RABIES
Rabies ( From Latin: rabies, "madness, rage, fury." Also known as "hydrophobia") is a viral zoonotic neuroinvasive disease that causes acute encephalitis (inflammation of the brain) in mammals. It is most commonly caused by a bite from an infected animal, as the virus is present in the saliva of the infected creature. If left untreated it is almost invariably fatal.
Vectors
Any mammal may become infected with the rabies virus and develop symptoms. Most animals can transmit the disease to humans. Infected bats, monkeys, raccoons, foxes, skunks, cattle, wolves, dogs or cats provide the greatest risk to humans. Rabies may also spread through exposure to infected domestic farm animals, groundhogs, weasels and other wild carnivores. Rodents are seldom infected.
The virus is usually present in the nerves and saliva of a symptomatic rabid animal. The route of infection is usually, but not necessarily, by a bite (In many cases the infected animal is exceptionally aggressive, may attack without provocation, and exhibits otherwise uncharacteristic behaviour ) . Transmission may also occur via an aerosol through mucous membranes.
Transmission between humans is extremely rare, but it can happen through transplant surgery, or bites, kisses or sexual relations.
After a typical human infection by bite, the virus enters the peripheral nervous system. It then travels along the nerves towards the central nervous system to the brain. The incubation period of the disease depends on how far the virus must travel to reach the central nervous system, usually taking a few months. During this phase, the virus cannot be easily detected but vaccination may still confer cell-mediated immunity to prevent symptomatic rabies. Once the infection reaches the central nervous system and symptoms begin to show, the untreated infection is fatal within days. Once the virus reaches the brain, it rapidly causes encephalitis. At this time, treatment is useless.
Rabies and animals
Three stages of rabies are recognized in dogs and other animals. The first stage is a one to three day period characterized by behavioral changes and is known as the prodromal stage. The second stage is the excitative stage, which last three to four days. It is this stage that is often known as furious rabies due to tendency of the affected dog to be hyperreactive to external stimuli and bite at anything near. The third stage is the paralytic stage and is caused by, damage to motor neurons. Incoordination is seen due to rear limb paralysis and drooling and difficulty swallowing is caused by paralysis of facial and throat muscles. Death is usually caused by respiratory arrest
Symptoms
In humans. The period between infection and the first flu-like symptoms is normally two to twelve weeks, but can be as long as two years.
In the beginning stages of rabies, the symptoms are malaise, headache, and fever. In later stages it includes acute pain, violent movements, uncontrolled excitements, depressions, partial paralysis, cerebral dysfunction, anxiety, insomnia, confusion, agitation, abnormal behavior, paranoia, terror, hallucinations, progressing to delirium. The production of large quantities of saliva and tears coupled with an inability to speak or swallow are typical during the later stages-of the disease; this can result in "hydrophobia", where the victim has difficulty swallowing because the throat and jaw become slowly paralyzed, shows panic when presented with liquids to drink.
In the final stages the patient begins to have periods of mania, lethargy and coma.
Death almost invariably results two to ten days after the first symptoms and it's genęrally cause by respiratory failure. The few humans who are known to have survived the disease were all left with severe brain damage
Diagnosis
The reference method for diagnosing rabies is by performing PCR or viral culture on brain samples taken after death. The diagnosis can also be reliably made from skin samples taken before death. It is also possible to make the diagnosis from saliva, urine and cerebrospinal fluid samples'.
Treatment
Treatment after exposure, known as post-exposure prophylaxis or "P.E.P." is highly successful in preventing the disease if administered promptly, generally within six days of infection. Thoroughly washing the wound as soon as possible with soap and water for approximately five minutes is very effective at reducing the number of viral particles. In the United States, patients receive one dose of immunoglobulin and five doses of rabies vaccine over a twenty-eight day period. The first dose of rabies vaccine is given as soon as possible after exposure, with additional doses on days three, seven, fourteen, and twenty-eight after the first.
Rabies is treatable while the virus is present in tissues composed of cells other than neurons, such as skin and muscle. However, once the infection spreads to a neuron, the virus is sequestered from the immune system and will eventually make its way to the spinal cord and then to the brain. Treatment at this point is futile, even though symptoms may begin to appear weeks or even months later.
Prevention
Immunization - immunize against the disease.
Rabies can be prevented by vaccination, both in humans and other animals. In many jurisdictions, domestic dogs, cats, are required to be vaccinated. A pre-exposure vaccination is also available for humans, most commonly given to veterinarians and those traveling to regions where the disease is common, such as India.