Cholera is an infectious disease that causes severe diarrhoea. It is usually acquired by consuming contaminated food or water during travel to areas where cholera is common. The greatest danger is the dehydration diarrhoea causes. Following some advice can help prevent this condition.…
What is rabies?
Rabies is a deadly infectious viral disease. You can get rabies by being bitten by an infected animal. Currently at least 55,000 people die worldwide every year of rabies,  mostly in India, Africa and South-East Asia, though rabies was once common all over the world. It is diagnosed in humans by observing the characteristic signs and by laboratory tests. Symptoms include fever, pain and extreme changes in behavior.
Rabies is caused by the rabies virus. It is transmitted between animals and from animals to humans, almost always through bites and rarely through other means.
The virus in the saliva of the infected animal infects the nerve cells in the bitten person, then travels from nerve cell to nerve cell until reaching the spinal cord, the brain and the salivary glands. Replication of the virus within the spinal cord and brain leads to the signs and symptoms (see below) of rabies. The replication within the salivary glands allows it to be transmitted onto others through biting.
Rabies can potentially occur in any mammal. Animals known to transmit rabies include:
- Canines (dogs, foxes, wolves, coyotes, jackals);
- Cows, and;
Other ways of transmission
A person can, in rare cases, become infected with rabies without being bitten. Handling and skinning animal carcasses and eating raw animal meat can also transmit the virus.
Direct human-to-human transmission is very rare and occurs almost only in cases when infected donated organs, particularly corneas, are transplanted into uninfected people. It is possible to catch rabies from an infected person's saliva, so infected people are put in quarantine. There has been no well-documented case of human-to-human infection through biting. 
People who are most at risk of catching rabies are people who live in or are travelling in countries where rabies is still relatively common in animal populations, and who are also more likely to come into contact with infected animals. These can include people who are:
- Living in areas with large bat populations;
- Living in areas with a large wildlife population;
- Frequent campers, and;
- Wildlife animal handlers.
Signs and symptoms
After being bitten, there is an incubation period when symptoms do not appear. It can last from a few days to several years, but is usually about 3-12 weeks.
When symptoms appear, they can include:
- Fever and chills;
- Sore throat;
- Loss of appetite;
- Discomfort and irritability, and;
- Pain, tingling and itching at the site of the bite.
A few days after these initial symptoms, symptoms of the nervous system can appear. These are divided into two different forms, known as furious rabies and paralytic rabies.
Symptoms of furious rabies include:
- Muscle spasms;
- Numbness and tingling;
- Confusion, agitation and slow thinking;
- Delirium and hallucinations;
- Changes in behavior;
- Insomnia, and;
- Fear of water - contact with, or even mention of, water or liquids triggers spasms.
Paralytic rabies appears in about 30% of rabies cases and is more difficult to diagnose correctly.  Symptoms include:
- Muscle weakness;
- Loss of muscle control, and;
- Paralysis, which usually first appears in the hands, then spreads to the rest of the body.
Methods for diagnosis
If a rabies infection is suspected due to an animal bite and/or the appearance of symptoms, it can be diagnosed in humans by observing the characteristic symptoms and by laboratory tests.
Tests for the presence of the virus can be done on several tissues, including:
- Skin (taken from the back of the neck), and;
- Spinal fluid.
The best places for finding the rabies virus are cells of the nervous system. However, taking samples from the nervous system can cause harm, and therefore is generally avoided in humans. To confirm or rule out a rabies diagnosis, a tissue sample can be taken from the biting animal's brain and tested for the presence of the rabies virus. This requires the animal to be put down.
Types of treatment
If bitten or otherwise exposed to the virus, immediate treatment (known as post-exposure prophylaxis, or PEP) is necessary in order to prevent the virus from reaching and infecting nerve cells. This can include:
- Washing and cleaning the bite wound or scratch;
- Vaccination, and;
- Immunoglobulin treatment - antibodies against the rabies virus are injected into the infection site.
This experimental course of treatment was developed in 2004 and saved the life of an unvaccinated teenager infected with rabies. The treatment involves placing the infected person under an artificially-induced coma in order to delay the virus's advance into the brain. The Milwaukee protocol is a last-ditch resort and its chances of success are low.
Once the rabies virus is established in the body, it is almost always fatal. Some cases are reported in which people have recovered from rabies, particularly those who have been exposed to rabies from bats and other non-canine mammals. However, rabies transmitted by infected dogs, foxes and other canines appear to be more virulent and the chances of survival are very low.
The most effective way of reducing the risks of rabies is vaccination. The original rabies vaccine was first administered in 1885 by Louis Pasteur. The vaccine is generally safe and effective. It is recommended for people who are expected to come into contact with wildlife, or are travelling to areas where rabies is found. People who have had the vaccine still need to seek immediate medical care and treatment if they are exposed to rabies.
Another way to reduce the risk of rabies infection is to reduce the number of animals infected with the virus. Most deaths from rabies are the result of dog bites, both stray and domesticated.
Ways of reducing the risk of rabies in animals living in rabies-prone areas include:
- Vaccinating your pet;
- Not letting pets stray outside;
- Avoiding contact with wild animals, particularly dogs, foxes and bats;
- Alerting animal control authorities to any stray animals in your local area, and;
- Carrying out public health programs to vaccinate wildlife and stray animals.