Environmental and Geographic Factors That Cause Dengue Fever - Assignment Example

Running Head: DENGUE FEVER VIRUS (Name) (Course) (University) Date of presentation: Lecturer: Introduction Dengue fever is the most important arthropod-borne diseases and affects millions of people throughout the world each year. The fever is common in urban and semi-urban areas in different parts of the world. In the last few decades, dengue fever has spread considerably to most tropical countries and has become a major cause of hospitalizations and deaths. The Southern Pacific and South East Asia are some of the most densely affected regions. In these two regions, dengue hemorrhagic fever is a major cause of death among children. Dengue fever is caused by four different serotypes, all of which are transmitted by the Aedes aegypti mosquitoes. A major clinical spectrum for the fever ranges from asymptomatic infections to more severe forms such as dengue shock syndrome and dengue hemorrhagic fever. Clinical studies have shown that infection by one form of serotype results in permanent immunity but the serotype cannot offer protection against other serotypes (Gubler, Dengue & Monath, 2001). Environmental and geographic factors which cause dengue fever Several factors are known to influence the dynamics of mosquito populations and hence the transmission patterns of dengue fever in human populations. In particular, rainfall, humidity and temperature interfere in all stages of the vector’s development, from viability of eggs to the lifespan of adult mosquitoes and their dispersal in the environment. Additionally, various human factors such as poorly-planned urbanization, shakiness of water supply and garbage collection systems and high human population favor the proliferation of mosquito breeding sites and rapid spread of the infection (Johansen, 2002). Minimum temperatures have a great impact on the spread of the dengue fever disease through the life cycle of mosquito. During winter, low temperatures affect the survival of immature and adult mosquitoes (Chow et al, 1998). Similarly, lower temperatures assist larvae during winter to survive hence rapid spread of dengue fever disease. Incubation of the disease is also affected by temperatures. Lower temperatures greatly affect mosquitoes by shortening their lives for further transmission of the disease. Wind velocity is another factor which has an impact on the spread of dengue fever disease. When the velocity is low, mosquitoes tend to have frequent flights while when there is increase in wind velocity mosquito flight are suppressed thus making them not to move from one place to other. This reduces chances of spreading the disease from one person to another (Ritchie et al, 2002). Minimum humidity is also a factor that has great impact on the spread of dengue fever disease. When there is relative humility, spread of the disease reduces. This is because newly laid eggs are destroyed making the survival of mosquito larvae minimal. The adults get wet and this reduces their lifetime making them not to affect many people. Hence humidity has a great impact on the survival of mosquitoes. To a greater extent rain has been advantageous in the survival of mosquitoes that cause dengue fever. The rain brings water to pools, containers and encourages the growth of bushes and grasses which are breeding sites of mosquitoes. However, to a smaller extent rain also destroys habitants of mosquitoes and their breeding grounds, through floods which wash the eggs away (Gubler, Dengue & Monath, 200). Dengue fever is prevalent in both the tropics and subtropics. Outbreaks of the diseases have occurred recently in the Caribbean countries including Cuba, Puerto Rico and Central America. Cases of dengue fever have been imported by tourists returning from places with widespread incidence of dengue such as Singapore, South East Asia, South Pacific, India and West Indies. In the United States and a few other countries, dengue is the leading cause of acute febrile illness. Estimates from the centre for disease control show that there are at least a100 million cases of dengue fever and thousands of dengue hemorrhagic fever that require hospitalization during each year. The World Health Organization has estimated that about 22, 000 deaths occur each year as a result of dengue ever and these are more common among children (Johansen, 2002). Epidemiology of Dengue Fever Most of the victims of dengue fever can easily recover without any problems. The diseases has a mortality rate of less than one per cent where adequate treatment is given and less than 5% where adequate treatment is not given. Being one of the most common viral diseases transmitted by arthropods, dengue fever has a disease burden of more than 1500 disability-adjusted life years per one million human populations, making it similar to other topical and childhood diseases such as tuberculosis. Given tat dengue is largely a tropical disease, it is designated second is severity to malaria (Gubler, Dengue, Monath, 2001). Research studies for the persistence of the disease in Australia show that the incidence rate of dengue has increased by more than 30 times in the last three decades. The rapid increase in the incident rate is a combination of several factors which include rapid urbanization, high population growth, global warming and increased international travel. Geographically, dengue fever is more concentrated around the equator with about 1.7 people living in high endemic areas in Africa, Asia and the Pacific (Gu &Novak, 2005). In Australia, the rate of dengue infection among those who visit and return from endemic areas is about 5% and is the second most important infection to be diagnosed among this group after malaria. Like other arboviruses, the dengue virus is naturally maintained in cycles which involve the virus’s preferred blood-sucking vectors as well as vertebrate hosts (Gu & Novak, 2005). Primarily, the dengue viruses are preserved in forests in Africa and South East Asia through transmission from aedes mosquitoes to the offspring and to lower primates. The virus gets transmitted to human beings in rural areas by Aedes aegypti and certain other species of aedes which