Prevention key to help protect patients from zoonotic diseases

During warmer weather, when exposure to both wild and domesticated animals potentially increases, sharing the latest information on animal-borne diseases and reminding patients and their families of simple preventive measures can help keep them safe, according to experts.

“Just about every animal has the potential to spread disease, either directly or indirectly, through their secretions and excretions,” said James H. Brien, DO, vice chair of education, pediatric infectious disease, Texas A&M Health Science Center College of Medicine. “From a common sense standpoint, it would seem good advice to avoid animals of unknown background, but it’s also common sense to allow children to learn the many lessons that pets can teach. Whatever species the pet happens to be, it just needs to be healthy, properly immunized, clean and without fleas, as verified by a veterinarian.”

Infection risks from animals in public settings

Data collected by the CDC indicated that between 1996 and 2010, there were approximately 150 human infectious disease outbreaks related to animals in public settings such as petting zoos, farm fairs, nature parks, educational exhibits, childcare facilities and others. Animals, both wild and domestic, that are infected with enteric bacteria and parasites pose the most risk to humans in these settings.

Escherichia coli O157:H7 and other Shiga toxin-producing E. coli (STEC) — Salmonella enteric, Cryptosporidium species and Campylobacter — are the most common pathogens responsible for outbreaks, according to “Compendium of Measures to Prevent Disease Associated with Animals in Public Settings, 2011,” a recent National Association of State Public Health Veterinarians Inc., (NASPHV) report published by the CDC.

The primary mode of transmission is fecal-oral, meaning that people are at risk when they pet, touch, feed or are licked by animals because they can harbor fecal organisms in their fur, hair, skin and saliva. “Unless the animals have been cleared by a veterinarian of any infectious disease, much like the animals used in children’s hospital wards, I would not advise this sort of contact, especially if the child has any immune deficiency,” Brien said. “If contact cannot be avoided, then of course, common sense hygiene measures should be practiced, like thorough hand washing.”

Although livestock are often implicated in outbreaks, amphibians and reptiles are also increasingly associated with infection, particularly salmonella. “Health care practitioners and public health officials should ask specifically about reptile and amphibian exposure among persons with salmonellosis,” researchers wrote in a 2004 Clinical Infectious Diseases study that examined human salmonella outbreaks in the US.

In April, the CDC issued a warning to parents of children aged 5 years or younger, or those with compromised immune systems, to avoid contact with “water frogs and their habitats.” The alert came after a 2-year investigation into more than 200 reports of S. typhimurium from 41 states that led officials to a water frog breeder in California. The infections were all associated with African dwarf frogs and the water from their tanks and aquariums.

Recommendations from the 2004 study included not keeping reptiles and amphibians in childcare centers and not allowing children aged 5 years or younger or children with compromised immune systems to touch these species. “Always wash hands with soap and water after handling reptiles and amphibians or their cages,” the researchers wrote.

Hazardous animal bites and scratches

Children aged 5 to 9 years are most at risk for dog bite injuries, according to statistics posted on the CDC website. Most dog bite injuries (64.9%) among children aged 4 years or younger were to the head/neck region, according to a study published in a 2001 issue of Morbidity and Mortality Weekly Report.

“It is important that physicians now include the concept of pet ownership in their interviews, as pets are present in more than one of two households in the USA and many European countries,” Bruno B. Chomel, DVM, PhD, professor of zoonoses at the School of Veterinary Medicine at the University of California, Davis, told Infectious Diseases in Children. “It should be written in the patient record, as well as which pets the patient’s own, such as dogs, cats, reptiles or birds.”

Among the bacterial pathogens most associated with bites and scratches from pets, according to Chomel and the CDC, are Pasteurella species, which can lead to meningitis and encephalitis; Bartonella henselae (cat-scratch disease), which can cause fever, fatigue and headache; and Capnocytophaga canimorsus, which can cause sepsis. In the case of pet monkeys, particularly macaques, simian herpes B virus can lead to fatal meningoencephalitis.

