Rabies

Rabies (. From rabies) is a viral neuroinvasive disease that causes acute encephalitis (inflammation of the brain) in warm-blooded animals. It is zoonotic (i.e., transmitted by animals), most commonly by a bite from an infected animal but occasionally by other forms of contact. Rabies is almost invariably fatal if post-exposure prophylaxis is not administered prior to the onset of severe symptoms. It is a significant killer of livestock in some countries.

The rabies virus travels to the brain by following the peripheral nerves. 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. Once the infection reaches the central nervous system and symptoms begin to show, the infection is practically untreatable and usually fatal within days.

Early-stage symptoms of rabies are malaise, headache and fever, later progressing to more serious ones, including acute pain, violent movements, uncontrolled excitement, depression and inability to swallow water. Finally, the patient may experience periods of mania and lethargy, followed by coma. The primary cause of death is usually respiratory insufficiency. 97% of human rabies cases come from dog bites.

Etymology
The term is derived from the Latin rabies, "madness". This, in turn, may be related to the Sanskrit rabhas, "to do violence". The Greeks derived the word "lyssa", from "lud" or "violent"; this root is used in the name of the genus of rabies lyssavirus.

Virology
The rabies virus is the type species of the Lyssavirus genus, which encompasses other similar viruses. Lyssaviruses have helical symmetry, with a length of about 180 nm and a cross-sectional diameter of about 75 nm. These viruses are enveloped and have a single stranded RNA genome with negative-sense. The genetic information is packaged as a ribonucleoprotein complex in which RNA is tightly bound by the viral nucleoprotein. The RNA genome of the virus encodes five genes whose order is highly conserved. These genes are nucleoprotein (N), phosphoprotein (P), matrix protein (M), glycoprotein (G) and the viral RNA polymerase (L).

From the point of entry, the virus travels quickly along the neural pathways into the central nervous system (CNS), and then further into other organs. The salivary glands receive high concentrations of the virus thus allowing further transmission.

Symptoms
The period between infection and the first flu-like symptoms is normally two to twelve weeks, but can be as long as two years. Soon after, the symptoms expand to slight or 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”, in which the patient has difficulty swallowing because the throat and jaw become slowly paralyzed, shows panic when presented with liquids to drink, and cannot quench his or her thirst. The disease itself was also once commonly known as hydrophobia (or aquaphobia), from this characteristic symptom.

Death almost invariably results two to ten days after the first symptoms; the few humans who are known to have survived the disease were all left with severe brain damage, with one recorded exception purportedly resulting from implementation of the Milwaukee protocol. It is neurotropic in nature.

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, but this is not as sensitive. Inclusion bodies called Negri bodies are 100% diagnostic for rabies infection, but found only in 20% of cases.

The differential diagnosis in a case of suspected human rabies may initially include any cause of encephalitis, particularly infection with viruses such as herpesviruses, enteroviruses, and arboviruses (e.g., West Nile virus). The most important viruses to rule out are herpes simplex virus type 1, varicella-zoster virus, and (less commonly) enteroviruses, including coxsackieviruses, echoviruses, polioviruses, and human enteroviruses 68 to 71. In addition, consideration should be given to the local epidemiology of encephalitis caused by arboviruses belonging to several taxonomic groups, including eastern and western equine encephalitis viruses, St. Louis encephalitis virus, Powassan virus, the California encephalitis virus serogroup, and La Crosse virus.

New causes of viral encephalitis are also possible, as was evidenced by the recent outbreak in Malaysia of some 300 cases of encephalitis (mortality rate, 40%) caused by Nipah virus, a newly recognized paramyxovirus. Similarly, well-known viruses may be introduced into new locations, as is illustrated by the recent outbreak of encephalitis due to West Nile virus in the eastern United States. Epidemiologic factors (e.g., season, geographic location, and the patient’s age, travel history, and possible exposure to animal bites, rodents, and ticks) may help direct the diagnostic workup.

