Zoonoses (also called zoonotic diseases) are diseases that can be passed from animals to man. Most diseases are species specific. Humans don't catch cat flu despite urban legends to the contrary. Most zoonotic diseases can be avoided through good hygiene - disinfecting areas which have become contaminated, washing hands after handling contaminated items (including cats) and wearing rubber gloves to prevent infectious matter entering skin wounds. The majority of diseases pose no threat to humans and can be treated by your doctor. A few are more dangerous to those with poor immune systems and a very small minority are unquestionably dangerous e.g. rabies.
tion of birds which can cause pneumonia in humans. Although easily cured in healthy adults, it is dangerous to the very young, very elderly and to those with a poor immune system. Psittacosis also causes chlamydial eye and respiratory infections in cats. Ringworm is a fungal skin disease which for most people is more irritating than dangerous, though it can cause scarring (due to constant scratching) and may be of concern to individuals with poor immune systems.
PROTOZOAL DISEASES
Feline strains of coccidia and giardia do not appear to be infectious to humans. Giardia cause diarrhoea in cats and normal precautions should be followed when cleaning up; normally cats and humans are infected by the same source (contaminated water) not by each other. Media attention is sometimes focussed on Toxoplasmosis, a type of coccidia that can cause birth defects in unborn babies. Toxoplasmosis, a disease of cats and other mammalian species, is caused by the protozoan parasite Toxoplasma gondii. Protozoa are single-celled animals and though infection with Toxoplasma is fairly common, actual disease caused by the parasite is relatively rare.
Toxoplasmosis
Cats acquire Toxoplasma infection by ingesting infected prey. The organisms multiply in the wall of the small intestine and produce oocysts, which are then excreted in the faeces for 2-3 weeks. Most cats shed oocysts only once after infection and are then effectively immune. Within 5 days the shed oocysts become infectious to other animals and to humans. Infectious "sporulated oocysts" are highly resistant to environmental conditions and can survive in moist shaded soil or sand for many months. Some Toxoplasma organisms migrate from the cat's intestine to muscle and brain but usually remain dormant. The same migration can also occur in humans. Congenital infection (transmission from mother to foetus) occurs in sheep, goats, and humans.
In humans, toxoplasmosis symptoms may be flu-like, in most cases there are no symptoms. Infection is more serious in individuals with poor immune response. If such people contract toxoplasmosis for the first time it can run riot in the body with the immune system unable to keep it in check. In people who have previously been infected, the dormant tissue cysts are activated. Stress can also activate dormant cysts. Activated tissue cysts can produce millions of toxoplasmas which can lodge in the heart or brain and other major organs.
A study in 2002 has suggested that toxoplasmosis, which some people carry as a latent infection, can have neurological effects such as slowed reaction times. One very controversial idea is that latent toxoplasmosis infection might trigger some forms of schizophrenia. Fuller Torrey (Stanley Medical Research Institute, Maryland, USA) found that schizophrenics were statistically more likely to be cat owners and to have latent toxoplasmosis. Test-tube studies indicated that drugs used to control schizophrenia affected the toxoplasmosis parasite and could explain how the drugs worked. Sceptics point out that the drugs might affect the parasite as a side-effect, rather than a primary effect and that persons genetically pre-disposed to schizophrenia (it is a combination of genetic predisposition and environmental triggers) might also be pre-disposed to liking cats; in addition many people with latent toxoplasmosis do not develop schizophrenia.
A Czech scientist even claimed that toxoplasma gondii may make women reckless and friendly and make men jealous and morose. He suggested that toxoplasmosis in infected women more than doubled their risk of causing a traffic accidents by prolonging their reaction time. meanwhile, he claimed that infected men became quiet, withdrawn, suspicious, jealous and dogmatic (men and women have different brain wiring leading to different effects). None of this has been corrobarated, but if it did turn out to be true, toxoplasmosis could be responsible for up to one million road deaths worldwide, making it second only to malaria in deadliness. It could also be responsible for domestic problems between infected parties. The rest of the scientific world remains highly sceptical since the causes of domestic disputes and road accidents are too many and varied to be pinned down on a single cause.
