Transmission Of Rabies From Animals To Humans example essay topic

Rabies is a preventable viral disease of mammals most often transmitted through the bite of a rabid animal. The vast majority of rabies cases reported to the Centers for Disease Control and Prevention (CDC) each year occur in wild animals like raccoons, skunks, bats, and foxes. Domestic animals account for less than 10% of the reported rabies cases, with cats, cattle, and dogs most often reported rabid. Rabies virus infects the central nervous system, causing encephalopathy and ultimately death. Early symptoms of rabies in humans are nonspecific, consisting of fever, headache, and general malaise.

As the disease progresses, neurological symptoms appear and may include insomnia, anxiety, confusion, slight or partial paralysis, excitation, hallucinations, agitation, hyper salivation, difficulty swallowing, and hydrophobia (fear of water). Death usually occurs within days of the onset of symptoms. over the last 100 years, rabies in the United States has changed dramatically. More than 90% of all animal cases reported annually to CDC now occur in wildlife; before 1960 the majority were in domestic animals. The principal rabies hosts today are wild carnivores and bats...

The number of rabies-related human deaths in the United States has declined from more than 100 annually at the turn of the century to one or two per year in the 1990's. Modern day prophylaxis has proven nearly 100% successful. In the United States, human fatalities associated with rabies occur in people who fail to seek medical assistance, usually because they were unaware of their exposure. Although human rabies deaths are rare, the estimated public health costs associated with disease detection, prevention, and control have risen, exceeding $300 million annually. These costs include the vaccination of companion animals, animal control programs, maintenance of rabies laboratories, and medical costs, such as those incurred for rabies post exposure prophylaxis (PEP). Accurate estimates of these expenditures are not available.

Although the number of PEPs given in the United States each year is unknown, it is estimated to be about 40,000. When rabies becomes epizootic or enzootic in a region, the number of PEPs in that area increases. Although the cost varies, a course of rabies immune globulin and five doses of vaccine given over a 4-week period typically exceeds $1,000. The cost per human life saved from rabies ranges from approximately $10,000 to $100 million, depending on the nature of the exposure and the probability of rabies in a region. Customarily, the level of international resources committed to the control of an infectious disease is a response to the associated human morbidity and mortality. For most infectious diseases, these data adequately reflect the deserved public health attention.

It is difficult, however, to estimate the global impact of rabies by using only human mortality data. Because vaccines to prevent human rabies have been available for more than 100 years, most deaths from rabies occur in countries with inadequate public health resources and limited access to preventive treatment. These countries also have few diagnostic facilities and almost no rabies surveillance. Under reporting is a characteristic of almost every infectious disease in developing countries, and increasing the estimated human mortality does not in itself increase the relative public health importance of rabies.

There is, however, one often neglected aspect of rabies that does affect perception of its importance. Rabies is not, in the natural sense, a disease of humans. Human infection is incidental to the reservoir of disease in wild and domestic animals; therefore, a more accurate projection of the impact of rabies on public health should include an estimate of the extent to which the animal population is affected and the expense involved in preventing transmission of rabies from animals to humans. An additional figure is needed to complete the global picture of rabies.

The best estimates of the impact of rabies on a country and the public health resources available within that country for rabies control are found in data for the number and distribution of cases of rabies in domestic animals. Despite evidence that control of dog rabies through programs of animal vaccination and elimination of stray dogs can reduce the incidence of human rabies, exposure to rabid dogs is still the cause of over 90% of human exposures to rabies and of over 99% of human deaths worldwide. The cost of these programs prohibits their full implementation in much of the developing world, and in even the most prosperous countries the cost of an effective dog rabies control program is a drain on public health resources. The estimated annual expenditure for rabies prevention in the United States is over US$300 million, most of which is spent on dog vaccinations.

An annual turnover of approximately 25% in the dog population necessitates re vaccination of millions of animals each year, and re introduction of rabies through transport of infected animals from outside a controlled area is always a possibility should control programs lapse. Reservoirs of wildlife rabies, virtually unknown in Asia and tropical regions, are also potential sources of rabies infection for dogs in Europe and North America. Rabies virus belongs to the order Mononegavirales, viruses with a non segmented, negative-stranded RNA genome. Within this group, viruses with a distinct 'bullet's have are classified in the Rhabdoviridae family, which includes at least three genera of animal viruses, Lyssavirus, Ephemerovirus, and Vesiculovirus. The genus Lyssavirus includes rabies virus, Lagos bat, Mo kola virus, Duvenhage virus, European bat virus 1 & 2 and a newly discovered Australian bat virus. StructureRhabdoviruses are approximately 180 nm long and 75 nm wide.

The rabies genome encodes five proteins: nucleoprotein (N), phosphoprotein (P), matrix protein (M), glycoprotein (G) and polymerase (L). All are have two major structural components: a helical core (RNP) and a surrounding envelope. In the RNP, the genome RNA is tightly encased by the nucleoprotein. Two other viral proteins, the phosphoprotein and the large protein (or polymerase) are associated with the RNP. The glycoprotein forms approximately 400 trim eric spikes which are tightly arranged on the surface of the virus. The M protein is associated both with the envelope and the RNP and may be the central protein of assembly. web Dakota Department of Health Division of Microbiology 1205 Ave A West Bismarck, ND 58506 web article / internal reference / rabies web Virology / Special/Rabies 1/Rabies. htm web.