include aedes albopictus. In urban areas, the dengue virus is mainly transmitted to human beings by aedes aegypti. In all these cases, the infected human beings or lower primates increase the number of circulating dengue viruses through a process called amplification (Chow et al, 1998). The urban cycle of dengue virus is the most significant to infection of dengue virus in human beings and is strongly confined to cities and towns. In the last few decades, rapid urbanization in endemic areas as well as increased mobility of people has increased the number of circulating viruses and epidemics. As such, although dengue fever was at one time confined only to south East Asia, it has now spread to America and countries in south pacific and may be major threat to the people of Europe (Muir & Kay, 1994). Government Policies for Combating Spread Of Dengue Virus The high dengue fever morbidity rates and mortality cases in Australia are an issue of serious concern for the government (Johansen et al, 2002). Essentially, the spread of the dengue virus poses a major global problem. In addition, this important pubic health challenge is compounded by lack of adequate information on prevention strategies, which is turn is a major determining factor for the dengue epidemic. In Australia and in some other countries, dengue fever has a detrimental impact on accumulation of human capital and economic growth (Beckett et al, 2005). Further more the dengue fever virus has a high negative impact on venerable groups such as children. It is for this reason that the Australian government has taken initiatives to combat the spread of the deadly virus. In particular, the government has given more attention to prevention programs targeted at the most vulnerable groups. Interventions aimed at children have been very much effective in combating the spread of the virus. The government has spearheaded pooling of resources through partnerships as a way of expanding services (Gu & Novak, 2005). The government has also sought to improve response to dengue epidemics following heavy rainfalls. Dengue detection and warning systems have been put in place to facilitate routine collection and analysis of data for early detection of dengue epidemics. In order to utilize resources effectively in emergency situations, coordination of activities between relevant organizations and stakeholders has been enhanced. Selective use of anti-mosquito sprays for outdoor spraying has been a recommendable initiative for preventing the epidemics (Ritchie et al, 2004). This initiative has been carried out alongside other environmental initiatives such as improvement of homestead hygiene. Distribution of insecticide-treated nets continues to be an integral part of government policy in rolling back the spread of dengue virus. The benefits of this initiative have been enhanced by the government’s efforts in providing free bed nets to vulnerable groups (Gubler, Dengue & Monath, 2001). The Australian government’s efforts in combating dengue virus are in line and in collaboration with efforts by the international and regional community. One of the objectives of the Millennium Development Goals is to halt and reverse the spread of dengue virus by 2015 (Guzman, Ding, Xiao & Tesh, 2005). Various countries including Australia have endorsed a plan of action to roll back dengue fever. These plans have recognized that the dengue virus is not only a health issue but also a development challenge. As such, developments to move away from the wish list and establish time bound targets for spurring appropriate actions are noteworthy (Pankhong et al, 2002). It is possible to accelerate the progress already achieved. More dengue prevention targets have been achieved because the country’s political commitment, scientific knowledge and adequate resources have been directed at prevention and control initiatives. This has not only had an overall effect on improved well being for Australia’s population but also in increased economic growth and reduced poverty. In fact, 1.6% of annual economic growth in Australia between 1970 and 2000 has been attributed to massive improvement in public health (Gu & Novak, 2005). However, these initiatives have not been all that much satisfactory. Dengue fever still continues to take a substantial toll on health systems in Australia and contributes significantly to high morbidity rates in the country (Johansen et al, 2002). Research Studies on Dengue Fever Various research efforts have been made to prevent and treat dengue fever. Some of these efforts include development of vaccines and antiviral drugs as well as vector control. Regarding vector control, various methods have been used to inhibit the increase of mosquito numbers. Some of the most successful vector control includes placing guppy in stagnant waters to eat the larvae (Bangs et al, 2001). Numerous programs are being taken to develop a vaccine covering all the four serotypes of the virus. A major concern is that a vaccine may increase risks of disease severity through anti-body dependency enhancements. Currently, virus vaccines are undergoing testing and it is hoped that the first product will be available for commercial purposes in the next 2-3 years. If viable, the ideal vaccine should be safe ad effective after small number of injections. In addition, the vaccine should cover all the four serotypes besides being cost-effective and affordable (Beckett et al, 2005). In addition to attempts to contain the spread of mosquitoes and efforts to develop a vaccine for the dengue fever disease, efforts are underway to develop a range of antiviral drugs. These drugs will be helpful in treating dengue fever attacks and prevention of severe complications (Beckett et al, 2005). To this end, laboratory researches on the structure of viral proteins will be helpful in the development of the antiviral drugs. One of the approaches in this case is to inhibit the viral RNA-dependent RNA polymerase. This viral is responsible for copying the viral genetic material. Again, it can be possible to develop inhibitors of the viral protease which is responsible for the splicing of viral proteins. Additionally, it would be possible to produce entry