Clostridium difficile in the household environment
Another study we presented at the recent European Conference of Clinical Microbiology and Infectious Diseases was about Clostridium difficile in the household environment. In the study, we collected samples from various locations and surfaces in households, as well as five fecal samples (one per day) from pets, and tested them for C. difficile. Some of the most interesting findings included:
Clostridium difficile was found in one or more locations in 31% of households. The toilet was, not surprisingly, the most common site, but the kitchen sink, refrigerator and dog food bowl were close behind.- The most common strain found in households was the international outbreak strain ribotype 027. Ribotype 078, a strain that is commonly found in food and food animals, was the second most common type.
- Clostridium difficile was isolated from 10% of dogs and 10% of cats, however in most cases only 1 of the 5 daily samples was positive.
- All of the strains of C. difficile found in pets were strains that have previously been recovered from people. This fits with previous reports that strains found in animals tend to be the same as those found in people, and supports concerns that C. difficile can be transmitted between humans and animals.
- In no households were C. difficile strains found in the pets the same as those found in the environment. This suggests that pets are not an important source of household C. difficile contamination.
- Dogs that lived with an immunocompromised person were 7.9 times as likely to shed C. difficile than other dogs. Presumably, immunocompromised people are more likely to carry C. difficile and subsequently transmit it to their pets.
More information about Clostridium difficile can be found on the Worms & Germs Resources page.
Rhodococcus equi in horses and people
Rhodococcus equi is a very well recognized pathogen in horses – it is a common cause of pneumonia in foals between the ages of 1-6 months, and infection is also sometimes associated with other problems such as diarrhea, swollen joints and abscesses in other parts of the body. The infection can be very difficult to treat because the bacteria are able to live inside white blood cells, which helps protect them from the body’s immune system, and because they often cause abscesses to form, which are difficult for antibiotics to penetrate. Rhodococcus equi infection in foals has been studied extensively, but there’s still a lot we don’t know how the body defends itself against this organism. These are a few things we do know:
- Almost all foals are exposed to R. equi as neonates, but most of them never develop signs of infection.
- Giving newborn foals hyperimmune plasma (plasma with extra antibodies against R. equi) may have some beneficial effects on farms where the infection is a recurrent problem, but this practice is still controversial.
- Adult horses are essentially immune to the infection.
- In almost all cases if clinical disease in foals, the R. equi strain involved carries a special gene called vapA.
- Mortality rates in foals vary considerably from 0% to 30%.
- So far, efforts to develop a vaccine to help protect foals have been unsuccessful, but research in this area is ongoing.
People can also be infected with R. equi, and as in foals, pyogranulomatous pneumonia (infection of the lungs which results in the formation of many abscesses) is one of the most common conditions caused by this organism. However, there are a few important differences between infection in people and infection in horses:
- 85% to 90% of people with R. equi infection are immunocompromised, meaning their immune system is weakened or suppressed for some reason, e.g. HIV infection, or immunosuppressive drugs taken by organ transplant or cancer patients.
- Among people infected with R. equi who have normal immune systems (i.e. immunocompetent), about half of the infections are localized, meaning they only affect one small part of the body. Many of these are associated with wound infections.
- Only 20% to 25% of the R. equi isolates in people carry the vapA gene.
- Infection in immunocompetent people can be fatal in approximately 11% of cases, but among HIV-infected patients the mortality rate from R. equi infection can be as high as 50% to 55%.
Rhodococcus equi is actually a soil organism, and this is likely the most common source of the organism for both horses and people. Only approximately 1/3 of humans infected with R. equi report that they have had contact with horses or pigs (pigs can also carry the bacterium). So we don't know how much of a risk an infected foal is to a person. However, it is prudent for people, particularly those with weakened immune systems, to take precautions to avoid potential transmission of R. equi from horses.
- Try to reduce dust levels on the farm. Because R. equi most often lives in the soil, it can get stirred up into the air in dusty areas, which can then lead to inhalation by animals and people. Doing things like planting grass or other vegetation, installing windbreaks in high-traffic areas, or wetting down dusty stalls or paddocks can help reduce dust levels in the air.
- Keep open wounds and other broken skin covered when working around animals.
