All About Rabies
Ron Hines DVM PhD
Read a federally-funded study on rabies here
The problem with one vaccine dose size for all petshere
The Rambam’s thoughts on rabies that are still true todayhere
Rabies is one of the oldest recognized diseases of man and animals – everyone knows a bit about it. Rabies is also the most feared of all diseases that humans can catch from animals. The ancients called it hydrophobia because of a mistaken belief that humans suffering from rabies were afraid of water.
The rabies organism is a bullet-shaped RNA virus ,of the genus Lyssavirus in the Rhabdoviridae family. Rabies has a mystique that rests upon its finality and the striking psychological disturbances the disease produces. That is why the ancient Greeks named the virus after their goddess of madness, Lyssa. The stereotypic (typical) foaming mad dog is actually not the commonest form of the disease that veterinarians see.
Fifty years ago, people in the United States usually contracted rabies from their pet dogs and dogs were the largest reservoir of the disease. That was because back then, pet dogs were more common than pet cats, it was uncommon for either dogs or cats to receive periodic preventive rabies vaccinations and dogs were more free to roam. With today’s easy access to effective pet rabies vaccines and public compliance with vaccination laws, the epidemiology (dynamics) of the disease has changed. Now more than 90% of the cases of rabies occur in wildlife – chiefly carnivores and bats. In the developed World, these animals , not dogs, are rabies’ new reservoir.
All warm-blooded animals can catch rabies. In 2012 – the latest published figures available – 6,162 cases of animal rabies were reported in the United States and one human cases occurred. This was a 2.1% increase in the number of animal cases that occurred the previous year and a decrease from the 6 human cases that were reported in 2011. (ref)
Over 90% of the animal cases occurred in wildlife rather than pets. Raccoons constituted 34.8% of the cases, bats – 24.3% of the cases, skunks – 24%, foxes – 7.5%, domestic cats – 4.5%, dogs – 1.25% and cows – 1.1%.
Raccoons are the most common carriers of rabies on the Eastern Seaboard of the United States – from the Atlantic Coast through the Appalachian mountains. They are also the wild animal most likely to mingle with pet dogs and cats – particularly if you feed your pets outside.
Leaving food for your pets outside of the house is something I discourage for a number of reasons, rabies being one of them; exposure to leptospirosis and parasites being others.
In the rest of the Country, skunks are more common carriers. In isolated pockets in Texas, Arizona and Alaska rabid foxes are more common.
In Canada, there were 145 reported cases of rabies in animals in 2009. One human case occurred in 2007 (Alberta) and another in 2003 (British Columbia). Wolves have been know to transmit rabies in Canada, in addition to the same common carrier animals found in the US.
When bats become rabid, it is almost always the large-colony variety that harbor the disease (ie Freetail=Tadarida), not the solitary varieties of bat. Some of these bat colonies number up to 20 million bats and in those colonies, up to 2% show evidence of rabies exposure. (ref)
In 2009, human cases occurred in Texas, Indiana, Virginia and Michigan. In the Texas case, the 17 year-old girl involved was the first known case of complete recovery of an unvaccinated human being from rabies after symptoms had begun. This particular child went on a Texas camping trip two month prior to her illness, during which time several bats collided with her while she explored a cave near the campground. (ref). A partial recovery occurred under similar circumstances in a child in Wisconsin in 2004 (ref)
Hawaii is the only state that has never reported a case of rabies.
The rabies virus attacks the brain causing encephalitis (brain inflammation), which destroys brain cells and ultimately causes death. The early signs of rabies in animals and man are variable and not specific. They can consist of fever, and a general malaise (discomfort, feeling unwell). In humans, a bad headache is often the first sign of the disease. As rabies progresses, neurological (brain-related) signs begin which can include confusion, aimless motion, agitation, blindness, paralysis, salivation, difficulty swallowing and seizures. Patients usually die within the following two weeks.
