The Threat Of The Human Hepatitis A Virus Biology Essay

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Countries like Russia have low levels of sanitation and poor personal hygiene, thus facilitating maintenance of diseases such as human hepatitis A virus. Human hepatitis A virus is one of the hepatitis viruses that affect the liver in humans. According to CDC website, endemicity of Hepatitis A virus in countries like Russia is intermediate, which means that this virus is constantly occurring in these regions, but at the intermediate level [8]. The paper will cover several major points of Hepatitis A virus such as: structure and classification, life cycle, disease, treatment, public health impact, and conclusion. Hepatitis A virus occurs largely in developing countries thus needs to be recognized and addressed.

Structure and Classification

Human hepatitis A virus is a causative agent of an acute infectious hepatitis A disease. It belongs to Baltimore group IV. HAV (which stands for hepatitis A virus) is classified under genera of hepatovirus and belongs to family of Picornaviridae [6]. It contains a linear positive sense, single strand RNA genome which will eventually code for a long polypeptide chain which then will be cleaved into structural and nonstructural viral proteins such as: VP2, VP3, VP1 structural proteins that will make up the capsid, VPg's, proteases for cleavage, and RNA dependent RNA polymerase for replication [4]. The genome is compacted inside an icosahedral capsid which is made out of numerous viral proteins. HAV is non-enveloped, thus indicating that its receptors are located on the surface of the capsid and implying that the virus is stable in the environment due to the fact that it does not have a lipid envelope [6]. The viral proteins are very important to hepatitis A virus because they help the virus establish, infect, replicate, and spread.

Life Cycle

Hepatitis A virus is one of the hepatitis viruses which are involved in infecting the liver cells which are known as hepatocytes [6]. As Understanding Viruses text books states, once a body is infected with hepatitis A virus, the virus is then travels to the liver via bloodstream and invades the hepatocytes [6]. Thus, hepatocytes are the cell tropism for hepatitis A virus because hepatocytes are the desired target of infection by hepatitis A virus. Since HAV is a positive single stranded RNA virus, it has a unique reproduction process. Once the virus reaches hepatocytes in the liver it will bind to huHAVcr-1 receptor located on hepatocytes [6]. After the virus is bound to a hepatocyte it will enter via basolateral domain of hepatocyte due to hepatocyte's polarity [7]. Then after entry, hepatitis A virus will uncoat and release its genome into the cytoplasm where it will express genes, replicate its genome, and assemble. According to WHO (world health organization site), HAV contains a large open reading frame that is spread along the whole RNA genome [4]. The open reading frame on the genome of the virus contains VPg-viral protein on its 5' end [4]. According to the Understanding Viruses text book, the VPg is bound to a no translated region (IRES) on the 5' end of the virus genome [6]. In addition, at its 3' end the genome of the virus contains poly A tail. The Understanding Viruses text book also states, that the IRES region of the viral genome has many functions such as: recognition of the RNA dependent RNA polymerase for translation and permission of the cap-independent translation of mRNA into a polyprotein chain [6]. The genome of the virus contains many genes that will be expressed into polyprotein chain. Since each hepatitis A virus is made up of plus strand single strand RNA, its genome will be treated as mRNA and translated into polyprotein chain by host ribosome immediately. This polyprotein chain contains structural proteins such as VPs and non structural proteins such as proteases, RNA dependent RNA polymerase [6]. The protein protease that has been coded by the virus will cleave the long polypeptide chain into individual proteins. After all the necessary viral proteins have been made, the virus's RNA dependent RNA polymerase will synthesize negative single strand RNAs which will then be used as a template to synthesize positive single strand RNAs by viral RNA dependent RNA polymerase to be assembled into the new virus particles [6]. Since this is RNA virus the assembly of the genome into the capsid will take place in the cytoplasm as did gene expression and genome replication. The assembly step will assemble the newly replicated positive single stranded RNA genomes into capsids that are composed of newly encoded viral proteins. After the assembly is finished, the new virion particles egressed from hepatocytes via basolateral domain of the hepatocytes and into the blood and bile where it will travel and potentially infect other hepatocytes or excreted through feces [7].

