Definition
Latent refers to a state in which an organism, virus or trait is present but not currently active or expressing. In microbiology, latent phases are periods of dormancy without observable symptoms or replication.
Explanation
Latent states occur across different biological contexts. Viruses such as herpesviruses and varicella zoster establish latency within host cells, maintaining their genomes as episomes and expressing only a subset of genes required for persistence. Latent bacteria, like Mycobacterium tuberculosis in latent tuberculosis infection, reside in granulomas and are contained by the immune system without causing disease; they can reactivate if host defenses decline. Latency is also used to describe a stage in phage infection when viral genomes integrate into bacterial chromosomes as prophages (lysogeny) and replicate passively with the host until induced to enter the lytic cycle. In genetics, a latent trait or latent gene is one whose phenotype is not expressed unless specific conditions are met. The term also applies to latent periods in growth curves, where a delay exists between infection and the onset of replication or between stimulus and response. Environmental factors, immune surveillance and epigenetic regulation contribute to maintaining and breaking latency. Understanding latency is critical for disease control because latent reservoirs evade therapy and can seed future outbreaks.
Contexts and examples
• Herpes simplex virus type 1 remains latent in trigeminal ganglia neurons and can reactivate, causing cold sores.
• Varicella zoster virus establishes latency in dorsal root ganglia after chickenpox; reactivation leads to shingles.
• Latent tuberculosis infection occurs when M. tuberculosis persists in a non‑replicating state within granulomas and causes no symptoms.
• Temperate bacteriophages exhibit latency during lysogeny by integrating into the bacterial chromosome.
• Latent traits in Mendelian genetics refer to recessive alleles that do not manifest in heterozygotes but may be inherited by offspring.
Latent states represent hidden phases of microbial life cycles or genetic traits that can become active under specific conditions. Recognizing latency helps predict reactivation risks and informs therapeutic strategies.
Related Terms: latency, lysogeny, dormancy, reactivation, persistent infection