Effect of gamma-irradiated commercial dry pet food in cats
From Felipedia
Similar to an outbreak of food-related fanconi-like symptoms in dogs caused by Veggie Dent™ Chews For Dogs (Virbac) in June 2009, a similar food-related outbreak of disease occurred betweeen June 2008 and March 2009, where 87 cats in Australia developed symmetrical hindlimb ataxia, paraparesis, tetraparesis, paraplegia or tetraplegia. The affected cats ranged in age from 10 months to 15 years and all were either indoor/outdoor domestic pets. In total, 69 affected cats came from Sydney and the remainder were reported from Newcastle, Melbourne, Canberra and Adelaide. Sixty four of these cats were examined by one or more of the authors, a further 10 were reported by other veterinarians and 13 cats were reported by authors by their owners[1].
Both male and female cats were affected and all except two were neutered; 40 were Domestic shorthair, with other represented breeds including Domestic longhair, Burmese, Siamese, Himalayan type, Maine coon, Cornish rex, Devon rex and Bengal. In households with more than one cat, multiple cats were affected, but the severity of clinical signs varied among them.
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Cause
The majority (85/87) of cats were reported to have eaten Orijen (Champion Petfoods Ltd, Canada) dry cat food in the months preceding the onset of neurological signs. Two cats ate only Orijen dry dog food. In households where cats were affected after eating Orijen dog food, dogs in the household have not shown any neurological abnormalities to date. More than half of the affected cats were fed other food in addition to Orijen during the same period, but some cats were fed the dry food exclusively and others were fed Orijen as a small part of their daily diet. Additional foods included other commercially available canned and/or dry foods, and raw or cooked meat. No single food product, except Orijen dry food, was fred to all affected cats. The period of time that Orijen was fed to the affected cats ranged from less than 1 month to 10 months. The total amount of Orijen fed has not been correlated with the severity of clinical signs. The onset of clinical signs in all cats was at least 2.5 to >6 months after the food was first fed. Onset of clinical signs was seen in some cats that had not been fed Orijen for more than 2 months. No other cats have been seen in this period of time that had similar clinical signs that have not been fed Orijen dry food.
No metabolic cause has been established in the affected cats. Nutritional deficiency is considered unlikely since most cats were also fed other foods and deficiency in the Orijen food has not been established. Single dose gamma irradiation is suspected of causing some changes to volatile fatty acids or producing oxygen radicals which affect detrimentally on neuronal lipid membranes.
Melamine toxicosis has been reported in cats, but was not present in this commercial food.
Clinical signs
The initial presenting abnormalities have included difficulty in jumping, landing heavily and with a sewaying, often wide-based, crouching hindlimb gait. Symmetrical hiundlimb paresis and ataxia progressed in more than 50 of the affected cats, to non-ambulatory severe paraparesis or paraplegia, and in 13 cases to tetraparesis or tetraplegia over a period of 4 to 8 weeks. Curently the worst affected cats have shown tetraparesis and either spastic paraplegia or tetraplegia.
The neurological abnormalitites are indicative of an upper motor neurone abnormality with decreased or absent postural reactions in affected limbs, normal to increased spinal reflexes and normal to markedly increased muscle tone, No significant muscle atrophy has been seen unless the cat was paralysed and recumbent for extended periods. Spinal pain was reported initially in two cats, but has not been a typical feature. Several owners have commented that twitching or involuntary spasms occurred in either the hind- or forelimbs, especially when the cats was attempting to eat or urinate or defecate, and some cats paraplegic or tetraplegic cats have developed urinary incontinence. The most severely affected cats showed a subtle head tremor and/or difficulty eating, but all have remained seemingly alert adn responsive to their owners. The menace reponse was absent in less than 10 affected cats and several of them have shown vision abnormalitites. Many owners reported that their cat's behaviour changed, with the cat seeming to be more quiet or subdued than previously.
Affected cats have had diferent evaluations, but in those tested, no abnormalitites have been found on complete blood count, biochemistry profile, serologic testing (FeLV, FIV, Toxoplasma gondii, Cryptococcus spp), serum cholinesterase activity, blood lead determiantion, spinal radiography, CSF analysis or muscle biopsy.
Postmortem examination was carried out in seven cats. No gross abnormalitites were found. Histopathological abnormalities were confined to the nervous system in six cats, characterised by severe diffuse leucoencephalopathy. One cat also showed renal amyloidosis. Degenerative changes were seen diffusely throughout the spinal cord, affecting the white matter of predominantly the lateral and ventral funiculi with moderate to severe spongiform vacuolation, occasional large swollen axons, prominent blood vessels and rare, occasional perivascular mononuclear cuffing. Similar but less severe changes were also noted in the brainstem. Mild spongiform degeneration was present in the cerebellar white matter in some cases. Other causes of spongiform encephalopathy were excluded.
Treatment
Treatment given to affected cats consisted of a change to another nutritionally balanced diet, nursing care and physiotherapy. No significant difference in the rate or degree of improvement in neurological function was seen with treatment wit vitamin and antioxidant supplements (including vitamins A, E, C, B and glutathione), minerals (e.g. copper and potassiumk), omega 3 fatty acids or empirical treatment with antibiotics, including clindamycin and/or prednisolone compared with nursing care and a change in diet only.
It is suggested by authors that food irradiation at high levels (>36.3 kGy) is associated with the development of leucoencephalopathy in cats and should be avoided.
Reference
- ↑ Child, G et al (2009) Ataxia and paralysis in cats in Australia associated with exposure to an imported gamma-irradiated commercial dry pet food. AVJ 87(9): 349-350
