According to the American Heartworm Society, The Western Journal of Medicine and Surgery of 1847 makes first mention of heartworm in dogs of the United States. Heartworm was discovered in cats later in the 1920s. This disease is a subtle but deadly threat to dogs, cats, other mammals such as foxes, wolves and ferrets. On very rare occasions, a human can be infected with heartworm, but it so seldom occurs that it is not considered a public health threat.