Although only a few human deaths occur in the United States each year, in southern Asia, many thousands of people die from the disease. Australia, England and Antarctica are the only large geographical areas that are entirely free of rabies. In Europe, the primary carrier of rabies is the fox. In Africa it is the jackal and ,in Asia as well as Puerto Rico (ref) , dogs and mongoose. In South America dogs and vampire bats are known to spread the disease. In the Midwestern United States, skunks are the prime carriers of rabies. Along the Eastern Seaboard, raccoons are the prime carriers. Throughout the US some cases in dogs and humans are derived from contact with foxes and bats.
My Family Or I Were Bitten By a Rabbit, Squirrel Or Our Pet Rodent – Are We In Danger?
The US Center For Disease Control in Atlanta has not recorded a single case of human rabies derived from the bite of a squirrels or other rodent.
Although it is scientifically conceivable for any warm-blooded animal to contract rabies, it is extremely unlikely. I know of no public health official or expert on rabies that would suggest a series of rabies shots after such a bite. You can read the State of Michigan’s directive on exposure to such animals bites here.
What Are Some Factors That Would Put Me More At Risk of Rabies Exposure?
People most likely to handle or be exposed to injured and sick wildlife or stray pets are at the most risk for contracting rabies. An effective vaccine is marketed to immunize these high-risk individuals and I have had many of these shots during my career. The vaccine currently used in the United States to immunize humans is Sanofi-Pasteur’s Imovax® HDCV vaccine. Many years ago, rabies vaccines caused great pain, requiring the injections to be given in the stomach or abdomen. That is no longer the case. Dogs and cats that come into frequent contact with wildlife are also at a higher risk for the disease. Vaccines to protect these pets and their owners are highly effective.
How Is Rabies Transmitted?
Rabies is only transmitted through the saliva of infected animals. Being licked by a possibly rabid animal is not dangerous unless the lick is across raw, broken skin. Kissing an animal will not put you at risk of rabies.
The only , very rare, exceptions are to people or animals that frequent caves with large populations of colony bats. In these bat caves, the virus can become airborne in dust and secretions. It can then be inhaled by passing humans and animals. (ref)
The rabies virus is present in large numbers in the saliva of infected animals. However, not every animal or person bitten by a rabid animal develops the disease. Actually, less than two in ten untreated people bitten by rabid animals develop rabies.
What Are The Symptoms Of Rabies?
The rabies virus leaves the site of the bite and travels slowly through nerves taking 3-8 weeks to reach the brain. (An exceptional case might take twelve month to make this journey) Most animals then go through one or more classical stages before they die from the disease. The incubation period in skunks appears to be longer (ref) leading to the misconception that skunks can become life long healthy carriers of the rabies virus.
Rabies is a very variable disease. Classical or “typical” cases of rabies do not always occur. So just because a pet has or does not have one or more typical symptoms of rabies that I describe is no guarantee that the pet has – or does not have the disease.
In wildlife, the signs can be even more variable. Beware of normally nocturnal wildlife that are visible and out in the daytime, or that appear to have lost their normal fear of humans or that behave in ways that they usually would not.
The Prodromal Phase:
Following infection, the virus enters an eclipse during which its effects on the body are negligible. At the site of the bite the rabies virus enters directly into the peripheral nerves or replicates in tissue at the bite site, entering the nerves later.
In dogs, this phase of the disease typically lasts for two or three days. During the next period the animal often becomes nervous and anxious. It may withdraw from contact and run a fever. Personality changes are common. Friendly dogs may become fearful or aggressive and normally fearful or aggressive dogs may become overly friendly. Some observers say that the site of their bite evidently itches or stings them, because they frequently lick and worry the area. Cats seem to go through this phase more rapidly than dogs.
The “Furious” Phase:
Once the virus has entered the peripheral nerves it is transported via sensory and motor nerve fibers to the brain. The virus also spread from the brain to other highly innervated (highly supplied with nerves) sites including the salivary glands. This is the time the virus is present in the animals saliva and can infect others.
