Infectious diseases are caused by bacteria, viruses, protozoa or fungi. These organisms invade the cat’s body. The cat becomes a host and they cause illness. They are all pathogens. They are infectious because they can be transmitted from one cat to another in various ways including contact with infected faeces, mucus, urine, and other bodily secretions. Or pathogens can be inhaled in droplets in the air. Some are transmitted via the genital tract when cats mate and others are acquired when in contact with spores in the soil that enter the body through the respiratory tract or a break in the skin.
Not all pathogens cause an infection. Only a few are contagious. Many infectious diseases are only infectious to a certain species. If a pathogen is infectious to both an animal and a human and can be transmitted between them it is called a zoonotic disease. The same definition is applied to a disease which can be admitted between different species of animal. Many of these infectious agents can survive for a long time outside the host. In controlling the disease this information is useful.
I will very briefly touch on these four headings.
Bacteria are single-celled microorganisms. They can cause the following diseases in cats: salmonella, campylobacteriosis, Clostridium perfringens, tetanus, Helicobacter, tularaemia, plague, tuberculosis, Bordetella, feline pneumonitis (feline chlamydiosis), feline mycoplasma infection, feline infectious anaemias.
The following viral diseases can affect the domestic cat: feline viral respiratory disease complex. They are highly contagious and two major viral groups are responsible for the majority of clinical upper respiratory infections namely herpesvirus group and the calicivirus group, virulent systemic feline calicivirus, feline panleukopenia, feline infectious peritonitis, feline leukaemia virus disease complex commonly described as feline leukaemia virus or for short FeLV, feline immunodeficiency virus and rabies. Viruses are microscopic infectious agents that contain genetic material. They need to invade the cells of the animal or plant to replicate and in doing so the damage the cell and cause illness in the animal.
These include: cryptococcosis, histoplasmosis, sporotrichosis, aspergillosis, blastomycosis.
Protozoa are one celled animals invisible to the naked eye but can be seen under the microscope. They are normally found in water. They have a complicated life cycle. Normally infection results from ingestion of the cyst form of the protozoan. They include: rickettsial diseases which include Bartonella a.k.a. cat scratch disease.
PS: toxoplasmosis is a protozoal parasite. It is not, therefore, listed under infectious diseases. Other protozoan parasites are trichomoniasis, giardiasis and coccidiosis.
If you want to investigate the diseases more you might find some more information by clicking on this link which takes you to a cat health problem page; a very extensive page with lots of links. Alternatively, please use the search facility below and there is another search facility at the heading of the page. There are many articles on cat health problems on this website but they are simply guidelines and meant to be informational. There is no substitute for seeing a veterinarian in a timely manner.
Use this very effective search tool to find further information on most of these diseases. Thanks.
Below are some more articles on viruses.