Rabies

Rabies: Causes, Diagnosis and Management.

Definition



Rabies is an acute viral disease which causes fatal encephalomyelitis in virtually all the warm blooded animals including man. The virus is found in wild and some domestic animals, and is transmitted to other animals and to humans through their saliva (i.e. bites, scratches, licks on broken skin and mucous membrane).
The rabies virus is a lyssavirus, a group of viruses responsible for causing encephalitis that also includes several recently identified bat lyssaviruses. Lyssaviruses belong to the family Rhabdoviridae. The name Rhabdo comes from the Greek and identifies the characteristic bullet or rod-shape of the viruses. There are several strains of the classic rabies virus that are each generally confined to a major species as reservoir.

Transmission

Rabies is usually caused by a bite from an infected mammal. The virus is introduced through the skin or mucus membrane .The virus attacks nervous tissue, it begins to replicate in the muscle, at the wound site. This can go on for hours or weeks. The incubation period of rabies in humans is generally 20–60 days. However, fulminant disease can become symptomatic within 5–6 days.
Alternatively, it may migrate directly to the nervous system connecting at the sensory nerve endings at the inoculation site. Migration to the nervous system is via the nearest sensory or motor neuron in the ganglion at the base of the spinal cord where it continues to replicate. At this time it may be transported back to the wound or to the brain via the CNS. The virus infects neurons in almost all brain regions with continuing replication. Acetylcholine receptors, gangliosides and phospholipids are possible receptors for the virus.
Aerosol transmission, occurs when the virus enters the body through nasal epithelium and is transported to the olfactory bulb. It is though the virus replicates in the neurons of the olfactory bulb before spreading to the brain.
After the brain is infected, it spreads throughout the body via efferent neural pathways. At this stage, the virus may be found in salivary glands tears, skin, adrenal glands, heart muscle, hair follicles and kidneys. The virus has never been found in blood or blood cells. Death from rabies is not a result of structural damage caused by the virus but by functional alterations of neurons.
The rabies RNA and host RNA competes, impairing neural function, exacerbated by certain cytokines as well as, nitric oxide, given off by the body’s immune system in response to the rabies virus acting as a CNS toxin.

History

Rabies, from the Latin word “to rage,” has been recognized for over 4000 years. In the 16th century, an Italian physician Girolamo Fracastoro discovered that rabies was a fatal disease affecting humans as well as animals, calling it “an incurable wound”.
However, it was Louis Pasteur a French biologist that created the first vaccine in 1885. Joseph Meister was a 9-year old boy-at the time. When his parents found out a rabid dog had bitten him, they went to Pasteur begging him to help their son. Pasteur thought if he injected a weak form of the virus from one rabid animal to another, the second animal might be able to help fight off the disease. This experiment worked for Joseph. This was the beginning of the highly effective vaccines we have today.

Epidemiology

Rabies is more prevalent in the developing world than in industrialized countries. The World Health Organization (WHO) estimates that rabies is responsible for 35,000-50,000 deaths annually worldwide and that gross underreporting is likely. An estimated 10 million people receive post exposure prophylaxis each year after being exposed to animals with suspected rabies. Unvaccinated dogs are the major reservoir for rabies.
Global reservoirs of rabies virus are as follows:
  • Europe – Foxes, bats
  • Middle East – Wolves, dogs
  • Asia – Dogs
  • Africa – Dogs, mongooses, antelopes
  • North America – Foxes, skunks, raccoons, insectivorous bats
  • South America – Dogs, vampire bats

How Do People Catch Rabies?

Animals with rabies transfer the virus to other animals and to people via saliva following a bite or via a scratch. However, any contact with the mucous membranes or an open wound can also spread the virus. The transmission of this virus is considered to be exclusively from animal to animal and animal to human. While human-to-human transmission of the virus is extremely rare, there have been a handful of cases reported following transplantation of corneas. For humans who contract rabies, a bite from an unvaccinated dog is by far the most common culprit.
High-risk animals include:
  • Bats
  • Raccoons
  • Foxes
  • Skunks
  • Woodchucks
  • Non-domesticated (wild) dogs
  • Domestic animals like cats, dogs, and cattle can become rabid if bitten, so it is important to vaccinate them against rabies.

