Mushroom toxicosis: cause or confounder in seasonal canine illness?


In the case report published in this edition of JSAP, Hall & Barton (2013) describe mushroom toxicosis in dogs that were admitted to an East-Midlands out-of-hours veterinary practice. The authors suggest that mushroom toxicosis is uncommon, but that this may be due, in part, to under-diagnosis by veterinary practitioners who may not recognize the clinical signs. The article plays an important role in raising awareness of the clinical signs associated with mushroom toxicosis in dogs, which the authors hope will improve the recording of clinical information in future cases. They also suggest that mushroom toxicosis could be a differential diagnosis for some cases of seasonal canine illness (SCI), because of the similarity in clinical signs and epidemiology between the two syndromes.

SCI is a condition of as yet unknown aetiology, characterized by clinical signs that most commonly include vomiting, diarrhoea and lethargy. It is consistently seen in conjunction with a recent exposure to a woodland environment, invariably in the autumn. The Animal Health Trust (AHT) has been investigating SCI since 2010, when it was first made aware of an emerging syndrome affecting dogs walked in woods on the Sandringham Estate in Norfolk. The AHT quickly established a means, using an owner-completed questionnaire, to collect information from affected and non-affected dogs walked at several sites in East Anglia and Nottinghamshire that were all reporting the occurrence of a similar syndrome among dogs walked in their woodlands around the same time of year. Although the aetiology of SCI remains to be elucidated, the AHT has made progress with its research into the syndrome and a summary of progress to date has been submitted recently for publication, which concentrates on the epidemiology and spatial analysis of dogs walked at the Sandringham Estate.

Looking to the future, the AHT hopes to use novel pathogen/agent discovery techniques on samples that have been collected and archived since the beginning of the investigation in 2010. However, a legitimate criticism and hindrance to progress in any investigations into SCI is that it is not currently possible to make a definitive diagnosis of SCI, as the case definition is based on non-specific clinical signs that are relatively common in dogs and the aetiology remains unknown. Previously published frequency estimates of owner-reported cases of gastrointestinal disease in dogs have been as high as 18·9% for vomiting and 14·9% for diarrhoea (Hubbard et al. 2007). Reliance on such a generic case definition provides opportunity for misclassification of SCI cases and it is possible that some cases that have been reported to the AHT as presumed SCI may in fact be due to mushroom toxicosis, as reported by Hall & Barton (2013). However, SCI field investigations at Sandringham have revealed no evidence of an abundance of toxic mushrooms that would explain the temporal and spatial clustering of cases in the area. In September 2010, there was a peak of 4 cases reported in a single day, and 17 cases in total for that month. In 2011, there was a peak of 7 cases reported in a single day, and a total of 34 cases reported throughout September. Mushroom toxicosis in dogs as recognized by Hall & Barton (2013) is rare, therefore, for similar temporal and spatial clustering of cases would need an abundance of mushrooms in the same geographical area to allow a large number of dogs to come into contact, and subsequently ingest the mushrooms. There are also some differences in reported clinical signs between the two syndromes, such as ptyalism, which was reported consistently with the mushroom toxicosis cases reviewed by Hall & Barton (2013) but has not been reported to the AHT as a clinical sign of SCI. Also, review of postmortem data from four suspect SCI cases investigated by the AHT indicated that there was no hepatic necrosis identified which is common with mushroom toxicosis, particularly with the Amanita genus (Liggett & Weiss 1989, Puschner et al. 2007).

Syndromic surveillance systems that use data collated from veterinary practice management systems (PMS) have the ability to provide vital data on the prevalence, temporal trends, spatial distribution and risk factors for disease, and may be specifically valuable for diseases with low frequency or prevalence estimates, such as mushroom toxicosis. These systems might also be used to assist in the identification of emerging diseases, such as SCI, and provide information to aid the establishment of early warning systems and control methods. The importance of such scanning syndromic surveillance in detecting emerging syndromes and new infections was recently illustrated with the identification in Europe in 2011 of a novel disease syndrome in ruminants due to infection with Schmallenberg virus (SBV), although in SBV the clinical syndrome is fairly clearly defined by congenital abnormalities among infected offspring. In turn, heightened awareness and adoption of appropriate agent detection diagnostic methods led to the early confirmation of the disease in the UK in 2012. The need also for collation of these types of data for dogs was highlighted in Professor Sir Patrick Bateson's report on his “Independent Inquiry into Dog Breeding”, published in 2010. It was specifically noted there was a need to “collect data from a broad spectrum of veterinary practices, referral practices, University veterinary hospitals and other small animal clinics”, (Bateson 2010). In this case, it was to guide the development of strategies to breed away from specific disorders and provide evidence for future regulations on dog breeding, but might equally apply in better describing emerging syndromes.

