I’ve written about the African dwarf frog and Salmonella issue before, but it’s worth a recap since an overview of the 2008-2011 outbreak was recently published in the journal Pediatrics (Mettee Zarecki et al 2013). The fact that reptiles and amphibians can carry Salmonella is nothing new, nor is the fact that outbreaks of disease can occur in people who have contact with them. However, the scale of outbreaks associated with pets can be impressive.

Here are some highlights from the paper:

  • Between January 1, 2008 and December 31, 2011, 376 people were diagnosed with salmonellosis caused by the outbreak strain, a type of Salmonella Typhimurium.
  • As is common in pet-associated outbreaks, kids bore the brunt of this one. The mean age of infected individuals was 5 years, and 69% were children under the age of 10.
  • Severe disease wasn’t uncommon – 29% of people were hospitalized, half of those being kids less than 5 years of age. Fortunately, no one died.
  • During a preliminary study, when they compared people who got sick with a group of healthy controls, they found that people who reported exposure to any aquatic pet were almost 5 times as likely to have salmonellosis. When that was narrowed down to exposure to just frogs, the risk went up to 12.4 times higher than healthy controls.
  • When they looked at people who were sick and reported exposure to frogs, only 27% reported having touched a frog, with 46% reporting having fed a frog, 59% having had contact with a frog’s habitat and 60% having had contact with water from a frog’s habitat. Twenty-three percent (23%) reported cleaning the frog’s habitat in the kitchen sink, and 35% in the bathroom sink. This tells us some very important information. It tells us that direct contact with frogs or their environment is a high risk behaviour. However, direct contact isn’t required to get sick. While the frog may stay in its habitat, Salmonella may not. Cleaning habitats in kitchen or bathroom sinks is a high risk activity, because it can result in contamination of common human-touch surfaces and items that go into peoples’ mouths (e.g. toothbrushes, cups).
  • Often, disease occurred not long after a new frog was obtained. The median time from purchase of a frog to disease was 30 days (range 5-2310 days).
  • Only 17% of people interviewed reported knowing that frogs can carry Salmonella. Over twice as many knew there was a risk from reptiles. This shows there needs to be more education of people who buy animals such as frogs. Pet stores should be required to provide some basic public health information. Pet owners should also take initiative and research potential new pets, including how to care for them and how to reduce the risk of zoonotic infection.
  • The outbreak Salmonella strain was found in the environment of some patient homes (not surprisingly), an African dwarf frog vendor (potential source of infection), a large-scale African dwarf frog distributor (a great way to spread an outbreak across the continent) and a daycare centre (that never should have had an amphibian in the first place!).
  • One breeding facility in California was the likely source. With centralized, large-scale breeding and warehouse-style distribution of pets (of various species, not just frogs), we’re seeing more large-scale outbreaks like this.

More information about African dwarf frogs can be found on the Worms & Germs Resources – Pets page.