Disease

Hepatitis A virus which causes hepatitis A disease has fairly low pathogenesis level, thus does not cause liver damage unlike other hepatitis viruses. It appears that hepatitis A virus replicates very slowly in the infected cells and shows minor cytopathic effect on the phenotype of the infected cell [5]. Some of these minor cytophatic effects include more viral RNA synthesis present in the cell; build up of multilayered membranes in the cell, collection of virus in vacuoles, and degenerative rough endoplasmic [5]. Since hepatitis A virus replicates very slow, it also does a very poor job at shutting down infected cell natural functions, thus does not show alteration in function of the cell [5]. Once the virus particles leave the host cell it does not lyses the hepatocytes [2]. The hepatitis A disease can be asymptomatic or cause flue like symptoms in children and can also show symptoms in adults [2]. For the most part hepatitis A disease does not have long term consequences, except for the fact that some symptoms will come back after some time in low percentage of people and cause symptoms such as fever, fatigue, abdominal pain, nausea diarrhea, etc or its been noted that less than 1 percent of people might have a liver damage and will need an operation for liver transplant, but that appears extremely rarely [2]. For the most part, the body of the infected individual will get rid of the disease on its own. According to the journal article "Hepatitis A vaccine in the last-minute traveler," the natural clearance by immune system of HAV is a complex process, but it does involve factors such as, natural killer cells, leucocytes, Bcell, and cytotoxic Tcells [1].

Treatment

The number one treatment that is available against hepatitis A virus is HAV inactivated vaccine which is called Havrix [1]. Two doses of vaccines are required [4]. It is recommended that travelers that are traveling to countries where hepatitis A virus is an endemic problem should be vaccinated 4 weeks prior to traveling due to the fact that it takes 4 week for development of antibodies against hepatitis A virus [1]. Also, once the second dose of vaccine is administered by the individual it will provide the individual with immunity against the virus for 20 years [2]. Without treatment the hepatitis A disease in most adults will result in symptoms such as fever, fatigue, vomiting, and even jaundice [2]. In little children, if treatment is not applied, then hepatitis A disease can proceed asymptomatic or give flue like symptoms [2]. The prognoses of hepatitis A disease with treatment which is a vaccine will result in production of antibodies that will result in elimination of the virus if the person becomes infected [1]. Also according to WHO article the patient can be given immune globulins against hepatitis A virus, but only within the 2 weeks of infection in order to prevent acute phase of the disease and not really eliminate the disease [4]. Preventions against the virus include vaccination, hand washing, sanitation, high levels of hygiene, and careful food handling [2]. Such preventions need to be enforced in developing countries in order not to contract outbreaks of hepatitis a virus.

Public Health Impact

Hepatitis A virus causes endemic all over the world [3]. Developing countries such as Russia, Africa, and South America are the susceptible countries to be infected with this virus due to the fact that these countries maintain low sanitations levels, low levels of hygiene, and posses contaminated water [4]. Susceptible populations for contraction of hepatitis A virus are people that have never been exposed to hepatitis A virus, people that have never received a vaccine for hepatitis A virus, and people that are immunocompromised-AIDS patients [4]. Hepatitis A virus posses several risk factors such as resistance to the environment such as change in temperature or ph, accumulation of low levels of sanitations throughout larger areas of the world, and accumulation of feces around areas that are contaminated with newly synthesized viruses of hepatitis A [4]. These risk factors can result in a wider and rapid spread of the virus worldwide if improvement of sanitation is not enforced. According to the WHO article there are constant outbreaks of hepatitis A virus due to the fact that even though some areas are recovered from poor sanitation, there are still areas that are not and are very susceptible to infection [4]. Thus, a sporadic outbreak of hepatitis A virus has been seen worldwide. Also WHO article states that in 1988 in Shanghai there was a large mollusk linked epidemic that resulted in 300,000 people getting sick from that particular seafood [4]. The WHO article also writes that the world experiences 1.4 million of hepatitis A virus infections annually [4]. The hepatitis A virus also impacts the world's economic aspect. The adults miss at least 30 days from work which puts a dent on the productivity, and kids miss school because of the flue like symptoms that they experience during the infection [4]. In addition, vaccines are somewhat expensive which are $40 per dose, as well as antibody detection test is $43 per case [4].

Conclusion

Hepatitis A virus is a widespread virus throughout the world especially in developing countries due to poor sanitation. The virus infects liver cells and can result in symptoms such as fever, fatigue, vomiting, even jaundice in adults or it can be asymptomatic in children or cause nonspecific flue like symptoms. The virus is a picornavirus, thus it is a positive single stranded RNA virus that has unique replication cycle in the cytoplasm of hepatocyte cells involving VPg, IRES, and various viral proteins. The disease itself has a very slow replication cycle; it takes a long time for the virus to produce new viruses. The virus also is almost incapable of shutting off the host machineries, thus does not lyses the cells once exits. The most important treatment and prevention against hepatitis virus A is the vaccine. The vaccine produces antibodies that fight the infection. The virus has a large impact on the public health because it is contagious and can infect everyone. The virus puts a damp on the economic aspect of the world, due to the fact that it is somewhat costly to be vaccinated, or have a detection test performed. Overall the hepatitis A virus is a very important virus that needs to be addressed in the developing countries and a vaccine needs to be administered persistently. I think that a better education on this virus will help the world to slowly move towards someday eradication the virus.

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