Capnocytophaga and dog bites: Changing disease or more reporting?
I seem to write about this bug a lot - disproportionately for a rare cause of infection - but it just keeps getting attention. Reading the title of a recent article "Woman loses legs, fingers to rare infection from dog bite," it was an easy guess that the infection was caused by Capnocytophaga canimorsus. That's the type of dramatic disease this bug can cause, and as hard as it is to say "lucky" about someone that loses digits or limbs, they are lucky since death rates are very high with this infection.
Capnocytophaga canimorsus is a strange little bacterium. It's found in the mouth of pretty much every dog, so people get exposed to it quite commonly, yet it rarely causes disease. However, when it does cause disease (often after an otherwise inconsequential bite), it's bad.
In the most recent report, a 48 year old woman received some minor bites breaking up a fight between two family dogs. The next night, she had a fever and was vomiting, and things went downhill from there (click here to read the full story). An unusual aspect of this case was that the woman didn't have any of the risk factors that are typically present in a person who gets a Capno infection, such as not having a spleen, being an alcoholic or having an immunosuppressive disease. It is unclear why this bug, which is normally quite innocuous to an otherwise healthy person, almost killed her.
An infectious disease physician at the hospital made a few recommendations:
"If a person experiences a dog or cat bite it’s reasonable to have it examined, especially if it’s swollen, painful or red."
- Pretty good advice. It's never a bad idea to get a bite examined, and in some situations, it should be mandatory (e.g. bites over the hands or face, bites to immunocompromised individuals).
"It’s important for the public to not only closely watch animal bites but also to make sure pets are current on their shots and that the owners are up-to-date on tetanus shots."
- Good general advice, but not really related to Capno.
"Dog owners should use caution when trying to break up a fight between animals, she said. Instead of reaching near a dog’s mouth, pull the tail, she advised."
- I'm not so sure about this one. Grabbing a tail of a fighting dog sounds like a good way to get bitten, although reaching near the mouth of a fighting dog would be just as bad or worse.
"Animals that are the source of such infections don’t need to be euthanized, Mondy said, but the dog that bit Sullins was put down for various reasons, including increasing aggressiveness and concerns about exposing babies in the family to the animal."
- Capnocytophaga should never be a reason to euthanize a dog since basically every dog is a carrier. It doesn't matter if there's a baby in the house or not. If the dog's dangerous because of its biting, that's a different story.
This article, along with various other recent reports, makes me ask a couple of questions:
Are Capnocytophaga canimorsus infections getting more common?
- I don't know. It's possible, as disease trends can change. It could also be that reporters are picking up these cases more often since they tend to be dramatic.
Are more low-risk people becoming infected?
- This one concerns me a bit. Traditionally, when I saw a report of Capnocytophaga in the literature or lay press, I could guarantee I'd eventually come across a statement about the person not having a spleen, or less commonly being an alcoholic or having some other immunocompromising problem. Again, it may just be my impression but I'm seeing more reports where a risk factor isn't apparent. It could be that an immunocompromising problem is there but is not known, but this report, along with some other recent news articles and a published case report, raise concern about the potential for this bug to cause disease in the absence of traditional risk factors.
This doesn't mean owners should fear their dogs, since it's still a very rare problem. However, it re-inforces the need to:
- Reduce the risk of bites through proper training (of both the dog and people who interact with it).
- Use prompt and proper first aid measures after any bite.
- Ensure that people who are at high risk for infection, particularly people without a spleen and those with compromised immune systems, always seek medical attention promptly after a bite.
Dog bite infections in the news
It might just be my perception, but it seems like there are a lot more reports of nasty dog bite infections in the news lately, particularly infections caused by the bacterium Capnocytophaga canimorsus. I don't know whether that's because they are becoming more common, more commonly diagnosed (since the bug is hard to identify), more commonly reported in the press or a combination of all three (or whether my perception is simply incorrect).
The latest report is from Omaha, Nebraska, where a 50-year-old man died four days after suffering a minor dog bite on the cheek. The cause of infection wasn't reported, but the article says that he was unable to fight the infection because he didn't have a spleen. For me, minor bite + fatal infection + no spleen = Capnocytophaga infection until proven otherwise, since this is a textbook description of such an infection, and Capnocytophaga can be found in the mouth of virtually every dog.
This follows the high-profile case of a cancer survivor who lost her hands and feet from Capnocytophaga infection complications and a UK inquest into the death of a man caused by infection with this bacterium, among other cases.