- Always wash your hands after handling a foal (or any horse)
- If you have a foal that develops signs of R. equi infection, make sure you have your veterinarian examine it as soon as possible so the diagnosis can be determined and the foal can be treated properly as soon as possible. Some foals with R. equi may develop severe pneumonia very quickly, so it’s important that they are examined right away.
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).
Baby accidents and dog baths
Recently I was having a discussion with a reporter about cleaning and disinfection, and the reported mentioned that her child had pooped in the bathtub the other day. My response was "mine too", since coincidentally, my 17-month-old daughter did the same thing on the same day. We discussed about what to do with the bathtub, and it lead me to thinking about issues regarding bathing pets in bathtubs.
I'm not sure I've ever given my dog a bath in the bathtub, but some people do. I've never seen any recommendations about infection control practices associated with dog-washing or an assessment of the possible risks involved. Since there are lots of bacteria that live on or in pets (and people), and some of these can cause disease in certain situations, it's something worth considering. Overall, the risks from a healthy pet in a household full of healthy people are probably exceedingly low. There are, however some situations where risks might be higher.
Pet factors that may increase the risk of disease transmission to people if they bathe in the same tub include:
- Diarrhea
- Wounds or skin infection
- Contamination of the hair coat with feces
- Young puppies or kittens, since they are more likely to be carrying certain infectious bacteria or parasites
People that are probably at higher risk of infection if they use the same tub as a pet include those who:
- Have open skin lesions/wounds or chronic skin disease
- Are immunocompromised
- Are very young or very old
- Are pregnant
It's probably best to avoid bathing pets in the bathtub (and certainly don't bathe them in the kitchen sink!!), if possible. Bathing pets outside or in the laundry room sink are better ideas, although they're not always practical. If you are going to bath your pet in the bathtub, here's what I'd recommend:
- Ensure the pet is healthy.
- Remove items from the area around the tub that might become contaminated (e.g. wash cloths, shampoo bottles, kids' bath toys).
- After the bath, use soap and water to clean the tub, walls and other areas that may have been splashed.
- Rinse all surfaces thoroughly with hot water.
- Allow all surfaces to dry completely.
I'm not sure a disinfectant is really needed in most cases, but it probably wouldn't hurt. If used, a disinfectant (like diluted household bleach) could be sprayed or wiped onto surfaces after cleaning. It should be allowed to sit for at least 15 minutes. Immediately wiping off the disinfectant greatly decreases the chance of it having any effect.
If you have a high risk pet or high risk person in the household, I'd be very careful. The best thing would be to bathe the pet elsewhere, either outside or take it to a at a vet clinic or pet groomer. If you do bathe your animal in the tub in this situation, be especially thorough about cleaning the tub afterwards, and definitely apply a disinfectant.
Cat Scratch Disease - Bartonella henselae
Bartonella henselae is a small, Gram-negative bacterium that is host-adapted to cats. It may rarely cause mild illness in cats, but most felines, from tiny house cats to the king of the beasts, carry the bacteria with no clinical signs whatsoever. Unfortunately, when B. henselae infects a person it can cause any of several serious conditions (most of which have very long names!). These include bacillary angiomatosis (formation of masses of abnormal blood and lymph vessels), endocarditis (infection of the lining of the heart), chronic lymphadomegally (enlarged lymph nodes), and pyogranulomatous lymphadenitis, better known as cat scratch disease. There are at least four Bartonella species (among many, many other Bartonella species) that can infect cats, but B. henselae is the most common. There are at least nine Bartonella species that can infect humans, seven of which are zoonotic.
Between 5% and 40% of cats in the USA have B. henselae in their bloodstream. It is most common in cats from temperate areas, and is much less common in Canada. Bartonella spp. live in the red blood cells of their host – quite a clever strategy really, because it makes the bacteria readily available to be picked up by vectors like blood-sucking fleas, it protects the bacteria from the hosts immune system so it can live there for a long time, and it may even partially protect the bacteria from antibiotics. Cats can maintain a waxing and waning infection for months or even years. The bacterium is transmitted between animals by the cat flea (Ctenocephalides felis felis). Studies have shown that transmission does not occur between cats kept in a flea-free environment. Some ticks may also be able to transmit the disease. Diagnosis in cats is difficult – blood culture is the most reliable means, but it is not always sensitive. Antibody production only confirms exposure but not active infection. Polymerase chain reaction is often faster but no more sensitive than blood culture. An effective treatment regimen to eliminate B. henselae infection in cats has yet to be determined.