Risk factors

Factors that can increase your risk of rabies include:
  • Traveling or living in developing countries where rabies is more common, including countries in Africa and Southeast Asia
  • Activities that are likely to put you in contact with wild animals that may have rabies, such as exploring caves where bats live or camping without taking precautions to keep wild animals away from your campsite
  • Working in a laboratory with the rabies virus
  • Wounds to the head or neck, which may help the rabies virus travel to your brain more quickly

Symptoms

The first symptoms of rabies may be very similar to the flu and may last for days. Later signs and symptoms may include:
  • Fever
  • Headache
  • Nausea
  • Vomiting
  • Agitation
  • Anxiety
  • Confusion
  • High level of excitement
  • Hyperactivity
  • Difficulty swallowing
  • Muscle cramps
  • Excessive salivation
  • Fear of water (hydrophobia) because of the difficulty in swallowing
  • Hallucinations
  • Insomnia
  • Partial paralysis

Complications

  • Increased pressure within the skull (intracranial pressure)
  • Irregular heartbeats (cardiac arrhythmias)
  • Seizures
  • Respiratory failure
  • Acute renal failure
  • Congestive heart failure
  • Gastrointestinal hemorrhage
  • Coma

Exams and Tests

  • If an animal bites you, try to gather as much information about the animal as possible. Call your local animal control authorities to safely capture the animal. If rabies is suspected, the animal will be watched for signs of rabies.
  • A special test called immunofluorescence is used to look at the brain tissue after an animal is dead. This test can reveal whether or not the animal had rabies.
  • The doctor or nurse will examine you and look at the bite. The wound will be cleaned and treated as appropriate.
  • The same test used on animals can be done to check for rabies in humans, using a piece of skin from the neck. Doctors may also look for the rabies virus in your saliva or spinal fluid, although these tests are not as sensitive and may need to be repeated.
  • A spinal tap may be done to look for signs of the infection in your spinal fluid

Treatment for rabies

Post-exposure prophylaxis (PEP)
Post-exposure prophylaxis (PEP) is the immediate treatment of a bite victim after rabies exposure. This prevents virus entry into the central nervous system, which results in imminent death. PEP consists of:
  • Extensive washing and local treatment of the wound as soon as possible after exposure;
  • A course of potent and effective rabies vaccine that meets WHO standards; and
  • The administration of rabies immunoglobulin (RIG), if indicated.
As soon as a bite is received, a series of shots will be prescribed to prevent the virus from thriving. The shots include:
  • A fast-acting shot consisting of rabies immune globulin; this will prevent the virus from infecting the individual and will be delivered as soon as possible, close to the bite wound.
  • A series of rabies vaccines to train your body to fight the virus whenever it finds it. These will be given over the following 2 weeks and delivered into the arm.
There are three vaccines in current use approved by the FDA.
  • Human diploid cell vaccine (HDCV) or Imovax-most widely used
  • Michigan Biologic Products Institute (monkey cell cultures)
  • Inactivated diploid cell origin (DCO)
In most cases, finding out whether the animal has rabies will not be possible. It is safest to assume the worst and begin the course of shots.
Extensive wound washing
This involves first-aid of the wound that includes immediate and thorough flushing and washing of the wound for a minimum of 15 minutes with soap and water, detergent, povidone iodine or other substances that kill the rabies virus.

Prevention

You can prevent being infected with the rabies virus by remembering these tips:
  • Do not feed wild animals and stay at a safe distance when observing them
  • Supervise children and teach them not to approach or touch animals they do not know
  • Stay away from animals showing signs of rabies
  • Do not bring home wild animals
  • If you suspect an animal is rabid, stay away from it and contact the local authorities
  • If you have pets or livestock, make sure to vaccinate them against rabies
  • Wash wounds with soap and water and maintain good hygiene.