Here are the simple take home messages:
- Avoid bites and any interactions whereby dog saliva may come in contact with non-intact skin.
- Know if you are at high-risk for an infection caused by a bug like Capnocytophaga. This bacterium typically doesn't cause disease in healthy individuals but can produce rapidly fatal disease in certain people.
- Realize that minor bites can cause major problems (even if you are otherwise healthy).
- Use good first aid practices if you or someone you're with is bitten, including careful washing of the wound and seeking medical care if you are at increased risk of infection, or if the bite is over the hands, feet, face, joints or other sensitive areas.
UK dog bite death inquest
An inquest into the dog-bite-associated death of Gary Dickinson, age 57, is underway in the UK. When people think about deaths from dog bites, they usually think about death from severe trauma, especially in kids. However, as I've mentioned repeatedly, minor bites can also pose major risks.
Mr. Dickinson died in February, only three days after being nipped in the finger while breaking up a fight between his dogs. It was a minor bite that many people would quickly dismiss. However, trauma isn't the only possible problem with bites. Infections from bites can be very serious, and in some situations all it takes is a very small break in the skin to allow bacteria to move into the tissues.
Despite suffering no consequences from the initial trauma of the bite, Mr. Dickinson was feeling sick by the next day. He went to the hospital and was sent home with a diagnosis of food poisoning (probably based on vague signs and lack of any other obvious diagnosis, rather than any true evidence of food poisoning. A key question here is whether the dog bite was mentioned at the hospital, which is unclear to me).
Mr. Dickinson deteriorated rapidly after returning home and was rushed back to hospital. Despite aggressive treatment, he died just six hours after admission. The diagnosis was Capnocytophaga infection, and this is a pretty classic picture of this rare but devastating infection.
Capnocytophaga is a type of bacterium that is found in the mouths of dogs. Pretty much every dog has loads of it in the mouth, and people are very commonly exposed through contact with saliva. Fortunately, it rarely causes infections and usually is only a problem in people with compromised immune systems. People who do not have a functional spleen (typically because it has been removed for one reason or another) are the classical high risk group for Capnocytophaga infection. Alcoholics are another high risk group, and that appears to have been the issue in this case.
Minor bites are usually just that - minor. However, sometimes very bad things can happen following very minor bites. Serious consequences are most common in young kids, the elderly and people with compromised immune systems (especially people who have had their spleen removed). While no one should panic after a mild bite, everyone should take any bite seriously. In most situations, thorough cleaning of the wound is adequate, but bites over critical areas (e.g. face, joints, hands) or in high risk people need to be assessed promptly by a physician.
More information about bites can be found on the Worms & Germs Resources - Pets page.
Dog bite death
A 35-year-old UK man has died following a seemingly innocuous dog bite. He was nipped by the family's pet dog, not during an aggressive incident but just a playful, boisterous dog. Later, he developed a fever. He saw a doctor the next day and was told that he had influenza based on his clinical signs, but no testing was done. There's no mention about whether the doctor was notified about the dog bite or asked about animal bites or contact. (I wouldn't be surprised if that didn't happen.)
Unfortunately, the man's condition deteriorated and he was diagnosed with sepsis, which is an overwhelming infection of the bloodstream. A dog-associated bacterium, Capnocytophaga canimorsus, was identified as the cause. Both of the man's leg's were amputated because of the effects of the infection, after which he started to improve, but he later developed more complications and ultimately died.
A doctor explained, "These things are so unusual. It would have been like an unstoppable train – it just depends on how the body reacts." Infection with C. canimorsus is rare, and once it's underway, it can be difficult to control. However, this quote neglects the potential treatable aspect of the infection. For an aggressive infection like this, diagnosing it early is critical. If the doctor had asked about pet contact, asked about bites, noticed the bite, or if the person had mentioned the dog bite at the first visit, an astute physician may have thought about bite-associated infection and hopefully started proper treatment, before fulminant sepsis developed. This would be particularly true for certain high-risk individuals.
Capnocytophaga infections occur almost exclusively in high-risk people, particularly people without a spleen, but also in immunocompromised individuals or alcoholics. There's no mention of whether this person had any of these risk factors, but people who do should know that they are at high risk, see a physician if they are ever bitten by an animal (even if it seems like a very minor bite), and make sure their physician knows about pet contact.