Transmission of B. henselae from cats to humans is thought to occur through contamination of scratches and bites (broken skin) with flea dirt (i.e. partially digested blood from the infected animal that is excreted by fleas = flea poop). Infection in individuals with weakened immune systems can be extremely serious or even fatal. In otherwise healthy people, the infection tends to remain localized, but can still cause massive swelling and abscessation of local lymph nodes. The type of disease that occurs may depend on the strain of Bartonella involved.
There are a few simple steps people can take to decrease the risk of cat scratch disease. These are particularly important for individuals with compromised immune systems, in which infection can be much more severe:
- Keep your pets flea- and tick-free. Effective treatment and prevention products are available from your veterinarian.
- Avoid or prevent situations that may result in bites and scratches from your pet. There is more information about this on the Worms & Germs Resources page and in our archives. If you do accidentally get scratched or bitten, be sure to clean the wound thoroughly. Consider seeking medical attention for bites in particular.
- Be aware of where cats come from. Stray or shelter cats less than one year old are most likely to be infected with B. henselae.
It is also important to note that there is NO evidence that declawing cats decreases the risk of transmission of B. henselae to humans!
As a point of interest, Bartonella quintana (a human-adapted Bartonella species) was the cause of trench fever in World War I, and was transmitted by lice.
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)
Neurological bunnies: Encephalitozoon cuniculi
Encephalitozoon spp. are single-celled microsporidian parasites that can cause infection in the intestinal tract of animals and people, and sometimes infection in other parts of the body (systemic infection). Cases of infection with these parasites (encephalitozoonosis) have been reported in countries all over the world. The species E. bieneusi and E. intestinalis are the most common. A much less common species, E. cuniculi, is thought to be one of the most virulent microsporidia that infects humans (i.e. it causes the most severe infections). Encephalitozoonosis is rare in healthy people, but it is a common complication in patients with weakened immune systems. Encephalitozoon cuniculi can also be found in many animal species, particularly in rabbits. Most infections in rabbits do not cause illness (i.e. subclinical infections), but when disease occurs it typically causes neurological signs. In these cases the parasite tends to attack the brain and kidneys. The primary means of transmission between rabbits is E. cuniculi spores shed in the urine. Organ damage in the few human cases that have been reported have also been primarily in the brain and kidneys.
Direct transmission of this parasite from rabbits to humans has not been reported, but because there is also no evidence that it can't be transmitted from rabbits, the disease is so severe when it does occur, and the parasite is so common in rabbits, it is still prudent to take a few simple precautions. This includes washing your hands after handling rabbits, and keeping rabbits away from food preparation areas and food meant for human consumption. Anyone with a weakened immune system should be particularly careful, and ideally should have someone else clean out their rabbit's enclosure on a regular basis.
In general, the risk of illness in a rabbit and zoonotic transmission can be reduced by proper handling, good management, personal hygiene and routine healthcare. A rabbit that is not stressed and is well cared for is less likely to be susceptible to infection, and therefore less likely to transmit infection to a person. More information about rabbits is available on the Worms & Germs Resources page.
Pets and immunocompromised people
There was an interesting article in USA Today about the increasing recognition of the positive role that pets can play in patients recovering from serious disease, and how contact with pets can sometimes conflict with disease transmission concerns in these same patients. The attitude towards pet ownership among physicians is highly variable - some recognize the strong human-animal bond and its positive effects, while others see pets as unnecessary infectious disease risks. The infectious disease concerns are heightened in patients with compromised immune systems, to the point that sometimes people are told to get rid of their pets if they are severely immunocompromised. However, more and more pet owners, veterinarians and physicians are beginning to question if this is truly the best approach.
The USA Today article describes the experiences of a cancer patient whose greyhounds were "banished to a caregiver on doctors’ orders". Considering she was at high risk for (potentially fatal) infectious disease because of chemotherapy, bone marrow transplant, stem cell transplant and immunosuppressive drugs, it’s not surprising that there was concern about the pets. After researching the risks, and measures she could take to reduce those risks, the patient convinced her doctors that the risks from her dogs were not as great as the benefits from having them around, and so the dogs returned home. While everyone’s relationship with their pets is different, the patient felt that the return of her dogs was an important step in her recovery, stating "There's no question that having (the dogs) with me these past few months made a huge difference in my recovery".
