Viremia

SignSymptom infobox
Name = PAGENAME


Caption =
DiseasesDB =
ICD10 =
ICD9 = ICD9|790.8
ICDO =
OMIM =
MedlinePlus =
eMedicineSubj =
eMedicineTopic =
MeshID = D014766

Viremia (UK: viraemia) is a medical condition where viruses enter the bloodstream and hence have access to the rest of the body. It is similar to "bacteremia", a condition where bacteria enter the bloodstream.cite book | author = Ryan KJ, Ray CG (editors) | title = Sherris Medical Microbiology | edition = 4th ed. | publisher = McGraw Hill | year = 2004 | pages = 881 | isbn = 0838585299]

Primary versus Secondary

Primary viremia refers to the initial spread of virus in the blood from the first site of infection.

Secondary viremia occurs when primary viremia has resulted in infection of additional tissues via bloodstream, in which the virus has replicated and once more entered the circulation.

Usually secondary viremia results in higher viral shedding and viral loads within the bloodstream due to the possibility that the virus is able to reach its natural host cell from the bloodstream and replicate more efficiently than the initial site [Cerino A, Bissolati M, Cividini A, Nicosia A, Esumi M, Hayashi N, Mizuno K, Slobbe R, Oudshoorn P, Silini E, Asti M, Mondelli MU. "Antibody responses to the hepatitis C virus E2 protein: relationship to viraemia and prevalence in anti-HCV seronegative subjects." J Med Virol. 1997 Jan;51(1):1-5.] . An excellent example to profile this distinction is the rabies virus [Lodmell DL, Dimcheff DE, Ewalt LC. "Viral RNA in the bloodstream suggests viremia occurs in clinically ill rabies-infected mice." Virus Res. 2006 Mar;116(1-2):114-8. Epub 2005 Oct 19.] . Usually the virus will replicate briefly within the first site of say the bite of a rabid dog, within the muscle tissues. Viral replication then leads to viremia and the virus spreads to its secondary site of infection, the CNS. Upon infection of the CNS, secondary viremia results and symptoms usually begin [Gribencha SV, Barinsky IF. "Viraemia in rabies." Acta Virol. 1982 Jul;26(4):301.] . Vaccination at this point is useless, as the spread to the brain, leading to death, is unstoppable (the only clinical exception is Jeanna Giese). Hence vaccination must be done before secondary viremia takes place for the individual to be saved.

Active versus Passive

Active viremia is caused by the replication of viruses which results in viruses being introduced into the bloodstream. Examples include the measles, in which primary viremia occurs in the epithelial lining of the respiratory tract before replicating and budding out the cell basal layer, resulting in viruses budding into capillaries and blood vessels [Mulupuri P, Zimmerman JJ, Hermann J, Johnson CR, Cano JP, Yu W, Dee SA, Murtaugh MP. "Antigen-Specific B-cell Responses to Porcine Reproductive and Respiratory Syndrome Virus Infection." J Virol. 2007 Oct 17] .

Passive viremia is the introduction of viruses in the bloodstream without the need of active viral replication. Examples include direct inoculation from mosquitoes, through physical breaches or via blood transfusions [Lai CJ, Goncalvez AP, Men R, Wernly C, Donau O, Engle RE, Purcell RH. "Epitope determinants of a chimpanzee dengue virus type 4 (DENV-4)-neutralizing antibody and protection against DENV-4 challenge in mice and rhesus monkeys by passively transferred humanized antibody." J Virol. 2007 Dec;81(23):12766-74. Epub 2007 Sep 19.] .

See also

* septicemia
* Viral shedding

References