Avoiding Capnocytophaga is essentially impossible if you have a dog. It's carried in the mouths of most (if not all) dogs, but it's typically not an issue. Human infections are rare but they are important because, like in this case, they tend to be very severe when they do occur. High-risk individuals need to know about this bug, make sure their physician knows about any animal contact they have, be proactive to avoid bites and other exposure to dog saliva, thoroughly wash any bites or wounds contaminated with dog saliva, and consult a physician after any bite, regardless of how mild it may seem. Pet owners shouldn't be afraid of Capnocytophaga, but they should be aware of it and various other bite-associated pathogens, do their best to reduce the risk of bites occurring (e.g. proper training of dogs (and kids)), and know how to take care of bites.
Fatal dog bite
The family of a Washington state man is suing a dog owner after the man was bitten and developed a fatal infection. News reports are somewhat sketchy and contain some inconsistent information, but it appears that Kenneth Bock was bitten by Buddy, a coon hound, at his place of work. There are conflicting stories about how the bite occurred. Some reports say that the dog was roaming freely, while the owner's lawyer says Mr. Bock was bitten while reaching into the vehicle where Buddy was sitting. Apparently, the dog had bitten someone else at the same business earlier that day, so it's clear this dog and/or its owner had some issues. Regardless, the bite occurred and blood was drawn, but at the time the bite seemed to be minor. However, Mr. Bock developed a severe infection and died a week later.
Buddy was euthanized a few days after the bite. That in itself is an issue, because any dog that has bitten someone needs to be observed for 10 days to ensure it does not show signs of rabies infection or, if it must be euthanized within 10 days of the bite, the dog needs to be tested for rabies after euthanasia. Mr. Bock was still alive at the time Buddy was euthanized, so Buddy's rabies status should have been confirmed by observation or testing. Any veterinarian euthanizing an animal is required to ask whether the animal has bitten anyone in the last 10 days. None of the reports say whether or not the dog was tested.
The news reports also don't provide much information about the infection. They say that the Mr. Bock had another medical condition that put him at increased risk for infection. It could be that he had lost his spleen and he developed an infection with Capnocytophaga canimorsus. This bacterium, which is present in the mouth of most dogs, almost exclusively causes disease in people that have had their spleen removed (as well as alcoholics) and rapidly fatal infections can ensue. There are also a variety of other conditions that affect the immune system and which can thereby put someone at higher risk for various bacterial infections.
Even innocuous-appearing bites can be bad news. People need to protect themselves from bites, and know what to do if a bite occurs.
- Make sure you know if you are in a high-risk group. If you have a compromised immune system, which includes having had your spleen removed, you need to be aware that you are at particularly high risk for severe complications of any bite. Any high-risk individuals who are bitten should seek prompt medical care.
- Be careful around dogs. This is particularly true for dogs you don't know, dogs that have a history of being aggressive, and dogs that are in a confined space like a car. They may perceive this as a "den" and interpret someone new near them as an intrusion into their space.
- Use common sense if you own a dog that has shown ANY tendency to be aggressive. An aggressive, territorial or fearful dog is not a dog to be taking out in public. Any aggressive tendencies must be addressed immediately.
- Don't take pets to stores. You never know who will be there. There may be people who are very allergic or fearful of dogs. Even if you have the nicest dog on the planet, not everyone wants to be forced to be around it.
No spleen + dog bite = beware
A report from Seattlepi.com is a textbook example of what can happen to certain people after dog bites. Mike Moore tried to break up a fight involving his two dogs and received a minor bite. It barely broke the skin. No big deal, eh? Well, perhaps for most people, but unfortunately not for Mr. Moore.
He cleaned the wound and didn't think much about it. Two days later, he thought he had the flu. The next day, he was worse and went to the hospital. By the time he arrived, "his face and body had a bluish tint" ...never a good sign. When he was being examined, he was asked about the scar on his abdomen and he told the hospital staff it was from his spleen having been removed. They then asked about the bandage on his hand and he mentioned the dog bite. (Insert big ringing bells here!) The article says that the medical staff couldn't pinpoint the problem right away, but hopefully Capnocytophaga was a leading thought. Mr. Moore was critically ill by this point with multiple failing organs. He was admitted to ICU, became septic (overwhelming infection in his bloodstream) and was put on a ventilator. His hand had to be amputated, as did both legs below the knee and three fingers on the remaining hand. But he survived. (Despite the obvious long-term problems, he's very lucky to be alive after such a severe infection).
People that have had their spleens removed or who have non-functional spleens are at much greater risk for various infections, such as Capnocytophaga infections. No one should be allowed to leave a hospital after having their spleen removed without a letter saying, among other things, if you are bitten by a dog, get thee to a physician (pronto)! If you don't have a functioning spleen, make sure you know the risks and how to protect your health.
