Virus and scientific name: Hepatitis B virus (HBV)
The only known natural hosts for the hepatitis B virus are humans. Although, other animals (ie. chimpanzees) have been able to host it in laboratory settings.
Usually, it will infect a human’s liver cells (hepatocytes), which causes our immune system to respond by targeting those infected liver cells, resulting in liver inflammation (hepatitis).
HBV is spread through direct contact with infected blood and body fluids (ie. semen). Since blood levels of HBV are high in infected persons - much higher than HIV -, it is easy to transmit.
The virus can be transmitted through having unprotected sex with an infected person. This will happen when semen, vaginal secretions, saliva, or blood, enter the body.
HBV is easily transmitted through needles and syringes contaminated with infected blood. Sharing intravenous (IV) drug paraphernalia puts you at high risk of hepatitis B due to exposure to blood and unsanitary conditions.
Accidental needle sticks:
Through contact with infected human blood.
Infected pregnant women can pass on the virus during childbirth. However, newborns can be vaccinated to prevent transmission.
Unlike other viruses (ie. rhinovirus), you cannot be infected by the Hepatitis B Virus through being around infected persons who may sneeze or cough, or having casual contact (ie. shaking hands) with them. Kissing or being breastfed by an infected person will also not caused the virus to be transmitted unless they are open sores or cuts. Transmission through the sharing of food or water is also not possible.
Sub-saharan Africa and East Asia - most prevalent (between 5–10% of the adult population is chronically infected)
Central and Southeast Asia
Western Europe and North America (Less than 1% of the population chronically infected)
People at greatest risk for HBV infection are:
people who have multiple sex partners
men who have sex with men
infants born to infected mothers
Children under 6 years of age are most at risk for chronic infection of the hepatitis b virus.
In the U.S., hepatitis B is most common in people ages 25 to 44.
Approximately 350 million people worldwide are infected with HBV.
HBV is a noncytopathic virus. This means that the virus itself does not cause direct damage to liver cells. Instead, it is the immune system’s aggressive response to the virus that usually leads to inflammation and damage to the liver (hepatitis). However, it can cause damage to liver cell’s genetic material.
HBV leads to a wide spectrum of liver disease ranging from acute hepatitis (including fulminant hepatic failure) to chronic hepatitis, cirrhosis, and hepatocellular carcinoma (HCC). Symptoms can take two to six months to appear and only about 50 percent of people develop symptoms (even though damage can already be done to your liver).
There are usually two types of infection:
1. Acute - lasts less than six months
Most people do not have any symptoms during this phase (asymptomatic acute hepatitis - like our poor virus friend), however some may have an acute illness that lasts many weeks (symptomatic acute hepatitis) with symptoms of:
Yellowing of your skin and the whites of your eyes (jaundice)
Rare - acute liver failure
About 95 percent of adults will recover within 6 months of becoming infected with acute hepatitis B and as a result will develop lifelong protection against it (due to antibodies). The remaining 5 percent are unable to clear the virus and will become chronically infected.
2. Chronic - lasts six months or longer (or for a lifetime)
The risk for chronic hepatitis b is depends on age. The younger the age, the more likely that the infection will become chronic (<6 years old is at greatest risk).
Mild liver disease - no long term morbidity or mortality.
Active disease - can progress into cirrhosis (scarring of liver) and liver cancer. There is also possibility of kidney disease, inflammation of blood vessels and anemia.
Around 1/3 of the people with chronic HBV infection will ultimately develop a long-term consequence of the disease, such as cirrhosis, end-stage liver disease, or HCC.
For people with severe chronic hepatitis and cirrhosis, the 5-year survival rate is about 50%.
There are eight different types/genotypes of HBV, labeled: A-H. However in 2014, 2 more types have been found, labeled: A-J. The differences between the genotypes are based on differences in HBV’s genetic structure.
HBV genotypes B and C are common in Asia
Genotypes A and D occur frequently in Europe.
Genotypes F and H are found in Central and South America.
US: see genotypes A, B, C, and D.
Finding out the HBV genotype may have some value when choosing treatments for hepatitis B. But there is debate over whether or not knowing the genotype is important.
The HBV undergoes the lysogenic cycle to reproduce.
The virus gains entry into the liver cell (hepatocyte) by binding to a receptor on the surface of the cell and enters it.
Then, the viral capsid delivers the viral genome (relaxed circular DNA, rcDNA) to the nucleus where it is converted by host enzymes into cccDNA, which functions as a mini-chromosome.
The cccDNA mini-chromosome then serves as template for the production and replication of new viral components.
The HBV Core protein accumulates in the cytoplasm where it is used to make the new copies of the genome and to make the capsid core protein and the viral DNA polymerase.
Capsid assemblies with either leave as new infectious viral particles or return to the infected nucleus, continuing the cycle and prolonging infection.
Two HBV vaccines are available: Recombivax HB and Engerix-B.
All infants should get the vaccine within 24 hours, followed-up by 2 or 3 doses to complete the primary series.
The complete vaccine series induces protective antibody levels in more than 95% of infants, children and young adults. Protection lasts at least 20 years and is probably lifelong.
It is 95% effective in preventing infection and the development of chronic disease and liver cancer due to hepatitis B.
Avoid sharing needles/syringes, spoons, drug solutions or water, filters, cookers, pipes, straws used for snorting drugs, and other drug related equipment.
Safe sex: Use condoms/dental dams to reduce the risk of acquiring HBV.
Sterile Equipment: Avoid dental, medical or cosmetic procedures that penetrate the skin (ie. tattooing) unless you are certain that the needles, materials and equipment are sterile.
Wear personal protective equipment (ie. latex gloves) when in contact with someone else’s blood or bodily fluids.
Don’t share personal items like razors, scissors, nail clippers or toothbrushes.
Take all precautions when travelling to countries with high rates of HBV infection.
Treatment to prevent infection after exposure:
Get an injection of hepatitis B immune globulin within 12 hours of coming in contact with the virus may help stop development of infection. You can get this even if you are previously vaccinated.
Treatment may not be needed. Simply rest and take in adequate nutrition and fluids while your body fights the infection.
Take antiviral medications: lamivudine (Epivir), adefovir (Hepsera), telbivudine (Tyzeka) and entecavir (Baraclude). They can help fight the virus and slow its ability to damage your liver.
Interferon alfa-2b (Intron A) is a synthetic version of a substance produced by the body to fight infection. Take this if you do not want to undergo long-term treatment, or want to get pregnant in the near future. Side effects may include depression, difficulty breathing and chest tightness.
Get a liver transplant. This is only if your liver is severely damaged beyond realistic salvation.
Currently, there are other drugs in development.
Hepatitis B infections have declined substantially since 1991 when a strategy to eliminate HBV transmission through immunization was started.
It is one of a few known non-retroviral viruses. They use reverse transcription as a part of its replication process.
HBV can survive without a host for 7 days and still be capable of causing infection.
An estimated 240 million people are chronically infected with hepatitis B.
More than 686 000 people die every year due to complications of hepatitis B, including cirrhosis and liver cancer.
The hepatitis B virus is 100 times more infectious than HIV, the virus that causes AIDS.