Why A Dogs Bite Is Worse Than Its Bark...?

Every year 55,000 people worldwide die from the rabies virus. Rabies is an enzootic virus, prevalent in certain animal populations mainly within Asia and Africa. However, it is also a zoonotic virus, and can be transmitted from animals to humans when infected saliva enters the human host, most often via a bite or scratch.

Transmission is usually from infected dogs, however bats are commonly implicated in the Americas. Other animals known to have passed the virus onto humans include: foxes, racoons, skunks, jackals, and mongooses. Different species carry different strains of the virus; the strain carried by dogs is most fatal to humans.

Once within a host the virus proliferates and spreadsto the central nervous system, effecting the brain and spinal cord. Infection spreads next to the salivary glands, lungs, and kidneys before propagating to other organs. 80% of advanced cases manifest as furious rabies. The patient exhibits sporadic periods of hyperactive and odd behaviour, including: aggression, hallucinations and delusions. These symptoms are due to inflammation of the thalamus and hypothalamus of the brain.

A characteristic symptom of rabies is foaming at the mouth, this is caused by throat spasms and associated hydrophobia. On attempting to swallow, the throat muscles convulse and the sufferer develops an intense fear of water. Further spasms are then brought on by even the sight or sound of water.

The time from infection to appearance of symptoms varies widely but is usually 1-3 months. The closer the site of infection to the brain, the shorter the incubation period; symptoms can develop in as little as a week due to infection in the head, face, or neck. Once advanced symptoms manifest, death by cardio-respiratory arrest occurs within a few days, as neurochemical signalling regulating heart rate and breathing is interrupted.

The rabies vaccine, developed by Louis Pasteur in 1885, is 100% effective in rabies prevention. It can also be given after exposure along with immunoglobins and sterilisation of the wound as part of a treatment called post-exposure prophylaxis (PEP). PEP is usually effective in stopping the spread of the infection.

Rabies is the only human virus thought to prove 100% fatal in advanced cases, however an experimental technique - the Milwaukee Protocol - has been used to treat patients with established infections. The sufferer is put into an induced coma to protect the brain whilst the immune system fights against the virus. As of August 2013, this protocol had been used on 41 patients, of whom only 6 survived. This has led to skepticism over the technique. Some scientists suggest the Milwaukee Protocol itself is not a factor in recovery, rather it is due to the individuals immune system activity and virulence of the rabies strain in each case.

The recent increase in human rabies deaths in Africa, Asia and Latin America, shows rabies poses a serious human health risk. The only way to eradicate the virus is stringent vaccination procedures in animal populations.