Acute viral infections

102961732_223f281698_mAn acute viral infection is characterized by rapid onset of disease, a relatively brief period of symptoms, and resolution within days. It is usually accompanied by early production of infectious virions and elimination of infection by the host immune system. Acute viral infections are typically observed with pathogens such as influenza virus and rhinovirus. Ebola hemorrhagic fever is an acute viral infection, although the course of disease is unusually severe.

Often an acute infection may cause little or no clinical symptoms – the so-called inapparent infection. A well-known example is poliovirus infection: over 90% are without symptoms. During an inapparent infection, sufficient virus replication occurs in the host to induce antiviral antibodies, but not enough to cause disease. Such infections are important for the spread of infection, because they are not easily detected. During the height of the polio epidemic in the US, the quarantine of paralyzed patients had no effect on the spread of the disease,  because 99% of the infected individuals had no symptoms and were leading normal lives and spreading infection. Inapparent infections probably are important features of pathogens that are well-adapted to their hosts. They replicate sufficiently to ensure spread to new hosts, but not enough to damage the host and prevent transmission.

Acute infections begin with an incubation period, during which the genomes replicate and the host innate responses are initiated. The cytokines produced early in infection lead to classical symptoms of an acute infection: aches, pains, fever, malaise, and nausea. Some incubation periods are as short as 1 day (influenza, rhinovirus), indicating that the symptoms are produced by local viral multiplication near the site of entry. For some infections, incubation periods can last many days (papilloma, 50-150 days) or even years (AIDS, 1-10 years). In these infections, the symptoms are likely produced by virus- or immune-induced tissue damage far from the site of entry.

An example of a classic acute infection is uncomplicated influenza. Virus particles are inhaled in droplets produced by sneezing or coughing, and begin replicating in ciliated columnar epithelial cells of the respiratory tract. As new infectious virions are produced, they spread to neighboring cells. Virus can be isolated from throat swabs or nasal secretions from day 1 to day 7 after infection. Within 48 hr after infection symptoms appear; these last 3 days and then subside. The infection is usually cleared by the innate and adaptive responses in 7 days. However, the patient usually feels unwell for several weeks, a consequence of the damage to the respiratory epithelium, and the cytokines produced during infection.

Acute viral infections are responsible for epidemics of disease involving millions of individuals each year, such as influenza and measles. When vaccines are not available, acute infections are difficult to control – most are complete by the time the patient feels ill, and the virus has already spread to another host. This characteristic makes it exceedingly difficult to control acute infections in large populations and crowded areas (such as colleges, nursing homes, military camps). The outbreaks of norovirus gastroenteritis this winter – a classic acute infection – highlights the problem. Antiviral therapy cannot be used, because it must be given early in infection to be effective. There is little hope of treating most acute viral infections with antiviral drugs until rapid diagnostic tests are become available. But the point is moot – there are no antivirals for most common acute viral diseases.

The rapid clearance of acute viral infections is a consequence of robust host defenses. The same virus may cause a long-term, or persistent infection, in immunocompromised hosts. An example is norovirus infection, which is self-limiting in immunocompetent hosts, but causes a chronic infection in immunosuppressed kidney transplant recipients. We will consider the characteristics of persistent viral infections in another post.

Westhoff, T., Vergoulidou, M., Loddenkemper, C., Schwartz, S., Hofmann, J., Schneider, T., Zidek, W., & van der Giet, M. (2008). Chronic norovirus infection in renal transplant recipients Nephrology Dialysis Transplantation, 24 (3), 1051-1053 DOI: 10.1093/ndt/gfn693

39 thoughts on “Acute viral infections”

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  3. If Antiviral therapy cannot be used, because it must be given early in infection to be effective, is there any other solution for this? I'm scared about it.

  4. CeBIT leidet unter der Krise – von raivo pommer

    – Die Zeichen der Krise sind allgegenwärtig. Auch die CeBIT in Hannover als größte Computermesse der Welt bleibt in diesem Jahr von der globalen Wirtschaftsflaute nicht verschont.

    Bereits vor einigen Jahren hatte – auch bedingt durch den wachsenden Wettbewerb mit anderen großen Messen – ein langsamer Ausstellerschwund eingesetzt. In diesem Jahr spitzte sich die Lage allerdings dramatisch zu. Insgesamt wird die Zahl der Aussteller um 25 Prozent einbrechen, lauten die jüngsten Schätzungen der Deutschen Messe AG. Die Ausrichter hoffen nun, für die Branche ein Signal des Aufbruchs zu setzen und Wege aus der Krise aufzeigen zu können.

    Angesichts der Weltwirtschaftskrise seien auch 4300 Aussteller immerhin ein noch Erfolg, heißt es aus Hannover. Das Gros der Aussteller, die der Messe in diesem Jahr fernbleiben, seien vor allem kleinere Hersteller aus Asien. Die wichtigsten großen Unternehmen würden aber wieder nach Hannover kommen. Allerdings bleiben der Messe in diesem Jahr tatsächlich auch Schwergewichte wie Samsung oder Toshiba fern. Zugleich wollen die CeBIT-Macher unter dem Stichwort “Webciety” (Kunstwort aus “Web” und “Society”) auch kleine und größere Unternehmen aus der Internet-Branche anlocken, die bislang nicht zu den traditionellen Ausstellern zählen.

    “Die Hightech-Industrie steht im Vergleich zu vielen anderen Branchen noch recht gut da”, sagt Bernhard Rohleder, Hauptgeschäftsführer des Branchenverbands BITKOM. Der Informationstechnologie- und Kommunikationsbranche komme bei der Bewältigung der Krise derzeit auch eine Schlüsselrolle zu. Viele kleine und große Unternehmen investieren gerade jetzt in neue IT- Systeme, um Kosten zu senken und in der angespannten Geschäftssituation weiter konkurrenzfähig zu bleiben.

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  7. i am working on molecule which is basically act on base of virus i.e.(suger or phosphates or nitrogen) which replaces very fast in just few minutes and with temporary side effects.BUT NOT ORGANIC FORMULATION.ITS MADE WITH BIOLOGICAL CATALYST ON NATURAL EXTRACT.

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  9. I was diagnosed to have an “Acute Viral Influenza”. I'm just wondering if this counts as H1N1 or just and ordinary flu. Although my situation has signs that I have colds, dry cough, painful joints and very sensitive skin when touched (it hurts a little) and a feverish feeling. What are the ways to find out if it is already H1N1? Hope you can help me out…

  10. The only way to know is to have a diagnostic test run in a health care
    provider's office. If you have influenza, it is likely the H1N1 strain
    which is predominating everywhere. However other respiratory viruses
    can cause similar symptoms, so without a lab test, it cannot be proven
    that you have influenza.

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  12. last week i have a sick and the doctor said it is acute viral infection in first idont know what is that and i ask my doctor and said i get that from my sorroundings from what i smell in my school.

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  15. And, the virology phrase of the day is: “inapparent infection”.

    Just think. Some viruses can replicate in a human host and spread throughout the environment infecting unsuspecting people.

    Some viruses. Some rna viruses. Some enteroviruses.

    And the CDC’s director, Dr. Thomas Frieden keeps telling us Ebola can’t be spread unless the host has symptoms.

    Really? And he knows this is 100% true, every time, every patient.

    We know for a fact that dogs can carry and shed Ebola virus and they don’t get sick.

    Is he telling me that 100 percent, ALL human immune systems function 100% exactly the same way and this, his, hypothesis has been proven beyond the shadow of a doubt?

    He seems to be. And he also keeps saying CDC/WHO know how to contain, control, prevent the spread of the epidemic, that they’ve done it before. He said that this past week, and last spring. About five countries and three continents ago.

    I think someone isn’t connecting the dots here.

    “So as not to cause a panic” goes the punchline of the old Russian cold war joke (joke being, what to do in case a nuclear attack is imminent? Put on your burial shroud and walk slowly to the cemetery. Why?)

    Maybe this is why Major Barrett was overheard talking to White House spokesmen about Ebola and he said “We’re fracked.”

    [My bona fides: physician, undergrad phi beta kappa regent’s scholar cum laude graduate, skeptic.]

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