Herpes Simplex Type I Virus - Essay Example

Herpes Simplex Type I Virus Introduction This paper presents a case study of an infectious disease, Herpes Simplex Type I virus, giving an account of its aetiology, the impact of the disease in both global and local terms, and a description of its transmission processes. The paper then moves on to look at factors influencing its transmission rate, infection methods in the population most at risk, and whether there are any groups that are at particular risk. The control methods currently in use are discussed, and a discussion of why particular control methods are not successful is entered in to. A comparison of the Herpes Simplex type I virus disease dynamics and control with these factors for other diseases is then presented, with the particular diseases to be studied including influenza, schistosomiasis, malaria, measles, CJD, pinworm/roundworm/hookworm, Chinese liver fluke, elephantiasis, river blindness, Aids, and influenza. In terms of comparing Herpes Simplex Type I virus with the other diseases listed, the following factors will be considered: mode of transmission (i.e., indirect or direct) rate of infection, immunity, vaccines, treatment, diseases prevalent in developing countries, diseases prevalent in developed countries, (global distribution) diseases which affect mainly children, whether highly infectious or not so highly infectious; epidemic or endemic. The virus and its characteristics will then be compared with the Herpes Simplex Type II virus, and the Epstein-Barr virus, and Conclusions as to its likely future impact will be presented. Aetiology of the Disease The Herpes Simplex Type I virus, or the cold sore virus, marks its presence through the appearance of blisters on the skin near the mucous membranes (i.e., mouth/genitals). The Herpes Simplex Type I virus symptoms are contagious, and are not currently curable. It is thought that once a person has been infected with Herpes Simple Type I virus, many factors can trigger a recurrent infection, such as stress, or exposure to the sun; researchers have suggested that antibiotic use can also trigger recurrent infections, as they lower the bodies immune system's ability to cope with the virus, and so the virus escapes the nerve ganglia (where it usually resides when dormant) and causes an outbreak of sores. Impact of the Disease in both Global and Local Terms Herpes Simplex Type I virus is thought to be prevalent worldwide, but this fact is difficult to measure exactly due to the fact that it lies dormant in hosts the majority of the time. In terms of local impacts, the symptoms of the disease need treating, otherwise they cause discomfort, embarrassment and even depression amongst sufferers, which can lead to larger health concerns. The treatment of Herpes Simplex Type I virus is therefore widely available, over the counter, for example, in the developed world. It is said that the symptoms of Herpes Simplex Type I virus are the anxiety of the rich; the poor and people living in the developing world live with the symptoms as a minor ailment. Description of the Transmission Processes of the Disease Herpes Simplex Type I virus is transmitted through skin-to-skin contact, especially if the contact is made through skin that has tiny ruptures in its surface. It was previously thought that the virus was only transmitted during an outbreak of symptoms, but recent research has shown that the virus can be transmitted skin-to-skin in periods when no symptoms are present. The usual incubatory period for skin-to-skin transmission of the virus when its symptoms are present is 3 days; when no symptoms are present, this increases to 11 days. Analysis of the Factors Influencing Transmission Rates Many factors can influence the transmission of Herpes Simplex Type I virus, including: the use of condoms when an outbreak is present, to avoid transmission of the virus to the genital areas, use of the anti-viral drugs (see below), use of lip protectants when in the sun, managing stress patterns if you are known to be a carrier of the virus, managing sleeping patterns if you are known to be a carrier of the virus, and avoidance of transmitting the virus to different body parts during an outbreak. Control Methods There are currently no 'cures' for Herpes Simple Type I virus, other than minimizing the likelihood of transmission, and the transmission rates of the virus. There are several medications that can help with this aim, including: acyclovir (known by its trade name Zovirax) and valacyclovir (known by its trade name Valtrex). These medications work by disrupting the pathway of thymidine kinase in the virus, effectively stopping the viral DNA replicating, cutting short its power to cause an outbreak. It has been recently suggested that lysine supplements could provide a complementary therapy for Herpes Simplex Type I viral treatment, as in vitro tests in tissue culture studies have shown that when the lysine: arginine ratio favours lysine, viral replication is suppressed. Research has also