HEPADNAVIRUS: CHARACTERISTICS, MORPHOLOGY, TREATMENT - BIOLOGY - 2025

The hepadnavirus are a group of viruses that are related family Hepadnaviridae with hepatitis B. Its genes, which are very small, and these are DNA viruses replicate using the mechanism called reverse transcription. At least 2 genera of these viruses are known to cause hepatitis B in humans, other mammals, and even birds.

The virus that attacks man has managed to cause more than 250 million chronic cases, of which about 20 to 40% will lose or lose their lives due to liver carcinoma or liver cirrhosis.

Virions or infective particles of the virus that causes hepatitis B (a hepadnavirus). Taken and edited from: CDC.

Taxonomy

According to the Baltimore system, which classifies viruses into seven groups based on the combination of DNA or RNA they have, replication methods and the presence of single or double chains, hepadnaviruses belong to group VII, in the so-called viruses of reverse transcription of DNA or virus dsDNA-RT (acronym in English).

The dsDNA-RT group is made up of two families, Caulimoviridae and Hepadnaviridae. Within the Hepadnaviridae (Hepadnavirus), two genera, Orthohepadnavirus and Avihepadnavirus, are known to date, affecting the liver system of a wide variety of species.

characteristics

Hepadnaviruses are DNA reverse transcription viruses, which means that they replicate their genes (genome) aided by a DNA polymerase-type enzyme called reverse transcriptase, which acts by synthesizing double-stranded DNA, using single-stranded RNA as a template.

They have very small genes made up of DNA that occurs in a single-stranded and a double-stranded portion.

An important characteristic of these viruses is that their genes are made of DNA and not RNA. They also synthesize DNA in the cell that has been infected, long before infectious particles are released. They have a very peculiar and unique type of RNA packaging mechanism in this type of virus.

They are viruses of worldwide distribution. They affect a significant number of vertebrate species including birds, mammals, and were recently discovered in fish. They are associated with different liver disorders and with various transmission mechanisms.

Morphology

In certain groups of mammals, especially laboratory mice, hepadnaviruses are known to be viruses with a very small size, with infectious complete viridid ​​particles of spherical shapes of about 40 to 48 nanometers.

The protein coat that covers and protects the viral genetic material is composed of 60 asymmetric units made of 4 types of proteins. It presents a circular double-stranded DNA molecule about 3.2 kb in size, with a single or single-stranded DNA part and a DNA-dependent DNA polymerase part.

Transmission

Hepadnaviruses have two general routes of transmission that are: by contact, which can be by bodily fluids (especially blood), and by vertical transmission from mother to baby.

Regarding fluids, the mechanisms or routes of transmission range from sexual contact, use of infected needles (due to drug addiction, tattoo parlors and cosmetic piercings, accidental needle sticks, etc.), to occupational accidents due to contact. with contaminated fluids.

Vertical transmission can occur before the fetus is born, during labor, or after delivery through breastfeeding.

In the Orthohepadnavirus genus, transmission can occur sexually, by blood and vertically. However, in Avihepadnavirus transmission occurs mainly vertically.

Replication cycle of the hepadnovirus that causes hepatitis B. Taken and edited from GrahamColm at English Wikipedia.

Some streaming stats

In the world it is known that there are more than 250 million cases, of which the majority are found in the Asian and African continents. More than ¼ of these 250 million people will die from liver cirrhosis or liver carcinoma.

It has been calculated that 0.5% of the population in developed countries suffers from hepadnavirus infections or is a carrier of these viruses.

One cubic centimeter of blood can carry more than 10 trillion infectious particles. These particles can remain infectious even in drops of blood that have dried more than 7 days ago.

Due to the resistance of infectious particles after some time has elapsed after the fluid or blood has dried, there is statistically a higher risk of contracting an infection with hepadnavirus than with HIV.

Pathogeny

In humans, the infection manifests itself in various ways, in many cases the symptoms are not specific or obvious. Initially, the disease incubates for long periods, approximately between a month and a half and four months.

During this period, the hepadnavirus replicates an enormous number of times (more than 10 billion virions or infectious particles / milliliter). At the end of the incubation phase, the infected person presents symptoms such as fatigue, general malaise, fever, and the skin and mucous membranes may even turn yellow (jaundice).

The infection can be classified as chronic or acute. It can take years to develop and can lead to liver cirrhosis and / or hepatocellular carcinoma. In adults the infection is more serious than in children.

Some organisms that have suffered from the disease become carriers, being able to produce virions for many years, and others never become carriers. Science is still debating the causes of these two situations without finding a conclusive answer.

Prevention

The main preventive elements would be to avoid sexual contact and to use sterile needles and equipment. The most effective, however, is the subunit vaccine for human hepatitis B virus, which consists of the genetically engineered HBsAg antigen.

Treatment

Some authors suggest that there is no specific treatment for infections caused by hepadnaviruses. On the other hand, others, on the other hand, coincide in several treatments such as massive doses of signaling proteins known as alpha and beta interferons.

The antiviral drug Lamivudine is another suggested treatment, which works by inhibiting the hepadnavirus enzyme transcriptase. At some point, doctors used the drug Fialuridine but due to its toxicity and the death of at least 5 people treated with this drug, they stopped prescribing it.

In very severe severe cases, liver or liver tissue transplantation is a good option to increase the patient's chances of survival.

References

1. Hepadnaviruses (HBV). Recovered from biologia.edu.ar.
2. Hepadnavirus. Recovered from ecured.cu.
3. Hepadnavirus. Recovered from britannica.com.
4. J. Hu & C. Seeger (2015). Hepadnavirus Genome Replication and Persistence. Cold Spring Harbor Perspectives in Medicine.
5. Retroviruses and Hepadnavirus. Recovered from bio.libretexts.org.
6. Hepadnaviridae. Recovered from viralzone.expasy.org.
7. Hepadnaviridae. Recovered from microbewiki.kenyon.edu.
8. Hepadnaviridae. Recovered from en.wikipedia.org