Overview of Legionnaires’ Disease in Dogs
A client called and asked me a very interesting question: “Can my dog get or give Legionnaires’ Disease?” They were right to be concerned; this disease, unknown to many, can be fatal. A hotel in Philadelphia, PA was the scene of a strange outbreak of pneumonia in 1976 that brought the disease into medical textbooks. A group of American Army veteran legionnaires were the victims; of the over two thousand attendees who had gathered for a meeting that fateful weekend, 220 one were infected, and 34 died. That incident was the first time that the disease-causing organism Legionella pneumophilia was diagnosed, and it remains a relevant problem in healthcare today.
In August 2015, an outbreak in New York infected over one hundred people and killed ten. The sources of the disease have been traced to a mall, a hotel, and a hospital. Given the severity of the disease, this raises a number of questions. What do we know about Legionnaires’ disease? How contagious is it, and can dogs get or transmit it?
According to the World Health Organization, Legionella is a gram-negative, non-spore-forming, rod-shaped aerobic bacteria. There are 42 known species of Legionella bacteria. 1976 was not the first time that Legionella was involved in a disease outbreak. In 1968, a less serious form of the disease infected several people in a department of health office in Pontiac, MI. Caused by a different form of the bacteria, it sickened people with flulike symptoms, but there were no deaths. This version, called Pontiac Disease, has an incubation period of one to three days and tends to affect people in their late 20s to 30s. 90% of those exposed to Pontiac Disease will become ill (potentially as the result of a hypersensitivity rather than an infection). Legionnaire’s Disease, however, has an incubation period of two days to two weeks and is a threat to people 45 and older as well as those with compromised immune systems. It likely accounts for 4% of all pneumonia cases, and it is believed that approximately five out of every 100 exposed people will contract Legionella pneumophilia. It is thought that 8,000 to 18,000 cases are thought to occur in the United States annually. Identifying Legionella must be done by urinalysis, sputum testing, lung biopsy, or blood test.
OSHA reports that Legionella bacteria occur in nature, usually in small amounts. They can be identified in the ground, ponds, lakes, streams, and in other water sources, but the survival of the bacteria requires warm, stagnant water of 90 to 105 degrees F as well as the presence of other bacteria or protozoa and iron, rust, or scale.
Legionella-related diseases are not spread person-to-person, nor animal-to-animal. The bacteria must be inhaled or aspirated to infect a living thing. Colonization of large numbers of the bacteria most commonly occurs in water heaters, cooling towers, and aquatic systems and as aerosolized mist and vapor. Fountains, whirlpools, spas, showers, and other water sources in hotels, cruise ships, railways, nursing homes, and hospitals are all known sources of Legionella infection. People are most likely to contract Legionnaires away from home in commercial settings or while traveling. Potting soils can also harbor the bacteria, and one known outbreak was even caused when the basement of a bar flooded.
Do Dogs Get Legionnaire’s Disease?
There has not been a diagnosed case of Legionnaire’s Disease in dogs or cats. Dogs would be more likely to get a disease known as Leptospirosis from water sources in nature; thankfully, there is a vaccine for Leptospirosis (commonly referred to as “lepto”) to protect household pets. In laboratories, guinea pigs, rats, mice, and marmosets have been purposely infected with Legionella but did not pass it on to other animals in the course of study. Evidence of past infection (confirmed by serum antibody levels) has been discovered in horses and some wild animals, but neither animal reservoir of the bacteria nor transmission between animals has been found. In 1998, one calf died of pneumonia related to Legionella bacteria; the bacteria was found to originate from a hot water system, and no other animals in the herd became ill. It’s safe to say, then, that there is little cause for concern regarding the transmission of the disease via household pets. Given both the rarity of Legionnaire’s disease and the current evidence on the matter, transmission to and from dogs is extremely unlikely and not a cause for concern.
More information on Contagious Diseases of Dogs
There have been several scares about potentially infectious diseases that infect humans. Learn about the impact of dogs on:
Listeria in Dogs (remember the ice cream recalls of 2015?)