Posted by: glamielle | January 12, 2012

Rabies, one of the most well known zoonoses remains a significant public health issue worldwide

Hello everyone, I would first like to wish to all of you a great and prosperous year 2012 and I would like to thank all of those who have visited the website as well as supported me and left comments.

I want to start the year talking about one of the most recognized zoonotic diseases in the world: rabies. However, in spite of its somewhat “famous” status, I have observed that some people miss some key facts regarding this disease

As a small animal practitioner, rabies prevention through pet vaccination is a cornerstone of my work and I always take the time to educate clients about the risks posed by the disease, but also proper management of animals to reduce likelihood of transmission to animals and people. As such, I have noticed some discrepancies between what people know about rabies and what I believe are other important points.

Rabies is caused by a virus from the Rhabdoviridae family and it is present generally worldwide except some parts of the world such as Hawaii or New Zealand. Several European countries have also become rabies-free after intensive wildlife vaccination programs.

The Common Vampire Bat is a species of bat often implicated in rabies transmission to livestock in Latin America. (wikipedia.org)

One of the greatest misconceptions comes from the belief that it only affects dogs. However, the virus can be found in virtually every mammal, including dogs, cats, bats, cows, horses, sheep and several wildlife species. In fact, there have been several outbreaks of rabies in livestock recently in cows in Costa Rica and Peru in November and December 2011 as well as in a horse in Colorado in April 2010. Transmission is done by a bite of from an infected animal, when virus particles are inoculated into the muscle of another animal, or human.

Once the virus enters the hosts, it replicates in the muscle and travels to the brain inside neurons. Animals and people affected with rabies can usually show a wide range of neurologic clinical signs such as pain, difficulty walking, lack of coordination, or aggression. Some animals, however, can also exhibit what is known as “dumb rabies”, showing signs of depression and lethargy. The disease is progressive in nature and as more organs become affected, patients can also exhibit difficulty swallowing (commonly recognized as fear of water) and sensitivity to light. Patients eventually die from asphyxiation as their respiratory muscles stop working. Clinical signs in animals in people can appear between 10 days to several months after being bitten.

Pets can be exposed to rabies when they come into contact with wild animals such as this skunk. (http://www.globalanimal.org)

There is virtually no treatment against rabies, and affected animals are usually required to be euthanized to protect human health as  well as prevent unnecessary suffering of the patient. Treatment options in people who have been bitten by an unvaccinated animal are also scarce, usually limited to post-exposure prophylaxis (PEP). Essentially, PEP is injection of hyper-immune serum into the wound of an infected person to prevent further virus replication. For this to work, timing is critical and once the virus has entered the nerves, PEP will be of little use. This is why those who have been bitten must go to the hospital as soon as possible to receive PEP treatment. Once people start exhibiting symptoms, prognosis is very poor and these individuals will unfortunately most likely die. There has been a newly developed treatment protocol known as the Milwaukee Protocol that has had some success in treating and curing a handful of people showing symptoms of rabies. This treatment is, however, very challenging and requires the affected person to be put in a coma for a long time. There has been to date only 6 people who have survived rabies using this or similar protocol and if we compare with the number of infected people in the world (about 50 000), the mortality rate for rabies remains approximately 100%.

Rabies has been known for hundreds of years and was one of the first diseases to which a vaccine was created in the 1800s by Louis Pasteur. However, the virus remains prevalent worldwide and affects about 50 000 people yearly. As with many zoonotic diseases, the developing world can be more severely affected and some risk factors for rabies in animals and people include: large population of stray dogs and cats, dog fighting, or close contact between humans and wildlife.

