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Dogs shake for a variety of reasons, some of which indicate a physical or emotional state of being, and some of which indicate a veterinary emergency. Shaking or shivering should not be confused with seizures, which are sudden neurological events that cause involuntary muscle movements and may result in your dog becoming unresponsive.

Named after Thomas Addison, the Scottish physician who first described the disease in humans, Addison’s disease (more correctly known as hypoadrenocorticism) occurs when there is an underproduction of the steroid hormones by the adrenal glands. The most common cause of canine hypoadrenocorticism is the destruction of the adrenal glands by the pet’s own immune system, although adrenal gland tumors or certain medications can also result in steroid hormone deficiency. Hypoadrenocorticism is extremely rare in cats and is less well characterized than the disease is in dogs. In a normal dog or cat, the two major steroid hormones produced by the adrenal gland are cortisol and aldosterone. Cortisol is a stress hormone that regulates metabolism and the production of glucose. A deficiency in cortisol can result in low blood sugar. The hormone aldosterone regulates the body’s electrolytes, specifically the levels of potassium and sodium in the blood, both of which are important for normal nerve and muscle function. Aldosterone deficiency causes potassium to build up in the blood which, in severe cases, can lead to an irregular heartbeat or stop the heart entirely. The atypical form of hypoadrenocorticism occurs when there is only a deficiency in cortisol while aldosterone levels remain normal.

Zoonotic diseases or zoonoses are diseases that can be passed from animals to humans. Zoonoses are caused by microorganisms such as bacteria, viruses, parasites, or fungi. These microbes spread between animals and people in the following ways: Direct contact – spread directly through immediate contact with an infected animal, including its saliva, blood, urine, mucus, and feces. Infections can spread through a direct touch, bite, or scratch. Indirect contact – spread indirectly through contact with contaminated areas or objects, such as soil infected by an animal’s feces or a pet’s food dish contaminated by bacteria. Vector-borne – spread through a “middleman” that carries the disease from animals to people. Common vectors that spread disease between people and pets include fleas, ticks, and mosquitos. Foodborne – spread through eating contaminated food, such as raw or undercooked meat, unpasteurized milk, or fresh produce contaminated by the feces of an infected animal. Either pet food or human food can be contaminated and cause illness. Waterborne – spread through drinking or direct contact with water contaminated by the urine or feces of an infected animal. It is possible for an animal to be infected with a microorganism and show no signs of illness. However, the animal will still be able to pass along the microorganism to people and cause illness or vice versa.

Leptospirosis, commonly known as “lepto,” is a contagious, bacterial disease that can cause serious damage to the kidney and/or liver. The bacteria that cause leptospirosis are spread through the urine of infected animals, which can get into water or soil and survive there for weeks or months. Dogs contract leptospirosis when the bacteria enter the body through skin or mucous membranes (eyes, nose, or mouth), especially if the skin is broken from a cut or scratch. Drinking contaminated water can also cause infection, and the disease can be passed from a mother dog to her puppies through the placenta. Leptospirosis is a zoonotic disease, meaning it can be transmitted from animals to humans. In humans, leptospirosis can cause flu-like symptoms and may lead to liver or acute kidney injury. 

Hypothyroidism in dogs is typically the result of inflammation or shrinkage of the thyroid gland. The thyroid gland, located in the neck, is responsible for producing hormones that regulate the body’s metabolic rate, or how much energy the body uses to keep cells and organs functioning. In hypothyroidism, the thyroid gland does not produce enough thyroid hormone, leading to a lower metabolic rate. This hormone deficiency and lower metabolic rate affects the function of multiple organ systems to varying degrees. Hypothyroidism is the most common hormonal imbalance in dogs. This condition is most frequently seen in dogs aged 4 to 10 years and tends to occur in medium and large breed dogs.