After passing through the prodromal phase dogs and cats pass through a stage characterized by irritability to stimuli of sight and sound.
This stage can last one to seven days. These animals often become restless, aggressive and viscous. I have seen dogs in this phase chew the metal bars of their cage until they injured themselves severely. Dogs and cats in this stage of the disease may roam and wander great distances in an aimless fashion. Eventually these animals become ataxic (wobbly) and may develop seizures and die.
The “Dumb” Phase
This is sometimes called the paralytic phase. Some animals develop this stage after a prodromal or furious period. This is the stage in which the nerves of the head and throat become paralyzed. Animals in this state drool and walk about with their mouth agape. They are unable to swallow. Owners often think their pets in this condition have some object lodged in their throat. During a period of about a week these animals become more and more paralyzed and finally die. Many more dogs pass directly into this stage from the prodromal stage, never developing the furious stage of rabies. Cows in this phase often bellow and extend their necks as if their throat was obstructed. It is common for farmers to attempt to remove a suspected apple or corncob from these animals’ throat and in so doing they become exposed to rabies.
How Is Rabies Diagnosed?
The traditional method of rabies diagnosis requires submitting the suspect animal’s brain to a laboratory for microscopic examination. The pathology of rabies infection includes cellular changes that denote encephalitis (brain inflammation) and myelitis (spinal cord inflammation). Blood vessels within the brain become surrounded with white blood cells (perivascular cuffing). Often, reddish globular inclusion bodies form within the nerve cells (Pyramidal and Purkinje cells) of two portions of the brain, the cerebellum and hippocampus. These inclusions are called Negri bodies. They are diagnostic for rabies.
Is There A Treatment For Rabies?
There is no treatment for rabies. (check the brown type below, as that statement is no longer entirely true) Once the disease is in progress death is inevitable. Other than the two cases I mentioned earlier, there are very few, if any, documented accounts of survival in the literature. If an unvaccinated dog or cat is bitten by a known rabid animal, public health officials generally recommended that the pet be destroyed immediately. If the owner are unwilling to do that the animal should be vaccinated for rabies and placed in strict isolation for 6 month. It should be vaccinated again against rabies one month before release. If the pet is current on its rabies vaccination it should be revaccinated immediately and closely observed for 45 days. Decisions tend to be made on a case-by-case basis and decisions vary depending on the personal inclinations of the official making them.
When a human is suspected of having been bitten by a rabid animals, a combination of the human anti-rabies vaccine produced by Sanofi-Pasteur that I previously mention, with or without the addition of rabies immune globulin (RabIg), is given.
Rabies immune globulin contains antibodies that neutralize the rabies virus immediately, whereas the vaccine requires time to stimulate the body’s own immune response and antibody. So RabIg is often given when time is of the essence or the bite was located on the face or hands.
Veterinarians have always known that only a small portion of non-immunized animals and people who were bitten by a proven rabid animal develop rabies. We were taught that that was because the virus is not always present in the saliva or because teeth were probably wiped clean of saliva and virus by the clothing victims were wearing. But an article in the May 2012 issue of American Journal of Tropical Medicine challenges the notion that rabies is universally fatal and untreatable. Almost 80 % of children in some Peruvian jungle regions are fed upon by vampire bats, common carriers of rabies. In those populations, it appears that many people fully recover from exposure to the virus. ( ref 1 , ref 2)
Preventing Rabies Infection
It is always a good procedure to vigorously scrub and disinfect all animal bites. However, the only certain way to prevent infection is prior vaccination or vaccination subsequent to being bitten. Laws throughout the United States and most other countries require periodic rabies vaccination of your dog and cat. Both modified (attenuated, weakened) live virus and killed virus vaccines are available. Some brands are approved for use in ferrets, horses, cattle and sheep as well as dogs and cats. These vaccines are quite effective and almost never fail. The problem is that less than half of the dogs and only one-in-ten cats in the United States receive their rabies vaccinations when they ought to. Vaccine manufacturers suggest that cats and dogs receive their first rabies inoculation at twelve weeks of age and then again when they are one year old. From then on, some vaccines require yearly booster vaccinations while others protect for three years. I always use three-year vaccines. But even though my vaccines are federally licensed and tested for a three-year duration of immunity, many States require that they be given annually.
