In general all bites, whatever the attacker, should be thoroughly cleaned and irrigated.  Tetanus prophylaxis should be offered depending on immunisation status and consideration should be given to prescribing antibiotics.

Dog bites

Although human bites are more likely to cause severe infection (because of the wide variety of oral flora), dog bites are far more common. Of those people who are bitten by dogs only the smallest number develop severe life-threatening infection as a direct result of the bite. Those that do may well have been infected with Capnocytophaga canimorsus. It is a gram negative, spore forming anaerobe found in the oral cavity of dogs. Immunocompromised patients are most at risk and, as the bacterium can take a week to incubate, may not become profoundly unwell for some time after the initial insult. At this point they will become systemically unwell with fevers, chills and rigors before developing limb necrosis, multi-organ failure and death. Infection may also be a result of staphylococcusstreptococcus and bacteroides species.

Dog bites can cause substantial soft tissue defects, lacerations and abrasions as well as broken bones and subsequent scarring. Depending on the site that is bitten plastic surgery is often required, firstly to thoroughly clean the wounds and then to obtain cosmesis. In fact, the first partial face transplant was carried out on a woman who was bitten by her pet Labrador. Most cases only require debridement and irrigation followed by a course of amoxycillin/clavulanic acid. In wounds with established infection our local practice is to use piperacillin/tazobactam intravenously.

Do all dog bites need prophylactic antibiotics? A Cochrane review from 2001 suggests not. As is often the case though only 18 trials comprise the database and the control groups (no antibiotics) often had a low rate of infection to begin with so it is difficult to assess the effectiveness of antibiotics. Wounds that are deemed to be of higher risk of infection include deep puncture wounds and those that undergo primary closure.

The injuries are not just physical but mental as well. 50% of children who are bitten enough to require medical attention suffer from a degree of post-traumatic stress disorder (PTSD).

Cat bites

If you would care to read the Journal of Feline Medicine and Surgery you would know that Siamese cats are more likely to be aggressive than other breeds and that the majority of attackers are female. These cats probably have owners with only 31% of reported attacks being by strays or feral cats.

A much larger percentage of cat bites get infected than dog bite, in part due to the fact that they often cause deep puncture wounds that are difficult to clean. Whilst the highest point estimate suggests that up to 18% of canine bites become infected, 18 to 80% of cat bites display signs of infection. It is difficult to know how accurate these figures though as we do not know the denominator. Because cats’ teeth are large needles covered in bacteria they can easily penetrate a joint and cause subsequent infection. It’s worthwhile imaging the bitten part to look for a retained fragment of tooth.

The organism that we most have to be worried about in feline bites is Pasteurella multicida.  It is a gram negative anaerobic coccobacillus found in 90% of cat’s mouths. Infection may also be a result of staphylococcusstreptococcus and bacteroides species.

And what of Catch Scratch Disease – an illness deemed so important that Motorhead sang about it (a cover of the Ted Nugent original). Bartonella henselae causes an indolent infection taking several weeks to appear. What starts out as a small localized pustule at the site of the scratch can lead to painful massive lymphadenopathy. It normally self-resolves but can be much more severe in the immunocompromised host.

Again careful wound care is important but as cat bites are much more susceptible to infection they should all probably received prophylactic antibiotics.

Rodent bites

Not many children get brought to the emergency department because of rodent bites.  US surveillance data suggests that only about 2.4% of animal bites in children are a result of rat or mice bites. These are very rarely pet related but rather the a result of the James Herbert-esque swarms that hide beneath our feet.  Around 1.2% of reported bites come from family favourites – gerbils, hamsters, guinea pigs and rabbits.

The organisms are the typical oral flora so include Streptobacillus monoliformis or Sprillum minus which may lead to Rat Bite Fever. After an incubation period of up to four weeks victims may fall foul of fever, rash and septic arthritis and possibly infective endocarditis.

Rabbit scratches and bites, with the exception of the Killer Rabbit of Caerbannog, only cause infection about 10% of the time as they are generally superficial.  Other rare infections caused by rabbits such as tularaemia, yersiniosis and salmenellosis are much more likely to be transmitted by wild rabbits.

Bite reactions

Bite reactions present in different ways and all depend on the insect/mammal that has bitten the individual.

The most common skin presentation is papular urticaria caused by insects such as mosquitos, fleas, mites, bed bugs and sand flies. The site appears red, raised and often has a white centre with a puncture mark. These typically present over areas of exposed skin, such as legs, arms or face. This rash will be itchy and may last from a few days to weeks, however the redness and raised appearance should settle.

If required topical bite cream can be applied or an oral antihistamine administered to ease the redness, swelling and itchiness. To prevent being bitten protective clothing can be worn and DEET can be applied to the skin.

Bee and wasp stings present in a different way. Initially a local erythematous weal appears that improves within the day followed by a bullous reaction with swelling that can last a few days which are typically painful. It is more common for anaphylaxis to occur with these bites so observe for any early signs.

Consider possible bites from snakes, spiders, mosquitoes, bats or dogs in countries where tropical diseases are prevenient. If this is suspected seek medical attention as soon as possible. Ensure travel history is taken as part of your medical assessment to early identify potential tropical cause.

See Andrew Tagg’s DFTB post on spider bites.