There are a number of highly infectious and potentially fatal diseases which can affect your cat. However, for many of these conditions there is a simple protection in the form of vaccinations. Ensuring that your cat completes an initial course of vaccinations and then receives regular booster jabs is important if you want to keep your cat fit and healthy. The 'routine' vaccinations given by your vet will not include protection against all these diseases so it is important to consider the benefits of additional vaccinations on an individual cat basis. Your cat's risk of contracting some of these diseases will depend on its lifestyle.
For some of these infections there is no vaccine available and while treatment may be an option it would be better if you could reduce your cat's risk of coming into contact with these diseases. You should consult with your own vet on the best way to protect your cat's health.
One other point to consider is the risk of you contracting a disease from your cat (a zoonotic disease). This is not a common occurrence, but people with a compromised immune system, eg pregnant women, the elderly or sick children are at particular risk. Cats can carry toxplasmosis. Toxoplasmosis is caused by an infection with a tiny single-celled creature called Toxoplasma gondii. This is a very common parasite in mammals and birds but it can only live through every stage of its complicated life cycle in cats and in most cats this does not cause any signs of illness. Other parasitic diseases can also be passed from cats to people so it is important to care for your cat's health for many reasons.