Introduction:
The symptoms of liver involvement can range from being asymptomatic to conditions leading to hepatic (liver) failure. Loss of control in the immune system is responsible for hepatitis (liver inflammation) associated with opportunistic viral infections.
What Are the Viral Infections That Can Affect the Liver?
A. Influenza:
It is an infection in the nose, throat, and lungs. It is commonly called the flu virus. This virus causes a self-limiting respiratory infection that usually presents with fever, rhinorrhea (runny nose), sore throat, and occasional gastrointestinal symptoms. The liver enzymes, such as aminotransferase levels, remained unperturbed and were not noted much. In 2004, during the H1N5 influenza outbreak, almost sixty percent of patients with pneumonia (an infection in the air sacs of the lungs) had deranged liver function test values and some gastrointestinal symptoms, such as vomiting, abdominal pain, and diarrhea.
Some autopsies also revealed hepatic centrilobular necrosis (cell death occurring in the center of the lung's functional unit, otherwise called the secondary pulmonary lobules). But no antigen or viral detection could cause liver disease. Thus, the damage done to the liver in the patients dying from influenza has been immune-mediated, as there were also high levels of cytokines (small proteins that are significant in controlling the growth and activity of immune cells). It has been proposed that immune-mediated liver damage may have been the cause of elevated liver enzymes in other viral respiratory infections.
B. Coronavirus (Severe Acute Respiratory Syndrome):
It is also called SARS-CoV (severe acute respiratory syndrome coronavirus) and results from severe lung and gastrointestinal infections. There was also the involvement of other organs in this infection. Twenty-five percent of patients had elevated liver enzymes when the infection occurred, and another forty-five percent of patients with normal liver enzyme levels will initially develop it at later stages. Overall, seventy percent of patients had elevated liver enzymes in the presence of infection. Jaundice was also observed at a minimal level of less than ten percent. In most patients, aminotransferase levels were observed to rise toward the end of the first week and peak at the end of the second week. After the disease was treated, most patients' aminotransferase levels returned to normal. In cases of severe liver damage, the level of alanine transaminase levels raised more than five times the upper limit, which was more frequently observed in male patients. Histological studies revealed a significant cell death of the liver cells. The liver cells also showed ballooning, and lymphocytic infiltration was found in the portal tracts and liver lobules.
C. Measles:
It is a viral infection caused by a highly contagious virus. It is an airborne disease that spreads easily from one person to another when infected individual coughs or sneezes. The Morbillivirus of the Paramyxoviridae family causes it. It is an acute illness with a typical rash that vaccinations can prevent. The symptoms usually develop ten to twelve days after exposure to an infected person, lasting for seven to ten days. The initial symptoms include a fever greater than 104 degrees Fahrenheit, cough, runny nose, and inflamed eyes. Small white spots called Koplik’s spots can form inside the mouth two to three days after the symptoms start. It is associated with diverse complications such as pneumonitis or subacute sclerosing panencephalitis (a progressive neurological disorder of children and young adults affecting the central nervous system).
Hepatic abnormalities have been observed more frequently in adult patients with primary infection than in children. Two patterns of hepatic dysfunction have been noted. Elevating liver enzymes aminotransferases without showing symptoms resolve within a few days, and rarely prolonged cholestasis (flow of bile from the liver stops) and jaundice (yellowing of the skin and white part of the eyes) can occur when measles begin to reside. In liver tissue, steatosis (having too much fat build up in the liver), liver inflammation, and focal necrosis (cell death of a cluster of liver cells) have also been observed.
D. Enterovirus:
Group B coxsackievirus infection can cause liver disease as a part of the infection affecting various organs in young children and rarely in adults. Histology of the liver shows hemorrhagic necrosis (cell death accompanied by bleeding) in newborns. However, in adults, swollen hepatocytes (liver cells), biliary stasis (slow movement of the bile flow), and a mixed infiltrate of mononuclear and polymorphic leukocytes (blood cells made in the bone marrow and found in the blood and lymphoid tissue) in the portal tracts and sinusoids are observed.
E. Parvovirus:
This virus is a common and highly infectious childhood infection characterized by a rash. It is otherwise termed slapped cheek disease due to the rash found on the face. It is also called the fifth disease since it was listed as the fifth most common childhood illness. In most children, the parvovirus infection is mild and needs little treatment compared to adults, where the infection can be serious. It can be a predisposing factor for health issues found in the fetus of a pregnant woman. The infection is also more serious in people suffering from anemia (reduced red blood cell count) or who have a compromised immune system. Most immunocompetent people with this infection will be asymptomatic and suffer from muscle pain and fever followed by rash and edema (swelling). There may be the presence of fetal infection during gestation, which causes hydrops fetalis (abnormal amount of accumulation of fluids in one or two areas of the body). Parvovirus B 19 has also been identified as a cause of liver failure with anemia.
F. Torque Teno Virus (TTV):
This virus belongs to a group of viral strains that are non-enveloped with a single-stranded circular DNA (deoxyribonucleic acid) genome. It is a virus found in pigs and is mainly transmitted by the fecal-oral route. The prevalence of these viruses is comparatively high. It is most commonly found in patients who get post-transfusion hepatitis. It is the inflammation of the liver that happens after the transfusion of blood and is not found in other forms of hepatitis. The clinical significance of torque teno virus (TTV) remains unclear. Research on chimpanzees with the infusion of TTVs led to viremia (virus in the blood) but did not cause hepatitis. Studies conducted on TTV transmission also failed to establish a relationship between torque teno virus (TTV) and elevated serum aminotransferase levels, which is a liver enzyme. It caused acute hepatitis in some patients, but studies could not prove the relation between TTV and hepatic histological abnormalities in studies conducted in clinics. Thus TTV cannot be considered an independent risk factor for liver disease but can be included along with other factors for the cause of liver damage.
Conclusion:
Thus, liver damage can be caused due to the presence of viruses that potentially cause infections in the system. These observations are of great significance for a better understanding of infections that can have an impact on the liver. In most infections, hepatitis is thought to be the consequence of an immune-mediated viral response that causes inflammation in the liver.