inhibitors, which prevent the virus from entering the cells or inhibiting the capping process, which is essential for replication of viruses (Guzman, Ding, Xiao & Tesh, 2005). Primarily, treatment of dengue fever is symptomatic with adequate hydration and paracetamol to relief fever. Certain medicines such as ibuprofen and aspirin are not recommended because they aggravate bleeding. Patients with dengue hemorrhage fever should be hospitalized for monitoring and fluid therapy. It is advisable for mosquito avoidance measures to be taken to avoid transmission of the virus to mosquitoes (Chow et al, 1998). Prevention of Dengue Fever and Management Strategy Transmission of the dengue virus to mosquitoes must be interrupted to prevent the virus from spreading to other people (Bangs et al, 2001). For this reason, patients with dengue fever are kept under netting until the second bout of the dengue fever is over, at which time they are no longer contagious. Basically, prevention of dengue fever entails eradicating the mosquitoes which transmit the dengue virus. In countries plagued by the epidemic, people are usually urged to drain stagnant waters from trash cans, old tires and flower pots. A range of government initiatives to reduce mosquito prevalence can help keep the fever at check (Gubler, Dengue, Monath, 2001). To prevent mosquito bites, people are advised to wear long sleeved clothes and pants. For personal protection, people should use mosquito repellant spays when traveling to places where dengue fever is endemic. Usually, there are no specific risk factors for contracting dengue fever, except when one lives in or travels to places where mosquitoes and the fever are endemic. Limiting the level of exposure to mosquitoes by draining stagnant water and staying indoors a few hours after sunrise and before sunset can help decrease the severity of the virus (Pankhong et al, 2002). The strategy for investigating the virus at the primary care level is directed mainly at investigating the likelihood that a febrile illness can be a dengue infection (Muir & Kay, 1994). If the dengue is provisionally diagnosed, then the main purpose of the investigator is to determine the likelihood of developing complications and whether the patient may require hospitalization. As such, a system should be in place for facilitating blood investigation results to be reviewed early enough because any delays in acting on unusual results can have adverse consequence besides exacerbating the symptoms already experienced (Beckett et al, 2005). Stable and mild cases of dengue fever with good home environment as well as access to follow up should be monitored closely at home. In addition, patients should be advised to closely monitor gum bleeding, easy bruising, epistaxis, menorrhagia and hemetemesis. They should be advised and educated to go for emergency treatment if severe abdominal pains or symptoms of circulatory failure develop. It is important that patients are reviewed at least once in a day. Assessments during such reviews should take into consideration general conditions, hydration, presence of hemorrhagic phenomenon and circulatory sufficiency. Blood circulations should also be carried out and these should include platelet and hematotic count as well as total white blood cell count (Chow et al, 1998). Effect of Vaccination of Dengue Transmission Vaccinations prevent direct transmission of pathogens by preventing individual infections and indirectly by reducing likelihood of contact between susceptible individuals and infected ones. The potential effect of future dengue vaccines on transmission of the virus have only been estimated using a range of mathematical and statistical models of transmission (Bangs et al, 2001). However, there are considerable uncertainties on the structure of models that can be used to accurately describe the dynamics of dengue transmission. As such, it is impossible to tell the exact impact of dengue vaccines on its transmission. References Bangs, M., Tan, E., Listiyanigsih, B., Kay, H. and Porter, K. (2001). Detection of dengue viral RNA in Aedes aegypti (Diptera: Culicidae) exposed to sticky lures using reverse transcriptase polymerase chain reaction. J. Med. Entomol. 38(1), p. 720–724. Beckett, C. G., H. Kosasih, I. Faisal, Nurhayati, R. Tan, S. Widjaja, E. Listiyaningsih, C. Ma’roef, S. Wuryadi, M. and Bangs, J. (2005). Early detection of dengue infections using cluster sampling around index cases. Am. J. Trop. Med. Hyg. 72(2), p. 777–782. Chow, V. T K., Y. C. Chan, R. Yong, K. M. Lee, L. K. Lim, Y. K. Chung, S. G. Lam-Phua, and B. T. Tan. (1998). Monitoring of dengue viruses in field-caught Aedes aegypti and Aedes albopictus mosquitoes by a type-specific polymerase chain reaction and cycle sequencing. Am. J. Trop. Med. Hyg. 58(8), p. 578–586. Gu, W. and R. J. Novak. (2005). Short report: detection probability of arbovirus infection in mosquito populations. Am. J. Trop. Med. Hyg. 71(1), 636–638. Gubler, D. J. (2001). Dengue. Monath, T. P. (2001). The arboviruses: epidemiology and ecology. vol. 2(1), p. 223–260. CRC. Boca Raton, FL. Guzman, H., X. Ding, S-Y. Xiao, and R. B. Tesh. (2005). Duration of infectivity and RNA of Venezuelan equine encephalitis, West Nile, and yellow fever viruses dried on filter paper and maintained at room temperature. Am. J. Trop. Med. Hyg. 72(4), p. 474–477. Johansen, C. A., R. A. Hall, A. F. van den Hurk, S. A. Ritchie, and J. S. Mackenzie. (2002). Detection and stability of Japanese encephalitis virus RNA and virus viability in dead infected mosquitoes under different storage condition. Am. J. Trop. Med. Hyg. 67(2), p. 656–661. Muir, L. E. and B. H. Kay. (1994). Development of a disposable lure for Aedes aegypti, a vector of dengue. Arbovirus Res. Aust. 6(5), p. 37–39. Pankhong, P. et al. (2002). Molecular serotyping of dengue viruses in field-caught Aedes mosquitos by in-house RNA extraction/RT-PCR reagent kits. Southeast Asian J. Trop. Med. Public Health 33(3), p. 139–144. Ritchie, S. A., S. Long, G. Smith, A. Pyke, and T. B. Knox. (2004). Entomological investigations in a focus of dengue transmission in Cairns, Queensland, Australia, by using the sticky ovitrap. J. Med. Entomol. 41(1), p. 1–4. Read More

