Chronic infections are long-term infections that persist for months or even years. They are caused by certain pathogens that can evade the immune response, and they can result in chronic inflammation and tissue damage. The pathogenesis of chronic infections involves a complex interplay between the pathogen and the host immune response. Here are some examples of the mechanisms involved in chronic viral, bacterial, and fungal infections:
- Chronic viral infections:
Viral infections can persist in the host for a long time, as the virus can evade the immune response and establish a latent infection. During latency, the virus is not actively replicating, but it can reactivate later, leading to recurrent infections. The following are examples of viral infections that can become chronic:
- Hepatitis B virus (HBV) and hepatitis C virus (HCV): These viruses can establish a chronic infection that can lead to chronic liver disease, cirrhosis, and liver cancer. The chronic infection is characterized by persistent inflammation, immune cell infiltration, and tissue damage.
- Human immunodeficiency virus (HIV): HIV infects immune cells, particularly CD4+ T cells, and can cause acquired immunodeficiency syndrome (AIDS) if left untreated. HIV can persist in the body for years, even with antiretroviral therapy, due to the formation of viral reservoirs.
- Chronic bacterial infections:
Bacterial infections can also become chronic due to the ability of bacteria to evade the immune response and form biofilms, which are communities of bacteria encased in a protective matrix. Chronic bacterial infections are associated with persistent inflammation and tissue damage. The following are examples of bacterial infections that can become chronic:
- Tuberculosis: Mycobacterium tuberculosis can evade the immune response by residing in macrophages and forming granulomas, which are clusters of immune cells that surround the bacteria. The granulomas can become calcified and persist for years, leading to chronic infection and lung damage.
- Staphylococcus aureus: This bacterium can form biofilms on medical devices and in tissues, leading to chronic infections such as osteomyelitis (bone infection) and endocarditis (heart valve infection).
- Chronic fungal infections:
Fungal infections can also become chronic due to the ability of fungi to evade the immune response and form biofilms. Chronic fungal infections are associated with persistent inflammation and tissue damage. The following are examples of fungal infections that can become chronic:
- Aspergillosis: Aspergillus fumigatus can form biofilms in the lungs of immunocompromised patients, leading to chronic lung infections.
- Candidiasis: Candida albicans can form biofilms on medical devices and in tissues, leading to chronic infections such as catheter-associated urinary tract infections and oral thrush.
In chronic infections, the immune response can become dysregulated, leading to persistent inflammation and tissue damage. Therapeutic strategies for chronic infections aim to restore the balance between the pathogen and the immune response, either by enhancing the immune response or by reducing the pathogen load.