Containing an Epidemic: A Study of the Spread and Control of Rabies

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1 Freeman 1 Leah Freeman Dr. LeFebvre and Master Dockter COSMOS Cluster 7 July 30, 2012 Containing an Epidemic: A Study of the Spread and Control of Rabies Abstract: Rabies spread and control is an important aspect to the study of the virus because it is focused on its prevention. Epidemiology, the study of epidemics, is applied to rabies and can help form effective means of prevention. The molecular study and the observation of the overall trends of the virus can create the most useful preventative measures and provide the best plan of action in regards to rabies control. Although there are concerns about certain aspects of the prevention methods as well as some public and national indifference, researchers and scientists are working on a way to eliminate rabies. Rabies a word that has had negative connotations and bad feelings for generations. This terrible disease has plagued the world for thousands of years, yet is still present in today's society. Different countries, states, and territories have developed their own techniques of rabies prevention because of its effect on the populations of the world. Throughout history, they have understood that preventative means are necessary to combat the disease. In order to fully eliminate it from the mass of viruses in the world, a complete comprehension of its spread is necessary. This knowledge can help form a more firm control over the virus, as well as create more effective prevention methods. Through further research and study of the trends of the virus and the specific details of transmission tendencies, there is a promising possibility for the eventual eradication of the disease. Epidemiology, the study of the incidence and prevalence of disease in large populations and the detection of the sources and causes of epidemics, is important to the control of the rabies virus on both the molecular level and the worldwide level. A focus on the minute details of rabies study is crucial to the containment and prevention of rabies. Throughout the years,

2 Freeman 2 researchers have gathered information about the genetic variations among the different rabies viruses that should provide information helpful in the control of this disease by clearly identifying the species involved in maintaining particular rabies virus variants (Jackson and Wunner 114). As a result, the most effective approach in regards to the monetary aspects and overall usefulness can be applied to rabies control. (Jackson and Wunner 144). While the study of the individual viruses in an epidemic is extremely significant, a concentration on the overall impact of such viruses on the environment in its entirety is also important. Scientists have implemented mathematical modeling as a means of mapping the general trends of the rabies viruses. This method of observation "has become an important tool in analyzing the epidemiological characteristics of infectious diseases and can provide useful control measures" (Jin et al. par. 5). When combined, the findings from both areas of rabies epidemiology can offer more efficient and effective ways to control rabies and prevent it from spreading even further. Although rabies is becoming more and more of a problem amongst wild animals, domestic dogs still play a significant role in its spread. This is made clear through statistical evidence that states that "[a]pproximately 99% of all [human] rabies deaths occur in the developing world and throughout these regions the domestic dog is still the major reservoir host for virus variants associated with most deaths (Jackson and Wunner 133). The major explanation for this is that in underdeveloped countries, vaccines are not as available and other preventative measures are not taken. In fact, this lack of prevention is the only reason dog bites are the leading cause of human rabies deaths. In developed areas, where canine rabies has been brought under control through vaccinations, almost all of the human rabies cases are the result of a bite from a wild animal ( Rabies: Disease Transmission, Progression, and Control par. 3). Therefore, if prevention methods were more effectively implemented in developing countries,

3 Freeman 3 the number of human rabies deaths worldwide would theoretically decrease. While these methods are well developed and effective where they have been deployed appropriately, they must be more effectually applied in order to achieve their maximum potential (Jackson and Wunner 589). Prevention on a large scale is increasingly important to the control of rabies. While some treatments for rabies exist, prevention is key to eradicating the disease. Possible methods of prevention include decreasing the dog birth rate, mandatory immunization and registration of domestic dogs, a reduction in the price of vaccines, an enhancement of awareness of prevention, contraceptive measures, and the fostering and adoption of stray dogs (Jin et al. par 23). While these tactics are more focused on domestic animals, the rabies problem in wild animals still continues unchecked. An increasingly popular approach to rabies control amongst wild animals is a mass-distributed vaccine called the Oral Rabies Vaccination (ORV). This method involves the insertion of a vaccine into some form of bait that is left in the wild for animals to each and become subsequently vaccinated. The ORV has shown great promise, as evidenced by Switzerland, which had a long enzootic [afflicting animals in a particular area] for rabies in red foxes and was the first country to use ORV in wildlife in 1978, [being] declared free of rabies [in 1999] (Childs, Hanlon, and Nettles 3). However, not everyone understands the importance of rabies prevention. In certain cases, animal owners do not take the necessary preventative measures for their own pets, thereby increasing the risk of rabies. Increased public awareness of the dangers of such neglect of prevention could possibly help lead to fewer rabies cases and therefore fewer deaths. In addition to the marked lack of awareness, [a]t the national level, there is a lack of motivation, commitment and particularly, resources, to gather data to promote a rabies control agenda, which is not encouraging for the ultimate elimination of rabies (Jackson

