A persistent infection is one in which a virus, bacterium or other pathogen is not eliminated by the host immune system and remains within the host for long periods. Rather than being cleared after acute disease, the agent continues replicating at low levels or lies dormant, leading to chronic or intermittent presence of the pathogen or its genetic material.
Mechanisms and Types
Persistent infections arise when pathogens evade immune responses or find niches with limited immune surveillance. Viruses may integrate into the host genome, establish latency in long‑lived cells, or downregulate antigen expression. Persistent infections can be classified into chronic infections, in which new virions or bacteria are continuously produced, and latent infections, where replication is silenced and reactivation occurs periodically. Slow infections involve a prolonged incubation followed by progressive disease, as seen with prion diseases.
During chronic infection the pathogen replicates and sheds for months or years, often causing ongoing inflammation. Hepatitis B virus and hepatitis C virus persist in hepatocytes and can lead to cirrhosis and hepatocellular carcinoma. Human immunodeficiency virus integrates into the genome of CD4‑positive T cells, establishing a lifelong infection despite antiviral therapy. Latent infections include herpes simplex viruses and varicella‑zoster virus, which remain in sensory ganglia and can reactivate as cold sores or shingles. Measles virus can persist in the brain and, years later, cause subacute sclerosing panencephalitis.
Examples and Public Health Importance
Persistent bacterial infections such as Mycobacterium tuberculosis can remain dormant in lung tissue, leading to reactivation disease years after primary exposure. Persistent human papillomavirus infection of the cervix is a major risk factor for cervical cancer. In veterinary medicine, lentiviruses and retroviruses cause lifelong infection in their hosts. Plant viruses also establish persistent infections in perennial crops. Understanding persistence helps in designing vaccines and treatments that target reservoirs and prevent reactivation.
Persistent infections challenge the immune system and can result in chronic disease, transmission, or late complications. Recognizing the mechanisms by which pathogens persist aids in developing strategies to clear or control these long‑term infections.
Related Terms: Latent Infection, Chronic Infection, Carrier State, Immune Evasion, Viral Latency