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Viral hepatitis

Causes and incidence

The major forms of viral hepatitis result from infection with the causative viruses: A, B, C, D, E, or G.
Type A hepatitis is highly contagious and is usually transmitted by the fecal-oral route. However, it may also be transmitted parenterally. Hepatitis A usually results from ingestion of contaminated food, milk, or water. Many outbreaks of this type are traced to ingestion of seafood from polluted water. In 2001, there were more than 10,000 acute cases of hepatitis A infection reported in the United States.
Type B hepatitis, once thought to be transmitted only by the direct exchange of contaminated blood, is now known to be transmitted also by contact with human secretions and feces. As a result, nurses, physicians, laboratory technicians, and dentists are frequently exposed to type B hepatitis, in many cases as a result of wearing defective gloves. Transmission also occurs during intimate sexual contact as well as through perinatal transmission. An estimated 200,000 new cases of hepatitis B virus (HBV) and 5,000 deaths from HBV occur annually in the United States.
Although specific type C hepatitis viruses have been isolated, only a small percentage of patients have tested positive for them — perhaps reflecting the test’s poor specificity. Usually, this type of hepatitis is transmitted through transfused blood from asymptomatic donors. Hepatitis C accounts for 30,000 new infections and 8,000 to 10,000 deaths each year in the United States. Most exposures (60%) occur through the use of illicit I.V. drugs. However, sexual transmission is responsible for 20% of cases. More than 170 million people have the hepatitis C virus worldwide.
Type D hepatitis is found only in patients with an acute or chronic episode of hepatitis B and requires the presence of HBsAg. The type D virus depends on the double-shelled type B virus to replicate. 
For this reason, type D infection can’t outlast a type B infection. About 15 million people are infected with hepatitis D worldwide. It’s more common in adults than in children. People with a history of illicit I.V. drug use and people who live in the Mediterranean basin have a higher incidence.
Type E hepatitis is transmitted enterically, much like type A. Because this virus is inconsistently shed in feces, detection is difficult. In the United States, the prevalence of hepatitis E is less than 2%. It’s typically found in developing countries that lie near the equator. Incidence is highest among people ages 15 to 40.
Type G may be transmitted in a manner similar to that of hepatitis C. It may also be transmitted by sexual contact, and its incidence may be higher than previously suspected. It’s associated with acute and chronic liver disease, but studies haven’t clearly implicated the hepatitis G virus as an etiologic agent.
Other proposed causative factors, such as non-ABCDE viral hepatitis and type F, are under investigation.
tags:hepatitis abcdefg,Causes and incidence, C hepatitis viruses, B infection,

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