Excellent vaccines that I have mentioned previously also exists for people at high risk of animal bites.
Oral rabies vaccination of wildlife with Raboral V-RG® has been used in the United States since 1990. Currently, there are 15 states distributing this oral vaccine for raccoons. It is done in the hope that reducing the incidence of rabies in wildlife will reduce the risk of pet exposure. Texas distributes vaccine baits for gray fox and coyote. There have been nearly 48 million doses of Raboral V-RG® distributed in the U.S. and Canada, and 63 million doses have been dispersed worldwide. This vaccine is a recombinant vaccine made from a living canary pox virus that carries the rabies antigen (protein) on its surface. The vaccine cannot cause rabies because it contains only the non-infective surface proteins of the virus, not the viral nuclear material. Only government entities have access to this oral vaccine.
Are Their Alternatives To Frequent Vaccination For My Pet?
In the United States, how often your pet is required to receive a rabies vaccination booster is regulated by the laws of your individual state. Those laws are often slow to keep up with scientific developments or are just inclined to err on the side of caution when it comes to public health. We now have federally-approved and certified vaccines that protect dogs and cats against rabies for three years. Yet most states still require yearly rabies vaccine boosters. Blood tests exist that can determine that your pet is – or is not – still immune to rabies (the RFFIT test). But it will be up to your state or local public health department to decide if they will accept that test’s results in lieu of vaccination and many do not.
What Have We Learned About Rabies in Ferrets?
Until rather recently, public health authorities regarded domestic ferrets much like wild animals. This began to change as the number of pet ferrets in the United States increased. Merial pharmaceutical company saw an opportunity to test and market their Imrab-3 rabies vaccine line for these pet ferrets as well as for the other species it had been tested on. USDA approval of the vaccine’s use in ferrets was obtained about 1990. Although Imrab-3 is approved for every-three-year use in dogs and cats, it is only licensed for every-year use in ferrets. Studies were not conducted long enough to know how long beyond a year that immunity lasts.
Although the management procedure of a pet ferret that has bitten a human is determined individually by each State, States laws regarding quarantine tend to be quite similar. (ref) It is always wise to read your States quarantine statutes yourself, rather than rely on the advice or direction of an animal warden investigating a bite incident or complaint.
What Happens When Humans Are Bitten?
Whenever an animal bites a human it should be quarantined for a 10-14 day observation period. Alternatively it can be humanely destroyed and its brain sent to a laboratory equipped to do rabies diagnostic tests. This is the only accepted option for non-domestic animals. State law determines the conditions of quarantine. Conditions may differ for vaccinated and non-vaccinated animals. If the biting animal can not be located for quarantine or if it should prove to have been rabid, a series of five inoculations of human immune globulin are generally given. Individuals at high risk of bites usually receive a three shot series of human diploid cell line vaccine to prevent rabies.
Subsequent to an animal bite, the type of post-exposure treatment depends on whether the person had been previously vaccinated against rabies. Unvaccinated people usually receive five, 1-ml doses of human rabies vaccine plus one dose of human rabies immune globulin. If the individual was previously vaccinated for rabies they usually receive two, 1-ml doses of rabies vaccine and no immune globulin. (ref).
Rabies is a serious disease. Laws and procedures are constantly changing and they differ from area to area and State to State. If you or your pet have potentially been exposed to rabies, do not rely on my advice, or any internet advice , to be the most current or to be applicable to your particular situation or locality. Speak to your physician, local veterinarian and animal control supervisor to determine what needs to be done.