Vaccines are designed to protect dogs against specific diseases by stimulating the immune system to attack and kill the infectious agents causing them. In rare cases, though, vaccines can either bring on the disease itself or produce symptoms that mimic it so closely that the real and the vaccine-induced diseases are indistinguishable. Some, including the most dreaded one of all, rabies, attack the dog's central nervous system. No centralized reporting system to track such extreme reactions exists, so the frequency is unknown, but adverse reactions to vaccines, often with neurological symptoms, are common enough to have generated considerable controversy within the field of veterinary medicine over when (or whether) the potential benefits of some vaccines outweigh the risks.
Lyme Vaccine Disease
Lyme vaccine disease mimics the symptoms of Lyme disease, a serious bacterial illness transmitted to dogs through the saliva of infected deer ticks, including high fever, loss of appetite, swollen lymph nodes, joint inflammation and sometimes neurological disorders. Although vaccines exist, they are controversial because they may not prevent reinfection, and many complications from reactions have been reported, including seizures, neuropathy (nervous system damage) and cognitive impairment.
Rabies Vaccine-Induced Encephalitis
Also called vaccine-induced rabies, this deadly disease is rare but when it occurs symptoms start to show up 10 to 21 days after vaccination and are identical to rabies, including limpness, paralysis and severe inflammation of the dog's brain and spinal cord. As with rabies, symptoms may vary depending on which part of the nervous system is under attack. Like many other vaccines, rabies vaccines fall into two general categories: "modified live" (weakened) or "killed." In susceptible dogs, modified-live vaccines have the potential to become active and cause diseases, including vaccine-induced rabies. Killed vaccines, on the other hand, can't cause disease but are more likely to trigger serious allergic reactions. The only difference between rabies and vaccine-induced rabies is that the sick animal is not infectious to others but the condition is incurable and terminal.
Also called polyradiculoneuritis, Coonhound paralysis is another disease that can affect dogs following injection of modified-live rabies vaccine. Since the autoimmune system attacks the nerves supplying the muscles, symptoms include flaccid paralysis (floppy dog syndrome), leaving the dog completely paralyzed to the point that it might become unable to breathe on its own. With intensive care, some dogs survive this disease but the recovery takes months and is very expensive.
Postvaccinal Canine Distemper Virus Encephalitis
Canine distemper, a highly contagious viral disease, is the most common cause of brain inflammation (encephalitis, also called encephalomyelitis) in dogs and the modified-live canine distemper vaccine has frequently been implicated in adverse reactions of various kinds. Canine distemper virus encephalitis is the most serious, with symptoms the same as the disease itself, including seizures, lack of coordination, behavioral changes and cognitive impairment.
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