recently shown that derivatives from red seaweed, red wine and whey proteins can all be effective at stopping viral replication, at least in test on mice. Further research in to these potential control methods is ongoing. Comparison of the disease dynamics: Malaria Malaria is, unlike Herpes Simplex Type I, caused by a protozoan parasite, Plasmodium, and not a virus; the protozoan parasite is transmitted to humans by the female mosquito, Anopheles, and one particular strain of the parasite, Plasmodium falciparum, is fatal in the majority of cases. Malarial symptoms include fever, joint pain, vomiting and convulsions. The parasite is transmitted, as we have seen, by mosquitoes, who carry the parasite in their salivary glands; once a person is bitten by an infected mosquito, the parasites are transferred to their body, and travel to the liver, where they replicate in their millions, to cause the symptoms just described. Diagnosis of malaria takes place through inspection of a blood sample from the suspected patient, and treatment is via medication. In terms of prevention, there are several families of drugs that can be used to treat malaria, although it should be borne in mind that there is drug-resistance in several strains of Plasmodium; a vaccine for malaria is currently under development. Many people argue that the best form of prevention for malaria is to prevent mosquitoes from breeding, and many methods have been put forward to achieve this aim, such as spraying with DDT (subsequently found to be toxic to humans) and avoiding standing water, so that the mosquitoes cannot breed. Avoiding being bitten is also a way of preventing malaria, and there are many ways in which this can be effected, such as applying repellent. In terms of the distribution of malaria, it is worldwide, and kills many hundreds of thousands, if not millions of people each year, especially in sub-Saharan Africa (Bosley, 2005). The causative agents, transmission, prevalence and treatment of malaria thus differ significantly from those of Herpes Simplex Type I virus. Comparison of the disease dynamics: Measles Measles is, similarly to Herpes Simplex Type I, caused by a virus, but is spread through respiration, not skin-to-skin contact. It is highly contagious, with symptoms including fever and spotting on the skin. There is currently no treatment for measles, although if complications arise from the disease, such as diorrhea or encephalitis (common complications presenting in the developing world), then treatments are administered to deal with these symptoms. A vaccine is available for measles, and is routinely administered to children in the developed world; those in the developing world are not so fortunate, however, and many children in these countries continue to die of measles. Whilst the causative agent of measles is a virus, the transmission, prevalence and treatment of measles thus differ significantly from those of Herpes Simplex Type I virus. Comparison of the disease dynamics: CJD CJD (Creutzfeldt-Jacobs disease) is thought to be caused by a prion, unlike Herpes Simplex Type I, which, as we have seen, is caused by a virus. CJD is not prevalent worldwide, although it came to media attention through the 'mad cow' scandal in the UK. It is thought that the prion lives in the nervous system of animals, and when eaten, the prion is transferred to the new host. The symptoms of CJD include a slow degeneration of the nervous system, until the host is left in a coma-like state. CJD was first reported in some hill tribes in Papua New Guinea, where cannibalism is rife: the prion was obviously passed from human to human via the flesh they were eating. The causative agents, transmission, prevalence and treatment of CJD thus differ significantly from those of Herpes Simplex Type I virus. Comparison of the disease dynamics: Schistosomiasis Schistosomiasis (bilharzia) is caused by flatworms, not a virus, as with Herpes Simplex Type I. It is known that five species of flatworm cause schistosomiasis, all of which have a complex life cycle involving water snails. Schistosomiasis is prevalent mainly in developing countries in the tropics, and it is thought that the diease affects some 200+ million people worldwide. Schistosomiasis induce chronic symptoms, such as fever, fibrosis, hypertension and brain granulomas, which, in its worst cases, can cause central nervous system legions. Diagnosis of schistosomiasis is by identification of the flatworm in the urine or faeces, and treatment is by doses of a drug (praziquantel) that is known to be effective against the causative agent. It is thought that the best method of prevention, however, similarly to malaria, is trying to avoid the causative agent breeding or gaining access to ones body: this is achieved by avoiding water which contains the hosts of the flatworm i.e., the water snails, or by ensuring that the water snails are killed through use of chemicals before using the water. The causative agents, transmission, prevalence and treatment of schistosomiasis thus differ significantly from those of Herpes Simplex Type I virus. Comparison of the disease dynamics: Pinworm/Roundworm/Hookworm These are known as threadworms, and are not viral, unlike the Herpes Simplex Type I as previously discussed. Threadworms are most commonly found in young people, mostly children, where they are found living in the small intestine and colon; left untreated, they can cause enterobiasis. Common symptoms include itching, and sleep disturbance (due to the need to scratch), and treatment is easy through medication which is widely available. As with many of the diseases discussed, however, this medication is not available to many people in the developing world. The causative agents, transmission, prevalence and treatment of pinworm/roundworm/hookworm thus differ significantly from those of Herpes Simplex Type I virus. Comparison of the disease dynamics: Chinese Liver Fluke Chinese liver flukes are a type of flatworm, which are prevalent, worldwide, despite the connotations of the name. They cause many of the same symptoms as other 'worm' diseases, and can cause malnutrition in their hosts as they live in the digestive tract, and, as such, can take nutrients away from their host. Treatment is, as we have seen for many of these diseases discussed, easy with medication, but as we have seen, this medication is often not available in the developing world, leading to widespread cases of Chinese liver fluke being reported in these areas. The causative agents, transmission, prevalence and treatment of Chinese liver flukes thus differ significantly from those of Herpes Simplex Type I virus. Comparison of the disease dynamics: Elephantiasis Elephantitis, and its causes are interesting in that there are two forms of this disease: parasitic (lymphatic filariasis) and non-parasitic (non-filarial). Both forms cause intense swelling of the skin of the legs and genitals. The non-parasitic form is thought to be caused by contact with volcanic ash, whereas the parasitic form is caused by exposure to nematodes transmitted by mosquitoes. Upon entering the host, the nematode enters the lymph nodes and causes swelling; it is not currently known if the nematode itself invokes this reaction, or if its symbiotic bacteria Wolbachia causes the swelling. Elephantitis is extremely prevalent in tropical countries, with over 80 known to be affected by the disease, with a total of more than 130 million people. Treatment for this disfiguring disease has little effect if the disease is not caught early, and it is difficult to catch early, as there are little or no early warning signs; once the disease develops, the only course of action is managing the symptoms of the disease. The causative agents, transmission, prevalence and treatment of elephantitis thus differ significantly from those of Herpes Simplex Type I virus. Comparison of the disease dynamics: River Blindness River blindness is caused by a parasitic worm, Onchocerca, which can lay dormant in the host for decades. The parasitic worm is transmitted to the host by a fly, at the time the fly takes its meal, much like malaria transmission from the mosquito. River blindness, as the name suggests, causes blindness, and is widespread in many tropical countries, despite the fact that it can easily be treated by medication, such as mectizan. Interventions by many aid programs have attempted to eradicate this disease in Africa, through treatment with the medication, but the disease is still prevalent in many African, and other tropical, countries. The causative agents, transmission, prevalence and treatment of river blindness thus differ significantly from those of Herpes Simplex Type I virus. Comparison of the disease dynamics: Aids AIDS is the end-stage of the HIV virus, which is transmitted sexually, or through blood transfusions with contaminated blood. The HIV virus, of which there are many forms, and which mutates rapidly, is prevalent across the globe, but is controlled in some continents better than others. For example, in Europe, the spread of HIV is controlled by education, and HIV/AIDS symptoms are controlled by medication; in Africa the situation is not so rosy, and education is basic, at best, due to lack of resources or cultural barriers - treatment for HIV is also almost non-existent, due the prohibitive costs of medication in these countries, and the unethical practices of drug companies in these countries. Whilst the causative agent of HIV is a virus, in common with the Herpes Simplex Type I virus, the transmission, prevalence and treatment of HIV/AIDS differ significantly from those of Herpes Simplex Type I virus. Comparison of the disease dynamics: Influenza Influenza is caused by an RNA virus, and is prevalent in epidemic form across continents and decades; Europe experiences a flu epidemic every twelve years, on average. Influenza symptoms include fever, joint aches, fatigue and thirst. Prevention is through vaccination, and vaccinations are administered to 'at risk' groups in the developed world annually. Treatment, for those