“Sharing our [homes with pets] may be a source of psychological comfort, but because pets can bring a wide range of zoonotic pathogens into our environment, sharing is also associated with risks,” Chomel and Ben Sun, DVM, MPVM, of the California Department of Public Health, wrote in a recent issue of Emerging Infectious Diseases. Although uncommon with healthy pets, according to Chomel and Sun, “transmission of zoonotic agents by close contact between pets and their owners by close contact with their owners through bed sharing, kissing or licking is real and has even been documented for life-threatening infections such as plague.”

“And don’t forget about rabies,” Chomel said in an email. Globally, the most common source of rabies transmission is through bites from rabid dogs. As of 2009, in the US, wild animals accounted for 92% of reported rabies cases, according to the CDC; domesticated animals — mostly stray cats — accounted for approximately 7%. Raccoons, bats, skunks and foxes are the prime carriers in the US; in Puerto Rico, it is the mongoose.

Parasites such as Sarcoptes scabiei, a skin mite often carried by dogs, cats and cattle, are another hazard of animal contact. “Although human infestation from animal sources is usually self-limiting, skin irritation and itching might occur for multiple days and can be difficult to diagnose,” according to the NASPHV report.

Prion diseases

Proteinaceous infectious particles (prion diseases) such as bovine spongiform encephalopathy (mad cow disease), variant Creutzfeldt-Jakob disease and chronic wasting disease (CWD) are rare but important to recognize. “While prion diseases are rare, they are generally fatal for anyone who becomes infected,” Joseph Y. Abrams, MPH, of the CDC’s National Center for Emerging and Zoonotic Infectious Diseases, said in a press release. “Since chronic wasting disease in deer and elk is likely spreading in geographic range, this could be considered an ongoing outbreak; however, transmission of chronic wasting disease has not been detected in humans.”

Abrams and colleagues said in a recent issue of the Journal of the American Dietetic Association that CWD-endemic areas in the US include northeastern Colorado, southeastern Wyoming and southwestern Nebraska. “Hunting and consuming elk or deer could put people into contact with chronic wasting disease particles,” Abrams told Infectious Diseases in Children.

If patients and their families engage in hunting, Abrams said the CDC recommends checking with state wildlife agencies to identify areas where CWD occurs.

“In these areas, simple precautions can help protect hunters from potential exposure,” he said. “Hunters should avoid eating meat from deer or elk that appear to be sick. Before consuming the meat, consider having the animal tested. Information about testing is available from most wildlife agencies. Hunters should also avoid handling or eating brain or spinal cord tissues from any deer or elk. Those involved in field dressing carcasses should wear gloves and bone-out the meat from the animal.” – by Whitney McKnight

Abrams JY. J Am Diet Assoc. 2011;111:858-863.

CDC. Campylobacter. Available at: www.cdc.gov/nczved/divisions/dfbmd/diseases/campylobacter/. Accessed June 7, 2011.

CDC. Cat-scratch disease. Available at: www.cdc.gov/healthypets/diseases/catscratch.htm. Accessed June 7, 2011.

CDC. Dog bite prevention. Available at: www.cdc.gov/HomeandRecreationalSafety/Dog-Bites/biteprevention.html. Accessed May 27, 2011.

CDC. Investigation update: Outbreak of human Salmonella typhimurium infections associated with African dwarf frogs. Available at: www.cdc.gov/salmonella/water-frogs-0411/042711/index.html#investigation. Accessed May 27, 2011.

CDC. Rabies. Available at: www.cdc.gov/rabies/prevention/people.html. Accessed May 27, 2011.

CDC. Wild animals. Available at: www.cdc.gov/rabies/location/usa/surveillance/wild_animals.html. Accessed May 27, 2011.

Chomel BB. Emerg Infect Dis. 2011;17:167-172.

Mermin J. Clin Infect Dis. 2004;38(Suppl 3):S253-261.

NASPHV. MMWR Recomm Report. 2011;60(RR-04):1-24.

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