The Role of Bacterial Infections in Cat Bites

Introduction

Figure 1. A black cat named Luna opens his mouth wide, revealing his teeth. Photo by Mercer Thomas.

Cats (Felis catus) are domestic or house cats that may live with and around people as pets or working animals. Cats are mammals with four limbs. They vary in size but are relatively small. They may also be feral, meaning that they are a domesticated cat that is unused to or refuses human companionship and interaction.

Cat bites are the bites that occur when a cat bites another living organism. For the purpose of understanding bacterial infections in cat bite wounds, “bites,” on this page, will be understood to mean when cats break the skin of another organism, resulting in puncture wounds of varying sizes, rather than when cats bite or grab another organism between their teeth without breaking the skin as an act of play. Cats often bite other cats, humans, and other mammals or birds. Cats may bite other smaller organisms, such as rodents or small birds, in order to kill them. They may also bite other cats in combat. Cats most often bite humans when they are threatened or scared in an attempt to escape or defend themselves.

Genetics

Figure 2. Graph and visual comparisons of proteins expressed in extracellular matrix (ECM) genes (Collagen type 1 (COL1), Keratin 16 (KRT16), and Tenascin (TENC)) and Wnt pathway genes (Wnt inhibitory factor 1 (WIF1) and Follistatin (FST)). The gene expression plots demonstrate how the proteins are differently expressed in incisors, canines, and pre-molars, respectively, while the imaging demonstrates the spatialized locations of the proteins across the three tooth types.

Cats have three morphologically separate types of teeth: incisors, canines, and premolars. Research suggests that the different developmental timings and physical expressions of the teeth are reflected in the genetic code of each type. Each type has its own transcriptional profile. The three gene groups that differ in terms of expression between teeth types are extracellular matrix (ECM) genes, Wnt pathway signaling genes, and several different homeobox families of genes.

The study, published in 2022, is the first to fully document the embryonic development of cat teeth, and its results suggest that the different expressions of the three types of genes reflect the different developmental timing and structures of each tooth type. The canine, which is the most significant tooth in terms of causing bacterial infections resulting from cat bites, develops along with the large upper premolar, and both develop slightly more quickly than the incisors and much more quickly than the three smaller upper premolars. The study indicates that this timing may be so that the canine and large premolar can fully form before emerging from the gums and that the two smaller upper premolars may develop much later because they are not functional in chewing and, therefore, may have less selective pressure in developmental timing.

Oral Bacterial Microbiome of Cats

According to a recent study that set out to establish the beginning of a feline oral microbiome taxonomic database using a provisional 16S rRNA gene-based taxonomy with full-length reference sequences, there are at least 171 distinct taxa for feline oral bacteria, though they noted that there are likely hundreds more to be identified in the future which they could not identify at the species level. The oral microbiome of cats is polymicrobial because they have many different aerobic and anaerobic microorganisms, and both kinds of microorganisms are often found in wounds from cat bites. This is consistent with the bacterial microorganisms found in cat bite wounds, as a 2014 study of the bacteriology of cat bites found that, on average, there are six bacterial isolates per bite and that 63% of these cultures are polymicrobial.

Hospitalization Resulting from Infection

Cat bites are less common than dog bites in humans, yet cat bites account for much higher rates of hospitalization. In 2020, only 3.5% of patients visiting emergency rooms for dog bite treatments were hospitalized, while 11.7% of those bitten by cats were. This percentage is even higher for patients bitten on the hand or wrist. In a Mayo Clinic study from 2014, of the patients that went to the emergency room for cat bite injuries to the hand (the most common place humans are bitten by cats), 29.53% percent were hospitalized. The average length of hospital stay was just over three days, and of hospitalized patients, 66.67% needed their wounds irrigated and debrided.

They suggest that the higher rates of infection are due both to the bacteria present in cat’s oral microbiome and also to the structure of their teeth. The study found that the bacterial microbiome, while different from that of dogs, is not necessarily more infectious. Instead, hand surgeons suggest that because cats have sharp teeth and tend to inflict relatively deep wounds, they are more likely to leave bacteria in places more susceptible to serious infection, such as joints or tendon sheaths. They also found that the wounds of patients who were hospitalized were often characterized by erythema and swelling.

Conclusion

Humans are prone to cat bites because they tend to get bitten on the hand and because the structure of cats' teeth, particularly their canines, allow them to bite sharply and deeply, reaching joints and tendon sheaths, which are less resistant to infection than the soft tissue reached in shallower bites. Many recent studies indicate that cats' oral microbiomes contain hundreds of different microorganisms and that genetic testing and RNA taxonomic mapping are key to increasing our understanding of cats and their bites and the connection of both to human health and disease.

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Edited by [Author Name], student of Joan Slonczewski for BIOL 116, 2024, Kenyon College.