More information about Capnocytophaga and bites can be found on the Worms & Germs Resources page and in our archives.
No spleen, no pets?
The spleen is an important part of the immune system. It is especially important for fighting off certain types of infections. People who have had their spleen removed or whose spleen is not working properly are therefore at greater risk of some infectious diseases. The risk of infection is highest in the first few years after the spleen is removed or stops functioning, but the risk remains increased for life. In general, people who are immunocompromised (i.e. have a weakened immune system (including lack of a working spleen)) can get sick from microorganisms that would not usually cause illness in other people, and bugs that would only make most people mildly ill can cause severe infections in immunocompromised individuals. This is a particular problem in children. Kids that have their spleen removed are often treated with antibiotics for a few years to help prevent infections.
Infection with Streptococcus pneumoniae and Haemophilus influenzae, which are both common pathogens of humans, are two of the major concerns in people without a functioning spleen. The most commonly discussed zoonotic disease threats in these individuals are the bacterium Capnocytophaga canimorsus and Salmonella. Capnocytophaga lives in the mouth of a large percentage of healthy dogs. Infection in immunocompromised people typically occurs as the result of a bite, but is very rare in other people. There is no indication to test dogs for Capnycytophaga, because it is difficult to identify and we do not know how confident we can be about a negative result (e.g. it may be in the dog's mouth even though it doesn't grow from a sample in the lab).
Here's some general advice for individuals who don't have a working spleen:
- Talk to your physician or an infectious disease specialist about the risks associated with animal contact (including pets).
- In general, you do not need to give up your pets. The risk of infection may be increased, but the risks can be minimized in most situations, and the risks are often outweighed by the beneficial aspects of pet ownership.
- Be wary of any possible exposure to an infectious disease, and be diligent about infection control precautions. If you are bitten by an animal (of any kind), see a doctor as soon as possible.
- Make sure your pets do not touch any open wounds you may have. In particular, do not let a dog lick skin that is damaged in any way. Since Capnycytophaga is commonly carried in the mouths of healthy dogs, licking in general should be discouraged.
- Don't feed your pet raw meat or raw treats, because this increases the risk exposure to Salmonella from your pet's stool.
- Be very careful when handling stool to avoid contaminating yourself or other objects/surfaces. If you have a cat, ideally its litterbox(es) should be changed by someone else.
- Always wash your hands well (and frequently) after contact with pets and pet foods, including dry commercial pet food (kibble).
Dog Bite Septicemia - Capnocytophaga canimorsus
Lots of people have heard of cat scratch fever (an infection caused by Bartonella henselae, which is often transmitted by cat scratches and bites), but dog bite septicemia is a much less familiar condition, although it is equally if not more serious when it occurs. As the name suggests, the infection (caused by the bacterium Capnocytophaga canimorsus) is typically transmitted by dog bites, and causes an infection of the bloodstream, resulting in very serious body-wide illness. The bacteria can also cause other types of infection including meningitis, endocarditis (infection of the heart valves) and rarely ocular infections.
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One study reported that 16% of dogs carried C. canimorsus as part of the normal bacteria in their mouths. Compared to the number of dog bites that occur, C. canimorsus infection is relatively uncommon. Most of the people affected by this bacteria have some kind of predisposing factor, particularly having had their spleen removed (splenectomy), having a weakened immune system, or being an alcoholic. The majority of cases occur in people who have regular close contact with dogs or who were bitten by a dog. Septicemia with C. canimorsus is fatal in approximately 1/3 of cases.
Prompt attention and treatment of dog bites is the best defence against bite-associated infections, including C. canimorsus. The bacteria are typically susceptible to many different antibiotics, but if treatment is delayed too long, the damage to the body may be too severe for the patient to survive.
ALL bite wounds should be taken seriously, and immediately washed thoroughly with lots of soap and water. Consult a physician for any bite on the hand, over a joint or tendon sheath (such as on the wrist or ankle), over any kind of implant or prosthesis, or in the groin area. It is also very important to consult a physician regarding treatment of any bite to a person with a compromised immune system, who has had their spleen removed, or who has any serious underlying chronic disease. Animal bites should also be reported to the local public health department.
More information on bites, much of which is also applicable to dog bites, is available on the Worms & Germs Resources page on the cat bites information sheet.
Picture: Trained attack dog Samo leaps forward toward a decoy's arm wrap as Tech. Sgt. David Adcox restrains him. (USAF Photo archives)
