Editing Viral load (section)

{{short description|Amount of virus found in host tissue}}
{{Expert needed|1=Medicine|reason=Uncited "how to" content should be reviewed & article would generally benefit from expansion|date=January 2020}}
'''Viral load''', also known as '''viral burden''', is a numerical expression of the quantity of virus in a given volume of fluid, including biological and environmental specimens. It is not to be confused with '''viral titre''' or '''viral titer''', which depends on the assay. When an assay for measuring the infective virus particle is done (Plaque assay, Focus assay), '''viral titre''' often refers to the ''concentration'' of infectious viral particles, which is different from the ''total'' viral particles. Viral load is measured using body fluids [[sputum]]<ref name="wolfel20">{{cite journal |doi=10.1038/s41586-020-2196-x|title=Virological assessment of hospitalized patients with COVID-2019|year=2020|last1=Wölfel|first1=Roman|last2=Corman|first2=Victor M.|last3=Guggemos|first3=Wolfgang|last4=Seilmaier|first4=Michael|last5=Zange|first5=Sabine|last6=Müller|first6=Marcel A.|last7=Niemeyer|first7=Daniela|last8=Jones|first8=Terry C.|last9=Vollmar|first9=Patrick|last10=Rothe|first10=Camilla|author-link10=Camilla Rothe |last11=Hoelscher |first11=Michael |last12=Bleicker |first12=Tobias |last13=Brünink |first13=Sebastian |last14=Schneider |first14=Julia |last15=Ehmann |first15=Rosina |last16=Zwirglmaier |first16=Katrin |last17=Drosten |first17=Christian |last18=Wendtner |first18=Clemens |journal=Nature|volume=581|issue=7809|pages=465–469|pmid=32235945|bibcode=2020Natur.581..465W|doi-access=free}}</ref> and [[blood plasma]].<ref name=puren10/> As an example of environmental specimens, the viral load of [[norovirus]] can be determined from run-off water on garden produce.<ref name="shaheen19">{{cite journal |doi=10.1007/s11356-019-05435-0|title=Quantitative PCR-based identification of enteric viruses contaminating fresh produce and surface water used for irrigation in Egypt|year=2019|last1=Shaheen|first1=Mohamed N. F.|last2=Elmahdy|first2=Elmahdy M.|last3=Chawla-Sarkar|first3=Mamta|journal=Environmental Science and Pollution Research|volume=26|issue=21|pages=21619–21628|pmid=31129895|bibcode=2019ESPR...2621619S |s2cid=167210903}}</ref> [[Norovirus]] has not only prolonged [[viral shedding]] and has the ability to survive in the environment but a minuscule [[infectious dose]] is required to produce infection in humans: less than 100 viral particles.<ref name="robilotti15">{{cite journal |doi=10.1128/CMR.00075-14|title=Norovirus|year=2015|last1=Robilotti|first1=Elizabeth|last2=Deresinski|first2=Stan|last3=Pinsky|first3=Benjamin A.|journal=Clinical Microbiology Reviews|volume=28|issue=1|pages=134–164|pmid=25567225|pmc=4284304}}</ref>

Viral load is often expressed as viral particles, (virions) or infectious particles per mL depending on the type of assay. A higher viral burden, titre, or viral load often correlates with the severity of an active [[virus|viral]] infection. The quantity of virus per mL can be calculated by estimating the live [[Virus quantification|amount of virus]] in an involved fluid. For example, it can be given in [[RNA]] copies per millilitre of blood plasma.

Tracking viral load is used to monitor therapy during chronic viral infections, and in immunocompromised patients such as those recovering from [[bone marrow]] or solid [[organ transplantation]]. Currently, routine testing is available for [[HIV]]-1, [[cytomegalovirus]], [[hepatitis B]] virus, and [[hepatitis C]] virus. [[Viral load monitoring for HIV]] is of particular interest in the treatment of [[people with HIV]], as this is continually discussed in the context of [[management of HIV/AIDS]]. An undetectable viral load does not implicate a lack of infection. HIV positive patients on long-term combination antiretroviral therapy may present with an undetectable viral load on most clinical assays since the concentration of virus particles is below the [[limit of detection]] (LOD).