Zoonoses or Zoonotic diseases are those that can be transmitted between humans and animals. Salmonella is a zoonosis from pet reptiles that I am asked about on a fairly regular basis, and usually relates to the risk associated with reptile pets and Salmonellosis in humans. Whilst reptiles, amphibians and many other exotic pets can and do transmit Salmonella infection from time to time, sensible hygiene precautions can generally prevent this occurrence. Other precautions are recommended such as refraining from buying wild caught animals which are more likely to be infected, but also may be stressed and debilitated leading to enhanced shedding of infective material. Similarly, buying pet reptiles from clean, professional outlets or breeders may also reduce the risk of acquiring an infected animal in the first place due to decreased chances of transmission between animals where hygiene and cleanliness are scrupulous. Many different Salmonella species and serovars have been isolated from reptiles commonly kept as pets, several of which are infectious to humans.
The difficulty in assessing infection risk from reptile pets lies in the fact that certain Salmonella spp. can be commensal organisms in the gastrointestinal tract of pet reptiles, and also in that they are often intermittently shed so even if screening faecal samples it can be difficult to ensure a pet reptile is Salmonella free. Pets can appear perfectly healthy with no outward signs of infection yet carry a pathogenic strain that could result in severe illness in humans. Transmission to humans is usually via the faecal oral route, and as such any contact with faecal material should be minimised. Hygiene precautions such as washing hands after handling animals, wearing gloves for cleaning reptile housing and for maintenance of aquatic environments and filtration systems are the best defence against infection. Salmonella bacterial cells have been demonstrated to survive and remain infective in the environment for long periods of time, up to 6 months in dried reptile faeces and up to 6 weeks in contaminated aquarium water. Therefore, indirect transmission from the environment to oral ingestion can also be a significant route of infection in homes with reptile pets, particularly where cleanliness and hygiene practices are poor.
Signs of infection in humans include diarrhoea, vomiting, lethargy, abdominal cramps/pain, fever and in severe cases dehydration or even septicaemia and death. The most serious risk for infection is in young children, the elderly and immunocompromised individuals. One of the issues which comes up from time to time in the media, is whether reptiles and amphibians are suitable pets for children in the first place. This debate raged most notably in the 1980’s and early 1990’s when thousands of baby terrapins were being sold to young children in the UK and USA during the teenage mutant ninja turtles craze, resulting in several high profile cases of Salmonellosis in children. Several more recent high profile outbreaks in the USA have linked Salmonella outbreaks in children to aquatic frogs sold for home aquaria.
Transmission can be increased in young children for a variety of reasons, mainly due to not washing hands after handling pets or putting their hands in faecal contaminated water and then touching their mouths. Immunity in young children is also underdeveloped compared with healthy adults so transmission risk is again increased. As such, it is prudent to advise against aquatic pets such as turtles and frogs for young children for safety reasons as much as for the fact that these are specialist pets requiring detailed care and environmental conditions. In a household with very young children that would not understand these precautions, it may be better to limit access to such pets or consider waiting until children are a bit older to allow interaction with them. Similarly, it may be worth re-homing pet reptiles or amphibians if there is a member of the household who is on immunosuppressive medications like steroids or chemotherapy agents, or those with immunocompromising conditions. The alternatives would be rigorous and regular testing to screen for Salmonella spp, recognising that several tests are needs to rule out the disease and also that strict biosecurity will have to ensure infection is not introduced. This could potentially be very difficult to achieve especially considering some outbreaks of pathogenic Salmonella have been traced to rodent or insect food items required for many captive reptile diets.
If keeping reptiles or amphibians in the home with children it is crucial to teach them the importance of good hand washing after handling any animal, not just exotic species. Supervised handling if at all should be encouraged. Cleaning of reptile housing and equipment should never be carried out in areas where food is to be prepared, or drinking water is sourced or even in showers and baths used by the household. Preferably these tasks should be carried out outside the home or in a dedicated sink or washing facility. Cages or tanks housing exotic pets should be cleaned and disinfected with an appropriate disinfectant at the correct concentration on a regular basis. This is especially important for aquatic species who obviously occupy faecal contaminated water and therefore often have a higher potentially pathogenic load of gastrointestinal micro-organisms than other species.
In summary, perhaps reptile and amphibian pets are too great a risk for certain households depending on what practical arrangements can be made to limit risk of infection to vulnerable individuals, particularly young children. It is important to be aware however that with sensible hygiene precautions such pets pose a very low risk and incidence of disease transmission from pets to owners is greatly exaggerated by the media when occasional cases occur. Any signs of gastrointestinal illness in households containing such pets should be investigated by a medical doctor, especially in the vulnerable groups discussed. It is important to also mention that gastroenteritis caused by Campylobacter spp is also sometimes transmitted by captive reptiles and amphibians, and can cause similar signs.