4 Freeman 4 and Wunner 589). There is an evident need for improved prevention because studies show that "if no further effective prevention and control measures are taken, the disease will not vanish" (Jin et al. par. 15). The spread of rabies occurs in two types of transmission, iatrogenic and non-iatrogenic. Iatrogenic refers to the human-to-human transfer caused by a physician's actions. However, this type of transmission is very rare, although well-documented, and occurs mainly through corneal and organ transplantations from undiagnosed patients (Jackson and Wunner 143). More commonly, the virus spreads in a non-iatrogenic way and is transferred by natural means, almost always in the form of a bite. The infected saliva is inserted into the bitten animal or human, subsequently transferring the virus into the new host. Other natural forms of transmission, such as the contamination of mucous membranes (i.e., eyes, nose, mouth), [and] aerosol transmission ( Rabies: How is Rabies Transmitted par. 2), are possible; however, these manners of transfer are uncommon and only account for a very small percentage of rabies deaths in humans. Rabies is transferred through reservoir hosts animals that maintain the rabies virus in nature and then pass on the virus to other animals (Bruce and Wild 1). Common hosts include dogs, foxes, skunks, raccoons, coyotes, and bats. ( Rabies: Disease Transmission, Progression, and Control par. 3). In general, each species of host has its own unique strain of the rabies virus. However, the different rabies viruses are not confined to a certain species as its reservoir host. Spillover, the transfer of a certain virus variant to a new host, can occur. According to studies that have been conducted, [i]t is becoming clear that adaptation of rabies viruses to new hosts is a phenomenon that is far more frequent than originally supposed as evidenced by the emergence of sylvatic [originating from the woods] rabies from dog reservoirs and the emergence of rabies

5 Freeman 5 in terrestrial [land] hosts after spillover from chiropteran [bat] reservoirs. (Jackson and Wunner 114). This is troubling because if one type of rabies virus, such as one transmitted primarily by dogs, was eliminated, dogs could once again become carriers of a different rabies virus that originated in bats. Therefore, in order to completely eradicate rabies, a concentrated focus on the forced extinction of the disease among bats would yield the most promising results. This can only be possible through a better understanding of the evolutionary forces acting on these viruses during the adaptive process to a new host and further molecular epidemiological investigations (Jackson and Wunner 115). Rabies has a prominent impact on the environment, and because of this concerns have arisen about methods of control and the benefits and consequences of such measures. With innovative and novel ideas for any new type of preventative measure, there are advocates and opponents. In regards to rabies, what seems to be the most common argument against prevention methods is the monetary cost. While rabies control is a compelling subject for improvement, not everyone is willing to allow the necessary funds to be accessed. Yet, as with any widespread disease control program, expenses are required, and through studies, researchers are able to design methods that will be the most cost-effective. Another possible problem that some are concerned about is an overreaction to rabies by the public. Since rabies is widely accepted as a frightening and unwanted disease, some would go to great lengths to ensure that rabies would not spread any farther. There is always the "potential for malicious and indiscriminate killing of large colonies of bats" and other animals that commonly carry the virus (Federal Aid in Wildlife Restoration 3). Scientists and researchers are not too keen on a complete wipe-out of an entire species in a certain area simply because of the chance that one of the animals has rabies and therefore the potential of infecting a human. This idea has already been rejected, and if the public

6 Freeman 6 people took it upon themselves to take the rabies problem into their own hands, it would not only endanger the wildlife, but also waste money and resources. Rabies is a growing problem in the modern world. The virus is becoming more and more prevalent among human interactions with wildlife. In the United States, the percentage of rabies deaths after a bite from a wild animal has surpassed that of a dog bite. However, canine rabies is also still a problem in the developing world. Improved prevention is necessary for the elimination of dog rabies in those areas, as well as for rabies spread by wildlife populations. The worldwide impact of rabies deserves the attention of scientists, researchers, and support, and without it, there will be no change for the better. Yet despite certain obstacles, such as spillover of different virus variants and an apparent social apathy, with continued study of the nature of the disease and its transmission as well as the overall trends of infection, preventative methods and a better control over rabies can be achieved.

7 Freeman 7 Works Cited Childs, James E., Cathleen A. Hanlon, and Victor F. Nettles. Rabies in Wildlife PDF file. Connery, Bruce, and Dr. Margaret A. Wild. Rabies and Rabies Control in Wildlife: Application to National Park System Areas PDF file. Federal Aid in Wildlife Restoration. Controlling the Spread of Rabies in Wildlife and Transmission to Humans PDF file. Jackson, Alan C., and William H. Wunner. Rabies. 2nd ed. Great Britain: Elsevier/Academic Press, Print. Jin, Zhen, Shigui Ruan, Gui-Quan Sun, Juan Zhang, and Tao Zhou. Analysis of Rabies in China: Transmission Dynamics and Control. PLoS ONE July Rabies: Disease Transmission, Progression, and Control Haverford University. Rabies: How is Rabies Transmitted? Center for Disease Control and Prevention July July 2012.