However, rabies can also cause problems in developed countries. An article published in the Journal of the American Veterinary Medical Association (JAVMA) compiled all rabies cases (human and animals) for the year 2010 in the USA. Rabies in pets is usually well controlled in this country, however, several other species of animals can host the disease in the wild, depending on geographical location. The East Coast of the US is characterized by raccoon hosts while on the West Coast, skunks predominate. In other parts of the countries, foxes are also known to harbor the disease. During the year 2010, there has been several reported cases of rabies in domestic animals: 303 cats, 71 cattle, 69 dogs, 37 horses and 6 goats/sheep. Looking at these numbers, it is obvious that the major misconception that dogs only can be affected by the disease doesn’t hold as canine cases come in third place after cats and cattle. It is also important to remember that all these animals are potentially sources of the disease in people. Reported cases in wildlife included raccoons (2246), skunks (1448), bats (1430), foxes (429) and rodents/rabbits (33). These numbers represent the reported cases, meaning that these animals were submitted to laboratory for testing, thus it is likely that the actual numbers were higher. Finally, there have been 2 cases of human rabies during 2010, both fatal. One case was seen in a migrant worker in Louisiana who had been bitten by a vampire bat in Mexico about 10 days before showing symptoms of rabies. The second case was a man in Wisconsin who was hospitalized with difficulty swallowing. Viral testing revealed a strain commonly seen in bats of the area.

Distribution of wildlife terrestrial hosts of rabies. Bats are not terrestrial animals and are not depicted on this map. (http://www.cdc.gov)

It is important to notice that both of these people were infected after being bitten by bats, thus showing how important this species is when it comes to zoonotic transmission of rabies. In fact, the latest case of rabies in the US was seen in Massachusetts over the end of December 2011. The patient started exhibiting neurologic signs after having been bitten by a bat (once again) and is currently (as of January 2012 when this post was written) hospitalized in critical condition. This is the first case of human rabies in Massachusetts in over 70 years. These cases remind us that, while in many parts of the US, canine rabies cases have gone down, bats are often the most important vector for human rabies.

Considering the severity of the disease, there are several guidelines that people should follow to reduce their likelihood of infection. One of the most important is to stay away from wildlife, especially those animals that are exhibiting strange behavior including aggression or absence of fear. As previously mentioned, bats play a very important role in transmission of rabies and should not be handled by people who are not qualified. Animal control authorities should be called if someone notices a bat in their house. These animals  have small sharp needle-like teeth so bites can often go unnoticed.

There are good vaccines available against rabies, both in animals and people, and those in close contact with animals should definitely be up to date on rabies vaccination. These include people working in veterinary clinics, animal shelters and, in my opinion, livestock workers as well. Likewise, all cats and dogs should be current on their vaccines. Some cat owners may feel that their indoor cat is not at risk of contracting rabies compared to animals that go outside regularly. While that may be true, the severity of the disease warrants strong preventive measures to be put in place in order to protect pets and animal owners alike. In some instances indoor cats may find their way outdoors accidentally and become exposed to rabies. Also, it is not uncommon for bats to be able to enter homes and cats can be attracted by a bat struggling on the floor of a home.

Unvaccinated animals biting people or other pets must be put under strict quarantine or euthanized. (http://www.ccac.ca)

In fact, the diagnosis of rabies in animals usually involves some significantly drastic measures and the issue arises if an unvaccinated  pet/animal bites a person. Laws of different cities/countries may differ on the subject, however, they do follow the same general guidelines. If an unvaccinated animal bites a person, that pet may be required to be put in quarantine at the owner’s expense or even be euthanized in order to submit the brain for laboratory analysis. Maintaining appropriate vaccination status in pets is an easy and simple way to prevent such measures to be taken to protect the public.

In many countries, especially in the developing world, rabies is maintained by stray dogs and cat populations. It is therefore also important to take steps to reduce stray animal numbers and spaying/neutering pets is a great way to achieve that.

Finally, just as in any public health issue, population education is essential to ensure that the public is aware of the risks caused by rabies and the steps they can take to reduce the incidence of the disease in both animals and people.

Dog vaccination programs help greatly in managing rabies in developing countries. (http://www.rabiescontrol.net)

For more information on rabies:

World Health Organization – Rabies

Centers for Disease Control and Prevention – Rabies

Los Angeles County Veterinary Public Health – Rabies control manual

Rabinowitz PM & Conti LA. 2010. Human-Animal Medicine. Saunders Elseviers ed.

Advertisements

Responses

  1. […] The 2nd reason why reporting bites is crucial is for rabies prevention. The veterinary staff at VPH puts a lot of effort in following through on each bite report to make sure the animal is properly quarantined and monitors if there is any signs of the disease. While rabies in dogs has become very rare in LA county, the severity of the disease warrants extreme precautionary measures to make sure people are not exposed (For more information about rabies, check out my previous post). […]


Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

Categories

%d bloggers like this: