Viremia

During the incubation period, which is the time between exposure to virus and appearance of symptoms, the following processes occur: implantation of the virus in susceptible cells, multiplication of virus at the site, shedding of the newly produced virus into the blood (primary viremia) and infection of distant susceptible organs to produce disease.

The entry of the virion into the body is not enough to cause infection. In order for the virus to cause disease, cells susceptible to the virus (i.e. possessing cell surface receptors capable of binding with and recognising the virus) must be present in the host and be easily accessible (i.e. not covered by physical barriers like mucus membranes or tissue barriers). Additionally, symptomatic disease will only set in if the host’s immune defence system can not prevent viral replication and a sufficiently high viral load is created that causes cellular organ damage by disrupting DNA synthesis or by consuming all of the cell’s nutrients and energy. Another factor that plays a critical role in viral disease is the virus’ virulence, meaning its ability to invade and propagate under genetically-determined strenuous circumstances (Ii.e. inflammatory cells, cytokines and the body’s natural interferons, etc).

Viral infection can be established in various ways, depending on which the viremias are characterized. The type of genetic material in the virus (single-stranded or double-stranded, RNA or DNA) dictates which of the following it is:

• Active viremia: Usually, after invading living cells, viruses fuse their genetic material with that of the host cell’s to encode proteins required for viral survival, propagation and multiplication.
• Passive viremia: Sometimes, viruses, having undergone their replicative cycle in an intermediate host (for example, the dengue virus transmitting Aedes mosquito), do not multiply after entering the human host but simply remain in the bloodstream. Many viral diseases transmitted by mosquitoes cause disease in a similar fashion.
• Primary viremia: The initial shedding of virus from the primary site of infection into the bloodstream. For example, with the measles virus, the primary infection occurs in the respiratory epithelium. Viral multiplication activity takes place exclusively in these cells, after which the newly produced viral particles enter the bloodstream.
• Secondary viremia: In some cases, after the viral infection has spread into the circulation from the primary site of infection, secondary infection is established in distant organs and tissues. Replicative activity reaches its peak in these secondary tissues, following which viral shedding in the bloodstream takes place. In such cases, the viral load of the disease tends to be greater as more viral particles are produced and shed. A classic example of such viremia is that caused by the rabies virus. Initial infection is followed by transmission of the viral activity to the brain tissue (central nervous system), at which point signs and symptoms appear. However, at that point it is too late to halt the progression of the virus, commonly leading to death.

Another important entity associated with viremia is viral sepsis.

Sepsis is defined as the dysregulated and exaggerated immune response of the body towards an infection. The resultant hyperinflammatory state produces widespread thrombosis (formation of blood clots by inappropriate activation of blood-clotting cells known as platelets), which blocks small blood vessels of organs, cutting off the oxygen supply and causing tissue death. Severe sepsis can result in extensive metabolic abnormalities, which cause disruption of the circulatory system and produce a marked fall in blood pressure; this is known as viral septic shock. Both sepsis and septic shock require treatment in the Intensive Care Unit (ICU). While bacterial sepsis and septic shock are more common, necessitating immediate administration of broad-spectrum intravenous antibiotics, nearly 40% of sepsis cases do not respond to them, indicating possible viral infection.

Risk factors for viral sepsis are:

• Neonatal sepsis: Viral infections with enteroviruses in babies during the first month of life can cause sepsis.
• Children under 5 years of age: Influenza virus infection can culminate in sepsis.
• Elderly over 65 years of age: Influenza virus can precipitate sepsis.
• Pregnant women: Pregnancy increases vulnerability to influenza-induced sepsis.
• Immunocompromised: Patients receiving immunosuppressant drugs or undergoing cancer treatment are at an added risk of contracting viral infections and experiencing sepsis.

While the specific signs and symptoms of viral diseases are based on the virus that causes it, most viral illnesses share a similar initial prodrome, wherein overall bodily secretions are increased.