unvaccinated who contract the disease is through increasing fluid intake, and by administering anti-viral drugs. Influenza presents a particular problem as it is highly variable, with each form of the virus requiring different preventative measures; in this respect it is akin to HIV, which mutates rapidly. Whilst the causative agent of influenza is a virus, in common with the Herpes Simplex Type I virus, the transmission, prevalence and treatment of influenza differ significantly from those of Herpes Simplex Type I virus. Comparison of Herpes Simplex Type I virus with Herpes Simplex Type II virus The basic difference between Herpes Simplex Type I and Type II is that Type I causes cold sores, whereas Type II causes genital herpes. Both Types are transmitted by skin-to-skin contact, as we have seen, and Type II causes painful blisters not on the mouth, but on the genitals, along with pain when passing urine and excessive mucous production. Treatment for Type II is similar to Type I, i.e., with antiviral drugs which stop the virus replicating. Comparison of Herpes Simplex Type I virus with Epstein-Barr virus The Epstein-Barr virus is a member of the Herpes family of viruses, but unlike Herpes Simplex Type I and Type II, the Epstein-Barr virus is most usually asymptomatic, lying dormant in the B cells. Epstein-Barr can sometimes cause infections, known as mono (glandular fever), and it has been known, for a long time, to be a cancer-causing agent, implicated in the formation of breast cancer, for example (Epstein, 1964). Conclusions: Likely Future Impact of the Disease The long-term effects of being infected with, and living with infection with, Herpes Simplex Type I virus are not well known. It is known that the outbreaks of blisters caused by Herpes Simplex Type I virus can cause scarring, and it was thought for many years that this virus was responsible for cervical cancer in women. Pregnant women who are known to be carriers of Herpes Simplex Type I virus are recommended to take particular care: if they have an outbreak at the time of giving birth, the baby can become infected, and it is known that Herpes Simplex Type I virus can have serious consequences, including brain damage, or perhaps even death. Herpes Simplex Type I virus is a direct transmitted microparasite, and as such, the following formula can be used to describe its progress: R=NfL, where R is the rate of transmission; is transmission rate of disease, made up of frequency of host contact and infectiouness of the disease (i.e., essentially a measure of the extent to which contact results in infection); L is the average period of time over which host remains infectious; f is the fraction of hosts which survive long enough to become infectious themselves, and N is the number of susceptibles present in the population as a whole. With reference to the herpes simplex virus, it is likely that L would be limited, N would be high (80% of the world's population, as estimated by many researchers) and would be also be high. In this scenario, f would be 100% or close to 100% as the Herpes Simplex Type I virus is not fatal, and therefore close to 100% of its host would live. R, the measure of its progress is therefore high, compared to other diseases discussed in this paper, as for some other diseases, and situations, such as HIV in Africa, R will be relatively low, due to the high death rate presenting in this disease in this area, due to lack of treatment. Based on this formula and the known pathology of Herpes Simplex Type I, therefore, it is unlikely that Herpes Simplex Type I virus will lead to major worldwide health concerns, especially in view of the fact that there are routine treatments available, and that Herpes Simplex Type I virus simply does not kill in large numbers, unlike HIV, or influenza, for example. Conclusions In this paper, we have studied in particular the Herpes Simplex Type I virus and have discussed in detail its aetiology, its transmission, its prevalence, and prevention. We have compared the virus to other diseases, in particular to influenza, schistosomiasis, malaria, measles, CJD, pinworm/roundworm/hookworm, Chinese liver fluke, elephantiasis, river blindness, Aids, influenza, Herpes Simplex Type II and Epstein-Barr virus. We have seen, through the use of a formula that Herpes Simplex Type I virus is not likely to pose a significant threat to humans, due to its non-lethal pathology and simple treatment with widely available anti-viral drugs, which stop the virus replicating within the host. Bibliography Boseley, Sarah. (2005) "Malaria crisis may doom Africa progress, MPs say" The Guardian, 2005-06-09 Epstein MA, Achong BG, Barr YM. Virus particles in cultured lymphoblasts from Burkitt's lymphoma. Lancet 1964;1:702-703. Jones CA (2004). "Vaccines to prevent neonatal herpes simplex virus infection". Expert Rev. Vaccines 3 (4): 363-364. Leung DT, Sacks SL. (2003). "Current treatment options to prevent perinatal transmission of herpes simplex virus". 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