Pink Eye (Conjunctivitis): Causes, Symptoms, and Treatments
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Rabies is a lethal zoonotic disease, meaning it can be transmitted from animals to humans. This disease is caused by a virus and is often fatal once the symptoms appear. It affects nearly all warm-blooded vertebrates, with animals possessing a well-developed dental system, such as dogs and foxes, being at a higher risk due to disease transmission primarily through bites.
The causative agent of rabies is an RNA virus, part of the Mononegavirales order. It belongs to the Rhabdoviridae family and the Lyssavirus genus, which encompasses seven genotypes and four serotypes. The most prevalent serotype in certain regions is type 1, affecting both domestic and wild carnivores.
The rabies virus has limited resistance outside its host. It is sensitive to various solvents, lipid detergents, and sunlight. Several disinfectants, including quaternary ammonium salts, 7% iodophors, and 1% soaps, can inactivate the virus. These products can also be applied directly to wounds as first aid after a bite from a potentially infected animal.
The primary mode of transmission for the rabies virus is through the bite of an infected animal, as the virus resides in the salivary glands and is thus expelled with saliva. However, other less common transmission methods exist, such as contagion via aerosols in closed environments with a high virus concentration, or through the oral route, requiring microlesions in the mouth as the virus is inactivated by the acidic pH of the stomach.
Rabies is a global disease, absent at the poles and in certain regions. It has the potential to affect all warm-blooded animals, including mammals and birds. Depending on the animal species involved, two different epidemiological cycles of rabies spread are identified: the urban and sylvan cycles.
The urban cycle involves domestic animals, with dogs being the primary source of virus preservation and transmission. The sylvan cycle involves different animal species depending on the geographical area. In some regions, the fox plays a significant role in maintaining the sylvan rabies cycle active due to its large movements and its ability to transmit the virus before symptoms appear, given the disease's long incubation period.
Rabies is most commonly transmitted through the bite of an infected animal, during which the virus is transferred to the healthy animal through saliva. The virus typically enters the body at the bite site, often a limb or an area with rich muscle tissue, where it initially replicates.
The rabies virus then mechanically migrates to reach the spinal cord through the nerves that innervate the affected muscle. Following further replication, the virus progresses to the brain in a process known as centripetal migration. Subsequently, there is a centrifugal migration, during which the virus localizes in the brain and reaches the salivary glands through the nerves, undergoing extensive replication.
However, it's important to note that during this stage, the infected animal is not capable of eliminating the rabies virus with its saliva, even if it remains asymptomatic. Ultimately, the virus spreads throughout the central nervous system, resulting in paralytic phenomena and leading to death, often caused by respiratory paralysis and asphyxia.
In summary, rabies is a deadly disease that poses a significant threat to both animals and humans. Understanding the virus, its transmission, and the progression of the disease is crucial for prevention and control. Vaccination and immediate treatment after potential exposure remain the most effective ways to prevent the disease.