSV-2 generally affects the genital area.

After the initial infection, the herpes virus stays dormant in the body for a lifetime and can cause symptoms like cold sores or genital warts from time to time. However, the virus rarely causes serious health risks for those who are healthy and nonpregnant, and symptoms typically clear with or without treatment.

Varicella Zoster Virus (VZV)

Varicella-zoster virus (VZV) is the virus that causes the common childhood disease known as chickenpox (varicella). After a chickenpox infection, VZV can remain in the body for a lifetime and potentially reactivate and cause the blistering condition known as shingles in older adults.

Disease from VZV infection generally does not cause serious health problems and can be treated with medication and protected against with vaccination.

Human Immunodeficiency Virus (HIV)

Human immunodeficiency virus (HIV), the virus known to affect the immune system and develop into acquired immunodeficiency syndrome (AIDS), can infect immune system cells and become latent. HIV latency can occur even when a person infected with the virus is receiving standard HIV treatment known as antiretroviral therapy (ART).

ART does a good job of preventing active HIV viruses from replicating, which helps to prevent disease progression. However, the viruses that become dormant in immune cells go unnoticed by the immune system and do not respond to ART, and may reactivate in the future.

HIV latency is a major reason why HIV cannot entirely be cured. But research is ongoing to find ways for medications and the immune system to notice and terminate latent HIV-infected cells.

Bacterial Latent Infections

Bacteria or single-celled organisms can cause latent infections. An infection from the bacterium Mycobacterium tuberculosis is the most common type, which causes the condition known as tuberculosis (TB). Around two billion people are infected by this bacterium worldwide.

While TB bacterial infection can lead to sickness, the bacterium can live in the body and remain latent for a lifetime. If TB bacteria become active, it can lead to TB, which can be serious if not treated properly. However, the correct use of vaccines and medicines can help prevent or cure most TB cases.

Parasitic Latent Infections

Parasites are organisms that live in or on another organism to survive. The parasite known as Toxoplasma gondii is the most common parasite that infects the population.

When active in the body, T. gondii can cause the condition known as toxoplasmosis. But the parasite can become latent and live in the body for a lifetime. Toxoplasmosis disease can resolve without treatment in those who are healthy and nonpregnant but can be treated with medications if it causes illness or poses health risks.

A tapeworm infection is another type of parasitic infection that is sometimes considered latent. An infection can occur from swallowing the larvae of a tapeworm when contaminated food or fingers are put in the mouth.

These larvae can form cysts in body tissues that remain for multiple years, potentially causing a condition known as cysticercosis. With cysticercosis, the cysts formed from the larvae die and irritate the tissues around them, causing them to swell. While some people may not need treatment for cysticercosis, medications are available if the condition is too bothersome.

Latent Infection Symptoms

Typically, latent infections cause no noticeable symptoms. Symptoms usually develop when dormant organisms in the body become active and cause disease. Symptoms may vary from one disease to another, but common ones include:

• Fever
• Weakness
• Fatigue
• Chills
• Coughing
• Body Aches
  

Causes

Latent infections can be caused by coming in contact with an infected surface, person, food, or beverage. Parasitic latent infections from tapeworm and toxoplasmosis parasites usually develop after handling, eating, or drinking contaminated food or beverages.

Some infectious bacteria, like TB bacteria, can spread through the air by way of infectious droplets after an infected person coughs, sneezes, or laughs. Viral infections like HSV and VZV typically spread through physical contact with infected sores, saliva, or surfaces.

Diagnosis

Since latent infections are usually asymptomatic, laboratory testing is a standard measure used to form a diagnosis. Lab tests help identify the type of organism that's causing an infection, which paves the way for knowing what to do for treatment if necessary. Some of the most common lab tests for latent infections include:

• Urine tests (urinalysis)
• Blood tests
• Stool cultures

For some latent infections, imaging tests are needed to help form a precise diagnosis. For instance, to know if someone is infected by TB bacteria, a healthcare provider will commonly order a purified protein derivative (PPD) test (also known as the TB skin test).

If the test is positive, a chest x-ray may be ordered to see where abnormalities or lesions are present in the lungs before using other diagnostic measures.

Treatment

For those in good health, a latent infection may not need treatment. A healthy immune system is generally able to clear many types of infections or prevent an inactive organism from becoming active.

Treatment may be needed in those who are pregnant or have weakened immune systems. For example, research shows that those who are pregnant and have latent TB infection have elevated pregnancy and birth complication risks if they don't receive treatment.

And for those with weakened immune systems, a latent infection poses the risk of becoming an active infection and causing severe illness.

Treatment depends on the type of infection, especially when a latent infection becomes an active one. Treating TB with antibiotics like isoniazid (INH) and Priftin (rifapentine) is common, while an antiparasitic like Daraprim (pyrimethamine) is typically used for a parasitic disease like toxoplasmosis.

ART, which includes medicines like nucleoside reverse transcriptase inhibitors (NRTs), is used for HIV treatment, while antiviral medications like Zovirax (acyclovir) are used to treat HSV and VZV.

Summary

A latent infection is an infection by an organism that remains inactive in the body. A latent infection typically causes no symptoms, but the inactive organism may reactivate and cause sickness. Many latent infections don't require treatment unless there are risks of severe illness or other complications from an infection.

A Word From Verywell

It can be difficult to know if you have a latent infection, as such infections typically present no symptoms. However, if you learned that you were in close vicinity or in contact with someone with an infection that can become latent, such as TB, you should visit your healthcare provider to get screened.

Doing so can help determine if you have an infection and if treatment is needed, which is important if you are pregnant or have an autoimmune disorder like HIV.