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Wound licking is an instinctive response in humans and many other animals to lick an injury. Dogs, cats, small rodents and primates all lick wounds. Saliva contains tissue factor which promotes the blood clotting mechanism. The enzyme lysozyme is found in many tissues and is known to attack the cell walls of many gram-positive bacteria, aiding in defense against infection. Tears are also beneficial to wounds due to the lysozyme enzyme. However, there are also infection risks due to bacteria in the human mouth.
It has been long observed that the licking of their wounds by dogs might be beneficial. Indeed, a dog’s saliva is bactericidal against the bacteria Escherichia coli and Streptococcus canis, although not against coagulase positive Staphylococcus or Pseudomonas aeruginosa. Wound licking is also important in other animals. Removal of the salivary glands of mice and rats slows wound healing, and communal licking of wounds among rodents accelerates wound healing. Communal licking is common in several primate species. In macaques, hair surrounding a wound and any dirt is removed, and the wound is licked, healing without infection.
Too much licking of wounds can be harmful. An Elizabethan collar is sometimes worn by pet animals to prevent biting or excessive wound licking, which can cause a lick granuloma. These lesions are often infected by pathogenic bacteria such as Staphylococcus intermedius. Infection is another risk. Horses that lick wounds may become infected by a stomach parasite, Habronema, a type of nematode worm. The rabies virus may be transmitted between kudu antelopes by wound licking.
As with the licking of wounds by people, wound licking by animals carries a risk of infection. Allowing pet cats to lick open wounds can cause cellulitis and septicemia due to bacterial infections. Licking of open wounds by dogs could transmit rabies if the dog is infected with rabies, although this is said by the CDC to be rare. Dog saliva has been reported to complicate the healing of ulcers. Another issue is the possibility of an allergy to proteins in the saliva of pets, such as Fel d 1 in cat allergy and Can f 1 in dog allergy. Cases of serious infection following the licking of wounds by pets include:
- A diabetic man who was infected by Pasteurella dagmatis due to the licking of his injured toe by his dog, causing a spinal infection.
- A woman recovering from knee surgery suffered a persistent infection of the knee with Pasteurella after her dog licked a small wound on her toe.
- A dog lick to an Australian woman’s minor burn caused septicemia and necrosis due to Capnocytophaga canimorsus infection, resulting in the loss of all her toes, fingers and a leg.
- C. canimorsus caused acute renal failure due to septicemia in a man whose open hand wound was licked by his dog.
- A 68-year-old man died from septicemia and necrotizing fasciitis after a wound was licked by his dog.
- A patient with a perforated eardrum developed meningitis after his dog passed on a Pasteurella multocida infection by licking his ear.
- A woman recovering from surgery for endometrial cancer suffered from Pasteurella multocida infection causing an abscess after her cat licked the incision.
- A blood donor whose cat licked her chapped fingers passed on Pasteurella infection to a 74-year-old transfusion recipient.
- A seven-week-old boy contracted meningitis due to Pasteurella from contact with pet saliva.