Starting with the presumption that the scratch and bite are of about equal severity, to answer the question the title I think we have to look at two things:
- The frequency with which bacteria is transferred from cats to people through their teeth compared to through their claws and;
- The ‘potency’ of the bacteria on teeth and claws. By this I mean how dangerous is that bacteria to human health when it is transmitted from cat to person?
Cats’ mouths contain a lot of bacteria as does the mouths of people and of dogs. A study tells me that in a clinically healthy cat the following bacteria are likely to be present: “Porphyromonas, Moraxella, and Fusobacterium are the most abundant genera, and Capnocytophaga canimorsus is the most prevalent species, followed by Xanthomonadaceae and Bergeyella spp.” And in another study, in unhealthy cats, Pasteurella multocida subsp. multocida “were more prevalent compared to controls”.
The issue with cats is that they have quite sharp canine teeth and a strong bite. They can therefore inject their mouth bacteria deep into a person up to the bone and among tendons and ligaments.
Feline mouth bacteria are therefore injected efficiently. Pasteurella multocida, as mentioned above, is a bacterium found in the mouths of between 70-90% of cats according to Cornell, a respected website. It is also found in 50-80% of cat bites in humans when the bite resulted in an infection requiring medical attention.
It seems that this bacterium is the most common and potent with respect cat bites inflicted on people. Bites are more likely to become infected than dog bites because their teeth are sharper than those of dogs. According to one organisation, the American Academy of Paediatrics, infection occurs in up to 50% of cat bites and in 10-50% of dog bites.
A Mayo Clinic study covering three years and reported in 2014 found that one in three patients with cat bites had to be hospitalised. This information surprises me greatly. And two thirds of those hospitalised needed surgery. Middle-aged women were the most common bite victims. Note: I suspect that a lot of the time the victim has allowed the infection to take hold, greatly exacerbating the damage done.
One of the important ways to deal with cat bites is to watch very carefully for signs of infection and then act promptly to squash the infection with antibiotics. This will prevent the need for any further treatment and will certainly preclude the need to go to hospital. See link below.
The Mayo Clinic study covered bites to the hand between January 1, 2009, through to 2011. There were 193 participants, 57 of which were hospitalised on average for three days.
This paints a very severe picture. I don’t think that it is entirely typical, but it is a warning that things can go wrong with cat bites and the Pasteurella multocida bacterium appears to be the villain.
Cat scratches and CSD
With respect to cat scratches, the potency of the bacterium and the chances of it being transmitted from cat to person, the numbers are less alarming. Cornell state that a study found that the average annual incidence of cat scratch disease (CSD) in the US was about 4.5 cases per 100,000 population or about 0.005%. And they found that the disease most often occurred in children between the ages of 5-9 living in the southern states of the USA. This indicates a very low chance of acquiring this bacterial infection.
The bacterium transmitted from a cat’s claws to the recipient person is Bartonella henselae. This bacterium is on cats’ claws because fleas carry the bacteria. Cats ingest fleas and fleas bite cats and deposit the bacteria into the cat. The bacteria are in the cat’s stool, and it can end up on their claws. When the cat scratches the person, the bacteria is transmitted and deposited in the scratch.
Another way of transmitting this disease to people is if a cat licks a person’s open wound or bite. CSD can produce symptoms of low-grade fever, enlarged lymph nodes, a pustule at the side of the scratch, and rarely, infections of various parts of the anatomy including the liver and spleen, and it can cause infection of the heart valves causing endocarditis.
It seems to me on my assessment that the “potency” of the bacteria on cats’ claws is similar to that in the mouth. The defining factor as to whether a cat bite is more dangerous than a cat scratch is the likelihood of acquiring an infection from a cat bite compared to the likelihood of acquiring an infection from a cat scratch. The latter is far rarer than the former and therefore the cat scratch is less dangerous to a person than a cat bite.
Your views are welcome particularly if they differ from mine.
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