MICROCHIPS: CONSIDERING ADVERSE REACTION RISKS, IMPLICATIONS FOR LEGISLATED MANDATES

Microchip identification of animals with injectable, permanent implants readable by widely available scanners is now the most common method of identification of domestic animals and largely effective when individual data is registered with an accessible national database.  But is it medically safe? 

Injecting any foreign substances into tissue carries a risk of adverse reaction. In the early 1990’s cat rabies vacination became a political issue associated with controlling cat population and owners.  We argued that cat rabies vaccination carried a risk of fibrosarcoma, a malignant cancer, at the injection site and should be based on the individual animal’s risk factors in consulation with its veterinarian.  While the incidence of rabies in cats varies geographically, the incidence is nearly nil in California so that indoor only cats are at very low risk of exposure.  Back then, our arguments were ignored by lawmakers, but the incidence of the deadly cancer rapidly increased as more cats were vaccinated and the financial and emotional toll on owners skyrocketed.  Veterinarians, facing liability and ethical practice issues began to take problem seriously. 

In 1996 the Vaccine-Associated Feline Sarcoma Task Force was established, funding an exponential number of studies, developing guidelines for diagnosis and management of sarcomas and vaccination.  Like cat licensing and rabies vaccination, microchipping is increasingly seen as a law enforcement tool for mandated use in the general population of cats and dogs regardless of individual identification needs. 

A recent article in Veterinary Pathology, cite as Vet Pathol 43:545-548 (2006) reports a 2004 case of a 9 year old French Bulldog presenting with a sudden growth of a subcutaneous mass.  The mass was surgically excised with a microchip attached to is.  The mass was a high-grade infiltrative fibrosarcoma.  The authors conclude that “…reports on adverse reactions to vaccination and micchips are strongly encouraged to deepen the current knowledge on their possible role in tumorigensis.”  A free abstract of the article is available, and the entire article is available for a charge of $8.00. 

Mandated use of microchips, even multiple microchips implanted in individuals, in mass populations of privately owned pets will likely increase the reports of adverse reactions before the medical implications are fully understood. 

February 2, 2007

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