Minimum humidity is also a factor that has great impact on the spread of dengue fever disease. When there is relative humility, spread of the disease reduces. This is because newly laid eggs are destroyed making the survival of mosquito larvae minimal. The adults get wet and this reduces their lifetime making them not to affect many people. Hence humidity has a great impact on the survival of mosquitoes. To a greater extent rain has been advantageous in the survival of mosquitoes that cause dengue fever.

The rain brings water to pools, containers and encourages the growth of bushes and grasses which are breeding sites of mosquitoes. However, to a smaller extent rain also destroys habitants of mosquitoes and their breeding grounds, through floods which wash the eggs away (Gubler, Dengue & Monath, 200). Dengue fever is prevalent in both the tropics and subtropics. Outbreaks of the diseases have occurred recently in the Caribbean countries including Cuba, Puerto Rico and Central America. Cases of dengue fever have been imported by tourists returning from places with widespread incidence of dengue such as Singapore, South East Asia, South Pacific, India and West Indies.

In the United States and a few other countries, dengue is the leading cause of acute febrile illness. Estimates from the centre for disease control show that there are at least a100 million cases of dengue fever and thousands of dengue hemorrhagic fever that require hospitalization during each year. The World Health Organization has estimated that about 22, 000 deaths occur each year as a result of dengue ever and these are more common among children (Johansen, 2002). Epidemiology of Dengue Fever Most of the victims of dengue fever can easily recover without any problems.

The diseases has a mortality rate of less than one per cent where adequate treatment is given and less than 5% where adequate treatment is not given. Being one of the most common viral diseases transmitted by arthropods, dengue fever has a disease burden of more than 1500 disability-adjusted life years per one million human populations, making it similar to other topical and childhood diseases such as tuberculosis. Given tat dengue is largely a tropical disease, it is designated second is severity to malaria (Gubler, Dengue, Monath, 2001).

Research studies for the persistence of the disease in Australia show that the incidence rate of dengue has increased by more than 30 times in the last three decades. The rapid increase in the incident rate is a combination of several factors which include rapid urbanization, high population growth, global warming and increased international travel. Geographically, dengue fever is more concentrated around the equator with about 1.7 people living in high endemic areas in Africa, Asia and the Pacific (Gu &Novak, 2005).

In Australia, the rate of dengue infection among those who visit and return from endemic areas is about 5% and is the second most important infection to be diagnosed among this group after malaria. Like other arboviruses, the dengue virus is naturally maintained in cycles which involve the virus’s preferred blood-sucking vectors as well as vertebrate hosts (Gu & Novak, 2005). Primarily, the dengue viruses are preserved in forests in Africa and South East Asia through transmission from aedes mosquitoes to the offspring and to lower primates.

The virus gets transmitted to human beings in rural areas by Aedes aegypti and certain other species of aedes which include aedes albopictus. In urban areas, the dengue virus is mainly transmitted to human beings by aedes aegypti. In all these cases, the infected human beings or lower primates increase the number of circulating dengue viruses through a process called amplification (Chow et al, 1998). The urban cycle of dengue virus is the most significant to infection of dengue virus in human beings and is strongly confined to cities and towns.

In the last few decades, rapid urbanization in endemic areas as well as increased mobility of people has increased the number of circulating viruses and epidemics.

Read More