Cheaper rabies diagnosis will be possible for low-income settings according to research reported on the Science Development Network website in 2008. Accurate rabies diagnosis can be done at a tenth of the cost, according to researchers from the Farcha Veterinary and Livestock Research Laboratory and the Support International Health Centre in N'Djamena, Chad. The scientists evaluated a method using light microscopy, cheaper than the standard tests, and say this could provide better rabies control across Africa.

Prevention
Every infected case with rabies resulted in death until a vaccine was developed by Louis Pasteur and Émile Roux in 1885. Their original vaccine was harvested from infected rabbits, from which the nerve tissue was weakened by allowing it to dry for five to ten days. Similar nerve tissue-derived vaccines are still used in some countries, as they are much cheaper than modern cell culture vaccines. The human diploid cell rabies vaccine (H.D.C.V.) was started in 1967; however, a new and less expensive purified chicken embryo cell vaccine and purified vero cell rabies vaccine are now available. A recombinant vaccine called V-RG has been successfully used in the field in Belgium, France, Germany and the United States to prevent outbreaks of rabies in wildlife. Currently pre-exposure immunization has been used in both human and non-human populations, whereas in many jurisdictions domesticated animals are required to be vaccinated.

In the U.S., since the widespread vaccination of domestic dogs and cats and the development of effective human vaccines and immunoglobulin treatments, the number of recorded deaths from rabies has dropped from one hundred or more annually in the early twentieth century, to 1–2 per year, mostly caused by bat bites, which may go unnoticed by the victim and hence untreated.

Post-exposure prophylaxis
Treatment after exposure, known as post-exposure prophylaxis or “P.E.P.”, is highly successful in preventing the disease if administered promptly, generally within ten 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. “If available, a virucidal antiseptic such as povidone-iodine, iodine tincture, aqueous iodine solution or alcohol (ethanol) should be applied after washing...Exposed mucous membranes such as eyes, nose or mouth should be flushed well with water.” In the United States, patients receive one dose of human rabies immunoglobulin (HRIG) and four doses of rabies vaccine over a fourteen day period. The immunoglobulin dose should not exceed 20 units per kilogram body weight. HRIG is very expensive and constitutes the vast majority of the cost of post-exposure treatment, ranging as high as several thousand dollars. As much as possible of this dose should be infiltrated around the bites, with the remainder being given by deep intramuscular injection at a site distant from the vaccination site. The first dose of rabies vaccine is given as soon as possible after exposure, with additional doses on days three, seven and fourteen after the first. Patients that have previously received pre-exposure vaccination do not receive the immunoglobulin, only the post-exposure vaccinations on day 0 and 3.

Modern cell-based vaccines are similar to flu shots in terms of pain and side effects. The old nerve-tissue-based vaccinations require multiple painful injections into the abdomen with a large needle, are cheap, and are now used only in remote poor areas in India, but are being phased out and replaced by affordable WHO ID (intradermal) vaccination regimens.

Intramuscular vaccination should be given into the deltoid, not gluteal area which has been associated with vaccination failure due to injection into fat rather than muscle. In infants the lateral thigh is used as for routine childhood vaccinations.

Finding a bat in the room of a sleeping infant is regarded as an indication for post-exposure prophylaxis. The recommendation for the precautionary use of post-exposure prophylaxis in occult bat encounters where there is no recognized contact has been questioned in the medical literature based on a cost-benefit analysis. However, recent studies have further confirmed the wisdom of maintaining the current protocol of precautionary administering of P.E.P. in cases where a child or mentally compromised individual has been left alone with a bat, especially in sleep areas (where a bite/or exposure may occur while the victim is asleep and unaware or awake and unaware that a bite occurred). This is illustrated by the case of a nine-year old boy from Quebec who died an agonizing death (over a 14 day period) from rabies 4 weeks after being in the presence of a sick bat, even though there was no apparent report of a bite; as shown in the following conclusion made by the doctors involved in the case: Despite recent criticism (45), the dramatic circumstances surrounding our patient's history, as well as increasingly frequent reports of human rabies contracted in North America, support the current Canadian guidelines which state that RPEP [P.E.P] is appropriate in cases where a significant contact with a bat cannot be excluded (46). The notion that a bite or an overt break in the skin needs to be seen or felt for rabies to be transmitted by a bat is a myth in many cases.