Infectious disease transmission from pets to people is certainly a real issue, and it is of particular concern in people with weakened immune systems. There is not, nor will there ever be, a "no-risk" pet. Every contact with a pet, just like every contact with another person, carries with it some degree of risk of disease transmission. What needs to be considered is the trade-off, the risks versus the benefits. In some people, the risks are greater than the benefits because of the severity of disease, type of pet, the person's ability (or more likely inability) to interact with the pet. In other people, especially those who have a very strong bond with the animal, the positive social and emotional benefits of pet ownership may greatly outweigh the associated disease risks. The article contains a great quote from Dr. Ray Pais, a pediatric hematology/oncology specialist, saying "Our young patients have already given up so much, I see no reason at that moment for them to also lose the dog."
People that have compromised immune systems need to have a serious discussion with their physician, veterinarian and family about the best thing to do with their pets while they are sick. While there is very little research in this area, taking a few common sense precautions should reduce the risks of disease transmission. These include:
- Avoiding contact with stool
- Frequent handwashing
- Preventing licking of the person by the pet
- Proper training to reduce the risk of bites and scratches
- Keeping cats indoors
- Following a good preventive medicine program for the pet
More information about Immunocompromised Pet Owners will be available soon on the Worms & Germs Resources page. The CDC also has useful information on its website about this topic.
Thanks to Dr. Doug Powell of Barfblog for forwarding this article.
Nontraditional Pets and Children: Beware
A report about the health risks in children associated with nontraditional pets was recently published in Pediatrics, the official journal of the American Academy of Pediatrics. The report also discusses diseases associated with animals in public settings such as petting zoos and pet stores. Although contact with pets and animals can be beneficial to growth and development in children, it is very important to be aware of the risks associated with certain kinds of animals. Physicians, veterinarians and public health personnel can help parents select appropriate pets in order to maximize the benefits while minimizing the risks to children.
One of the most important pathogens discussed in the report is Salmonella. Although Salmonella can be transmitted by many animal species, including traditional pets like dogs and cats, it is a particularly high risk with certain other kinds of pets, including reptiles, amphibians and baby poultry (chicks and ducklings). It has been estimated that direct or indirect contact with reptiles or amphibians is responsible for 6% of all sporadic Salmonella infections in the US, and 11% of cases among people younger than 21 years. There is also a relatively high risk of Salmonella transmission associated with animal-derived pet treats, such as pig ears, and raw meat.
The report makes several recommendations about how to reduce the risk of infection, injury and allergies from nontraditional pets, many of which you may have seen before on the Worms & Germs website. Just a few of these are:
- Always wash your hands after contact with animals, animal products or their environment, and after contact with animal-derived pet treats.
- Supervise hand washing for children less than five years old
Children less than five years of age and individuals with weakened immune systems should avoid contact with reptiles, amphibians, rodents, ferrets and baby poultry. These animals:
- Should not be kept as pets in households where children less than five years of age or individuals with a weakened immune system live.
- Should not be brought to childcare centres.
- Should not be allowed to roam freely in ANY house or living area.
- Should not be permitted in kitchens or anywhere food is prepared.
More information about Salmonella in pets and the risks associated with feeding raw meat and animal-derived treats to pets can now be found on the Worms & Germs Resources page.
Pet store sued after hamster-associated death
LCMV is a virus that can cause encephalitis and/or meningitis (inflammation of the brain and associated tissues). Human cases are typically associated with rodent contact; both pets and wild rodents. Infected rodents can appear to be healthy. People can be infected through bites or direct contact with rodents, their droppings, urine, bedding or other contaminated materials. Pet-associated infections are rare, and are of greatest risk in people with compromised immune systems, such as transplant recipients, and pregnant women.
Some key points from this report and LCMV in general are:
- All types of pets, even small ones, can transmit infection.
- Sometimes exposure to infectious agents is unavoidable. You’re not going to turn down a donated organ on the rare chance that the donor had an obscure and undiagnosed disease.
- People that are at higher risk for infectious diseases, such as transplant patients, should consult with their physician and veterinarian before obtaining a new pet.
- Appropriate controls should be used to reduce contact of people and pet rodents with wild rodents
- Wash your hands after touching a rodent or its environment
More information about hamsters and lymphocytic choriomeningitis virus is available in the Resources area.