Retrospective evaluation of veterinary clinical records for evidence of seasonal patterns of canine gastrointestinal-manifested disease which predate the recognition of SCI in 2010 may identify previously unrecognized clusters of SCI. This type of analysis could help identify whether SCI was likely to have existed as an unrecognized syndrome previously in areas where it was subsequently identified, providing further data and information on which to refine on-going investigations. Syndromic surveillance methods might also assist with SCI case reporting. Current investigations mainly rely on owner reported cases, resulting in information received from dog owners regarding affected (case) and non-affected (control) dogs, which are both necessary in epidemiological case–control studies. However, to improve the case definition, veterinary attended cases would provide more reliable and detailed clinical and pathological data. Using a system such as SAVSNET (Radford et al. 2010), where data are collected directly via veterinary PMS, would enable practices to report possible cases, with minimal additional effort required from the veterinary surgeon. The clinical information could be coupled with the additional information on time of year (taken automatically from the date of consultation) and recent possible exposure to woodland environments, which could be specifically sought through questions prompted from within the PMS. This method of prospective disease surveillance has been developed in project 2 of the SAVSNET initiative which encompasses electronic data retrieval from veterinary practitioners who record data at the end of each consultation via their VetSolutions clinical software in order to obtain real-time syndromic surveillance data. The system has been successfully piloted over three phases and has demonstrated its ability to collate and collect data from multiple, geographically diverse practices simultaneously and to increasingly deal with a range of syndromes, including antibacterial prescribing patterns (Radford et al. 2011). Similarly, VetCompass, developed by the Royal Veterinary College, links data stored within PMS to a diagnosis made at the time of consultation, thereby allowing disease and treatment to be monitored consistently over a wide area as well as over time (Kearsley-Fleet et al. 2013). VetCompass uses a form of veterinary medicine nomenclature coding (known as the VeNom codes) to standardize the recording of clinical data within the PMS, which aids the standardization of diagnoses made across different practices, by different individuals at different times.

With the help of new syndromic surveillance systems such as SAVSNET and VetCompass, increasing awareness of emerging syndromes amongst first opinion veterinary practitioners, and on-going and future targeted investigations such as those undertaken by the AHT and Hall & Barton (2013), we are hopeful that specific aetiologies of SCI can be identified and preventive measures taken to reduce the number of animals affected.

Richard Newton joined the Epidemiology Unit of the Animal Health Trust in 1994 after graduating in Veterinary Science from Liverpool University in 1991 and working in mixed practice. Since completing a Masters in Communicable Disease Epidemiology at the London School of Hygiene and Tropical Medicine in November 1998 he has worked on the epidemiology of a variety of diseases of companion animals, including grass sickness, EIPH and strangles in horses and influenza, including cross-species transmission from horses to dogs. He completed his PhD on the epidemiology of equine infectious respiratory disease in 2002 and in 2003 was awarded both the Diploma of Fellowship from the Royal College Veterinary Surgeons and became a de facto Diplomate of the European College of Veterinary Public Health. He is currently Head of Epidemiology and Disease Surveillance at the Animal Health Trust. The group at the AHT currently has programmes on infectious disease surveillance in the UK for which it prepares quarterly disease reports for Defra. He also oversees dedicated programmes on grass sickness surveillance and vaccination and investigation of “seasonal canine illness”, an emerging disease syndrome in dogs walked in woodland environments in the autumn months.

Charlotte Robin graduated from the University of Central Lancashire with a BSc in Equine Science and an MRes in Equine Biomechanics. She started working at the Animal Health Trust as a Research Assistant in the Epidemiology and Disease Surveillance department in 2010, and is currently the seasonal canine illness Research Co-ordinator.