Congenital infection is of greatest concern in humans; especially in pregnant women who contract toxoplasmosis for the first time while they are pregnant. They may show no symptoms themselves, but the foetus may suffer birth defects including blindness and brain damage. Since most cat-owning women have already been exposed to toxoplasmosis (and hence do not become reinfected), this is uncommon which is why it causes headlines. Most infected babies are born healthy, but with dormant toxoplasmosis cysts, in later life these may lead to reduced vision and loss of sight. In the UK, the total number of babies with congenital toxoplasmosis is approximately ten (out of many thousands).
Cats are not the main source of toxoplasmosis infection in humans. In industrialised nations, poorly cooked meat is a much more significant source of infection, particularly lamb and pork (in many areas of the world, approximately 10% of lamb and 25% of pork products contain Toxoplasma cysts). The vogue for 'rare cooked' meat is part of the problem. Contact with contaminated soil is a major means by which toxoplasmosis is spread - including soil of vegetables. The organism may be present in some unpasteurized dairy products, such as goat's (possibly also sheep's) milk.
Simple hygiene can prevent infection. Avoid undercooked meat and unpasteurised goats milk products. Thorough cooking (70 Centigrade/158 Fahrenheit for 15-30 minutes). Freezing to -20 Centigrade may be effective (there is some argument on this). Garden vegetables should be thoroughly washed to remove soil which may be contaminated. Chopping boards which have been used for raw meat should be washed in hot water before they are used for foods to be eaten raw or for ready-to-eat cooked foods. Other precautions are important to pregnant women (or those trying to become pregnant).
Avoid contact with potentially contaminated soil, or wear rubber gloves. Wash with soap and water afterwards. Do not touch mouth with soil-tainted fingers. Cover children's sandboxes to prevent contamination by cats.
FUNGAL INFECTIONS
Fungal infections of humans are surprisingly common: thrush, athlete's foot etc. The only one of concern in the context of this article is ringworm.
Ringworm
Ringworm is probably the most common zoonosis of cats. Vets who treat ringwormy cats are used to seeing owners with red, scaly, itchy patches of skin. Ringworm is not a worm but a fungus; it normally causes circular scaly patches (which often fluoresce under a Woods Lamp [UV light]). Some strains do not fluoresce and must be cultured in the laboratory to provide a diagnosis. Unfortunately up to 40% of cats may have the fungus without showing any symptoms.
It is a nuisance to eradicate from a household because of fungal spores. Cat treatment is usually by tablet (sometimes by dips or baths). Human treatment is usually by anti-fungal creams. The human version is probably frequently dismissed as eczema by cat owners and left untreated. As with other skin diseases, the red scaly circular patches may be itchy and continued scratching may cause scarring.
BACTERIAL INFECTIONS
Bacteria are usually secondary infectious agents that follow viral or mycobacterial infections. Bacteria may be present in diarrhoea which is an effective means of cross-infection (solid stools buried in litter are less infectious).
Common zoonotic bacteria include species of campylobacter, streptococcus and staphylococci; these generally respond to antibiotic. However, some cat breeders now routinely dose their cats on antibiotics in an attempt to reduce disease in the cattery. This is leading to an increase in antibiotic-resistant strains of bacteria. The problems of resistant bacteria have already been encountered in the livestock/poultry industry, caused by too many animals in too little space and routine dosing with 'preventative' antibiotics.
Feline conjunctivitis can be caused by a variety of conditions including bacterial or viral infections; conjunctivitis caused by a foreign body may lead to a secondary bacterial infection. Since some of these germs can also infect humans, it is wise to observe basic hygiene precautions when handling cats with conjunctivitis. Most cases are easily treated in both cats and humans by eye drops and eye ointments - often containing the same active ingredients!
Persistent streptococcal infections in cats can cause tonsilitis and pharyngitis in the owners.
Pasteurella is possibly the most common bacterial zoonosis, carried in the mouths of up to 75% of cats. Cat bite wounds should be always be cleaned carefully with antiseptic or antibiotic cleansers and an antibiotic ointment applied. Any sign of wound inflammation, persistent swelling or fever should be referred to the doctor as it may require oral antibiotics. Most healthy adults will recover without treatment; but you may not wish to risk your health.
Salmonella bacteria is more common in the faeces of cats fed raw meat or those that catch wild birds. Infection follows a faecal-oral route (you clean the litter tray and scratch your lip without first washing your hands)
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