Myasthenia gravis is an immune system disease in which antibodies are produced against receptors in the muscle junction and impair neuromuscular transmission. It is characterized by episodic weakness associated with exercise. A dog's stride may be shortened, followed by collapse in the hind legs, or all four limbs. Paresis (a disturbance in the mechanism for initiating voluntary motor function) may involve facial nerves as well as spinal nerves. Inability to blink both eyes is most commonly observed along with generalized muscle weakness. Additionally, there may be a change in bark, respiratory difficulty, and vomiting The vomiting is due to a megaesophagus. Myasthenia gravis can be either congenital or acquired. Springer spaniels, Jack Russell terriers, and Fox terriers have been reported to have the congenital form. Several cases have been diagnosed in Hungarian vizslas. Diagnosis is made through the use of a test dose of a medicine called edrophonium chloride given intravenously. An immediate short-lived (3-8 minute) response is observed. Long-term treatment involves corticosteroids.
The immune system is trained, in early life, not to recognize the body's own proteins as self. The current thinking regarding the factors that can make the body stop recognizing its own proteins as self is that the multiple autoantibodies seen in man (even in the absence of disease) may stem not from some inherent malfunction of the immune system itself, but from antibodies raised to the numerous pathogens that humans and animals randomly encounter during the course of their lifetime. In this way, pathogens might be able to influence disease processes, even when no longer present. Moreover, pathogen proteins closely resemble our own, and that immune attack directed towards the pathogen may thus result in antibody cross-reactivity with human proteins. Hence, autoimmune diseases can be pathogen-associated and such agents may be able to punch far above their weight and influence biological processes even after their successful removal. For example, Toxoplasma gondii is not only implicated in schizophrenia and related disorders, but also in Alzheimer's or Parkinson's disease, cancer, cardiac myopathies, and autoimmune disorders. If toxoplasmosis in cats and other pets was registered as a notifiable disease requiring obligatory treatment by veterinarians, perhaps the incidence of several diseases, including autoimmune, could be reduced.