2019 AAFP Feline Zoonoses Guidelines

Dear Editors, – We read with much interest the recent ‘2019 AAFP Feline Zoonoses Guidelines’ published in the Journal of Feline Medicine and Surgery. ¹ There is no doubt that this article provides valuable information about feline zoonotic diseases to owners, physicians, veterinarians and feline shelter staff to allow logical decisions to be made concerning cat ownership, ¹ and we congratulate the authors for this publication. However, some other important feline enteric zoonoses were overlooked. Therefore, we offer the following comments in relation to the 2019 AAFP Feline Zoonoses Guidelines.

For a long time, microsporidia, a diverse group of obligate eukaryotic intracellular parasites formerly classified as Protozoa and recently accepted into the Fungi kingdom, have been recognised to infect a wide variety of vertebrate and invertebrate hosts. ² Enterocytozoon bieneusi and Encephalitozoon species are the major microsporidian species infecting human beings. ² Of these, zoonotic E bieneusi, the most human-infective microsporidian species, and Enterocytozoon intestinalis have been identified in cats.^3–11 E bieneusi colonises the epithelium of the small intestine and localises predominantly within the apical villus. ¹² Healthy individuals generally have self-limiting diarrhoea when exposed and, following oral intake of mature microsporidia, spores are shed in the host’s faeces and transmitted through human-to-human, animal-to-human, water-borne and food-borne contamination.^13,14 In contrast, life-threatening chronic diarrhoea can develop in immunocompromised patients suffering from acquired immune deficiency syndrome, organ and bone marrow transplant recipients, patients with diabetes, Crohn’s and malignant disease, cancer patients undergoing chemotherapy, travellers, elderly individuals and even children.^15,16

In earlier studies we found that even asymptomatic indoor cats may be positive for E bieneusi genotypes D and IV, which are categorised as group 1 genotypes that generally have broad host and geographic ranges with zoonotic importance (D, EbpC, type IV, etc).^2,17 We also submitted to GenBank a valid internal subscribed spacer (ITS) sequence for E bieneusi genotype IV (accession number MG727664), the first time this has been found in a domestic cat host in the Western Palearctic region. ⁸ Similarly, using molecular techniques, E intestinalis (accession number MG570080) was found in asymptomatic indoor cats and a valid ITS sequence was submitted to GenBank; again representing the first time this pathogen has been recognised in domestic cat hosts worldwide. ⁸

In conclusion, microsporidia remain listed as a category B pathogen, which is the second highest priority category for organisms/biological agents in the National Institute of Allergy and Infectious Diseases (NIAID) pathogen priority list for emerging infectious diseases/pathogens. ¹⁸ The human–animal bond is an umbrella term applied to the kinds of social attachments that typically develop between people and their pets. ¹⁹ Cats are perceived to be valued as companions, especially by elderly individuals. For this reason, cats could play an important role in the transmission of zoonotic microsporidia, potentially representing reservoir hosts that are able to transmit E bieneusi and E intestinalis to humans.^3–11

Therefore, we strongly suggest that the zoonotic microsporidian species, especially E bieneusi genotypes categorised under group 1 and E intestinalis, should be added to the list of enteric feline zoonoses in the 2019 AAFP Feline Zoonoses Guidelines to support the international One Health movement.

Dr Michael Lappin, chair of the AAFP Zoonoses Guidelines Panel, responds:

The Panel thanks the authors for a well-crafted letter concerning the zoonotic microsporidia, with emphasis on Enterocytozoon species. We are sure the references provided will be of benefit to the readers of the Journal of Feline Medicine and Surgery and we are pleased to see the letter published. We agree that these agents are well recognized as having a wide host range and should be considered zoonotic agents.

At the time of writing these American-based guidelines, the Panel did not find published evidence for direct transmission of Enterocytozoon species from infected cats to humans in the US and so did not include the agents specifically in Table 1 or in the discussion. Since there are hundreds of zoonotic diseases, we had to focus on those most commonly encountered by small animal practitioners and physicians, and were not able to focus specifically on all enteric agents that could be shared between cats and humans. However, we believe that if veterinarians and cat owners follow the general guidance for ‘Lessening the risk of zoonotic transfer of disease from cats’ listed in the 2019 AAFP Feline Zoonoses Guidelines, risk of exposure to zoonotic microsporidia will also be reduced.