It is highly recommended that P.E.P. be administered as soon as possible. Begun without delay, or with very little delay, P.E.P. is 100% effective against rabies. In the case in which there has been a significant delay in administering P.E.P., the treatment should be administered regardless of that delay, as it may still be effective if it is not too late. If there has been a delay between exposure and attempts at treatment, such that the possibility exists that the virus has already penetrated the nervous system, the possibility exists that amputation of the affected limb might thwart rabies, if the bite or exposure was on an arm or leg. This treatment should be combined with an intensive PEP regimen.

Blood-brain barrier
Some recent works have shown that during lethal rabies infection, the blood-brain barrier (BBB) does not allow anti-viral immune cells to enter the brain, the primary site of rabies virus replication. This aspect contributes to the pathogenicity of the virus and artificially increasing BBB permeability promotes viral clearance. Opening the BBB during rabies infection has been suggested as a possible novel approach to treat the disease, even though no attempts have yet been made to determine whether or not this treatment could be successful.

Induced coma
In 2005, American teenager Jeanna Giese survived an infection of rabies unvaccinated. She was placed into an induced coma upon onset of symptoms and given ketamine, midazolam, ribavirin, and amantadine. Her doctors administered treatment based on the hypothesis that detrimental effects of rabies were caused by temporary dysfunctions in the brain and could be avoided by inducing a temporary partial halt in brain function that would protect the brain from damage while giving the immune system time to defeat the virus. After thirty-one days of isolation and seventy-six days of hospitalization, Giese was released from the hospital.

Giese's treatment regimen became known as the "Milwaukee protocol". To date only one other patient has survived under the protocol, despite numerous attempts at the treatment. Rodney Willoughby Jr., Giese's primary care physician, has asserted that subsequent failures occurred because patients were not given the same combination of drugs used in the initial incident.

On April 10th, 2008 in Cali, Colombia, an eleven year-old boy was reported to survive rabies and the induced coma without noticeable brain damage.

Ketamine
The anesthetic drug ketamine has shown the potential for rabies virus inhibition in rats.

Prognosis
In unvaccinated humans, rabies is almost always fatal after neurological symptoms have developed, but prompt post-exposure vaccination may prevent the virus from progressing. Rabies kills around 55,000 people a year, mostly in Asia and Africa. There are only six known cases of a person surviving symptomatic rabies, and only three known cases of survival in which the patient received no rabies-specific treatment either before or after illness onset.

Financial Consequences of Not Pre-vaccinating
"In Thailand, rabies remains a neglected disease with authorities continuing to rely on human death statistics while ignoring the financial burden resulting from an enormous increase in post-exposure prophylaxis. "

Past attempts to conduct a mass dog vaccination and sterilization program have been limited to Bangkok city and have not been successful. In Thailand, 20 rabies deaths were reported in 2003, compared to 200 a decade before as stepped up post exposure prophylaxis (PEP) immunoglobulin have reduced deaths. However, the financial burden of rabies has skyrocketed as 400,000 people received PEP, versus 90,000 in 1991. (PEP is more than 10 times more expensive to administer than pre-exposure (PREP) for those who haven't had PREP, and the cost is more than half the per capita annual income of the average citizen). The percentage of rabies infectivity of samples sent to diagnostic laboratories all over the country remains high, within the range of 30–40%. In China, this is the case as well as governments pour resources into PEP rather than vaccination programs.

Transmission


Any warm-blooded animal, including humans, may become infected with the rabies virus and develop symptoms. Indeed, the virus has even been adapted to grow in cells of poikilothermic vertebrates though natural transmission has only been documented among mammals. Most animals can be infected by the virus and can transmit the disease to humans. Infected bats, monkeys, raccoons, foxes, skunks, cattle, wolves, coyotes, dogs, mongoose (normally yellow mongoose) or cats present the greatest risk to humans. Rabies may also spread through exposure to infected domestic farm animals, groundhogs, weasels, bears and other wild carnivores. Rodents (mice, squirrels etc) 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 behavior.

Transmission between humans is extremely rare. A few cases have been recorded through transplant surgery.

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. During this phase, the virus cannot be easily detected within the host, and vaccination may still confer cell-mediated immunity to prevent symptomatic rabies. When the virus reaches the brain, it rapidly causes encephalitis. This is called the prodromal phase, and is the beginning of the symptoms. Once the patient becomes symptomatic, treatment is almost never effective and mortality is near 100%. Rabies may also inflame the spinal cord producing transverse myelitis.

Prevalence


The rabies virus survives in widespread, varied, rural fauna reservoirs. However, in Asia, parts of the Americas and large parts of Africa, dogs remain the principal host. Mandatory vaccination of animals is less effective in rural areas. Especially in developing countries, pets may not be privately kept and their destruction may be unacceptable. Oral vaccines can be safely distributed in baits, and this has successfully reduced rabies in rural areas of France, Ontario, Texas, Florida and elsewhere, like the City of Montréal, Québec, where baits are successfully used on raccoons in the Mont-Royal park area. Vaccination campaigns may be expensive, and a cost-benefit analysis can lead those responsible to opt for policies of containment rather than elimination of the disease.

There are an estimated 55,000 human deaths annually from rabies worldwide, with about 31,000 in Asia, and 24,000 in Africa. One of the sources of recent flourishing of rabies in East Asia is the pet boom. China introduced in the city of Beijing the “one-dog policy” in November 2006 to control the problem. India has been reported as having the highest rate of human rabies in the world, primarily because of stray dogs. As of 2007, Vietnam had the second-highest rate, followed by Thailand; in these countries too the virus is primarily transmitted through canines (feral dogs and other wild canine species). Recent reports suggest that wild rabid dogs are roaming the streets. Because much cheaper pre-vaccination is not commonly administered in places like Thailand, the expense for lack of preparation with far more costly post-exposure prophylaxis can hit families hard.

Rabies was once rare in the United States outside the Southern states, but as of 2006, raccoons in the mid-Atlantic and northeast United States had been suffering from a rabies epidemic since the 1970s, which was moving westwards into Ohio. In the midwestern United States, skunks are the primary carriers of rabies, comprising 134 of the 237 documented non-human cases.

Cultural impact
Because of its potentially violent nature, rabies has been known since 3500 B.C. The first written record of rabies is in the Codex of Eshnunna (ca. 1930 BC), which dictates that the owner of a dog showing symptoms of rabies should take preventive measure against bites. If a person was bitten by a rabid dog and later died, the owner was fined heavily.

Rabies was considered a scourge for its prevalence in the 19th century. Fear of rabies related to methods of transmissions was almost irrational; however, this gave Louis Pasteur ample opportunity to test post-exposure treatments in 1895.

Cultural references

 * Cujo, a Stephen King novel and film about a mother and son being terrorized by a rabid dog.
 * I Drink Your Blood, a 1970s cult horror film about a gang of Satanic hippies who get infected with rabies.
 * Old Yeller, a novel and film that involves a frontier dog becoming infected by a rabid wild wolf.
 * The Mad Death, a 1983 BBC TV series in which Britain is gripped by an outbreak of rabies after an afflicted pet cat is illegally smuggled into the country.
 * Rant, a novel by Chuck Palahniuk in which the main character infects those around him with rabies.
 * Rabies, a novel by Borislav Pekic about a genetically engineered Rabies virus with a double protein envelope, thus becoming extremely easy to transmit (biting is not neccessary any more), which spreads from one victim to another extremely fast. The virus gets turned loose at the London's Heathrow Airport.

Rabies in animals
Rabies is infectious to mammals. 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 lasts three to four days. It is this stage that is often known as furious rabies for the 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 owing 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.

As recently as 2004, a new symptom of rabies has been observed in foxes. Probably at the beginning of the prodromal stage, foxes, who are extremely cautious by nature, seem to lose this instinct. Foxes will come into settlements, approach people, and generally behave as if tame. How long such "euphoria" lasts is not known. But even in this state such animals are extremely dangerous, as their saliva and excretions still contain the virus and they remain very unpredictable.