Viral prodrome symptoms:

• Fever
• Headache
• Body aches
• Joint pain
• Diarrhea
• Rash
• Chills
• Fatigue
• Tender, enlarged lymph nodes

Viral sepsis: The presentation of sepsis in adults and older children can typically be as follows:

• Fever (body temperature higher than 38°C) or hypothermia (body temperature lower than 36°C)
• Chills and shivers
• Fast breathing
• Rapid heartbeat
• Confirmed infection anywhere in the body

Sepsis presents differently in younger children and neonatal sepsis can be deadly. Following are the signs you should look out for:

• Fever (body temperature greater than 38°C in babies under three months, or 39°C in those up to six months of age or if the child is apathetic) or hypothermia (body temperature below 36°C)
• Breathing may be accompanied by grunting, punctuated by pauses or leave the child unable to speak
• Cold extremities
• Baby unable to feed
• Repeated vomiting
• Lethargic or unconscious baby

Septic shock: Volume depletion due to excessive inflammation-induced fluid shift produces shock. Its symptoms can be:

• Dizziness or fainting spells
• Altered mental sensorium
• Slurred speech
• Nausea and vomiting
• Cold, clammy, mottled pale skin
• Severe muscle pain
• Severe breathlessness
• Reduced urine output than normal
• Diarrhea
• Loss of consciousness

Although virus-specific tests to detect viremia are available, clinical diagnosis is often most relied upon. Some chemical laboratory investigations are useful in isolating the virus and forming a diagnosis. Others detect the changes brought about by the viral infection.

Blood tests: Complete blood count, as an increase in lymphocytes is most often found in viral infections.

Immunological tests:

• Detecting antibodies: Most commonly with hepatitis B virus, antigens (HBsAg and HBeAg) and antibodies (Anti-HBsAg, Anti-HBeAg and Anti-HBcAg) in the serum provides invaluable information about the stage, duration and activity of disease to guide treatment. Other virus-specific antibody tests used to diagnose disease include the Paul Bunnell test for infectious mononucleosis caused by Epstein-Barr Virus.
• Rapid antigen tests: These are considered screening tests as they only detect the presence of the viral antigen. This means these kits can detect an infection if positive, but can not rule it out if negative.
• RT-PCR: Real-time polymerase chain reaction is a modality by which the genetic material (DNA or RNA) of a virus gets amplified for easier detection and diagnosis. This test is considered confirmatory, meaning a negative result implies a lack of infection.

Other tests:

• Viral culture: The suspected sample is introduced into a cellular medium. If the virus infects these cells and multiplies, the “culture” is considered positive.
• CD4+ cell count: CD4+ T helper cells get infected and destroyed by HIV virus; testing the count helps assess virus activity and load.
• Lumbar puncture: It may be done to test the cerebrospinal fluid for signs of viral infection in suspected meningitis.

Most viral infections are mild and self-limiting, needing little more than supportive management and symptomatic treatment.

Supportive management:

• Adequate rest
• Plenty of fluids, especially those with high electrolyte content (for example, coconut water, juices, etc)
• Gargles for sore throat
• Sponging for fever relief

Symptomatic medical management:

• Anti-inflammatory and pain medications (for headaches and body aches)
• Antiemetic or anti-nausea medications
• Antihistamines to reduce excessive nasal secretions (Read more: Runny nose)
• Anti-diarrheal medications
• Anti-itch creams, such as hydrocortisone creams
• Nasal decongestant medications and rinses
• Throat lozenges
• Cough syrups

(Read more: Home remedies for cough)

Disease-specific medical management: In some more serious viral infectious diseases like human immunodeficiency virus (HIV), daily triple-drug therapy is required lifelong to effectively suppress the viral load and thus symptoms.

• Antiretroviral therapy (ART): Daily lifelong triple-drug regimen comprising two nucleotide reuptake inhibitors and one non-nucleotide reuptake inhibitor. If the viral load isn’t suppressed well, second-line drugs are used. 
• Antiherpetic drugs: Herpes viruses cause cold sores on the mouth, genital warts, chickenpox, shingles and herpes zoster. Acyclovir is the most commonly used drug from this category. 
• Anti-hepatitis drugs: In order to effectively reduce viral load and prevent progression of chronic hepatitis infections (hepatitis B and hepatitis C) to liver cirrhosis or cancer, certain virus-specific drugs and interferon injections are available. 
• Anti-influenza drugs: Although most flu cases resolve on their own, virulent strains of H1N1 and H5N1 require a short course of drugs like oseltamivir (tamiflu) or zanamivir.

Viral sepsis and septic shock management: Intensive care unit (ICU) treatment with intravenous fluids (volume replacement), vasopressor agents (to raise blood pressure by compressing blood vessels) and bronchodilators (in case of acute respiratory distress syndrome) along with high flow oxygen may be administered.

Viremia can be prevented by the following measures:

• Ensuring up to date immunisation with vaccines against preventable viral diseases like measles, rubella, polio, hepatitis B virus and influenza
• Proper sanitation and hygiene
• Use of face masks, especially in large crowds or when experiencing symptoms
• Avoid coming in contact with high-touch objects and touching your face

(Read more: Homemade reusable masks)