Diabetes mellitus is an endocrine disorder that leads to high levels of glucose (a type of sugar) in the blood. Diabetes is common in dogs and cats. November is Pet Diabetes Month, so this article is a brief overview of this complex disorder.
 
Causes
Carbohydrates in the diet are converted to glucose in the body. The hormone insulin helps move glucose from the bloodstream into cells, where glucose is a source of energy. Diabetes mellitus occurs either when the body doesn’t produce enough insulin or when the body can’t use insulin properly.
 
Insulin is made in the pancreas. Immune-mediated destruction of pancreatic cells or pancreatitis (inflammation of the pancreas) can reduce insulin production. Dogs and cats can also develop insulin resistance, in which the pancreas makes insulin but the body doesn’t respond normally to it.[1] This type of diabetes, similar to type 2 diabetes in people, is the most common type in cats.[2]
 
Risk Factors
Obesity is a major risk factor for diabetes in dogs and cats. Obese cats are up to 4 times as likely as cats of ideal weight to develop diabetes.[2] Other diseases, like hyperadrenocorticism (Cushing disease) and hypothyroidism in dogs, acromegaly in cats, dental disease, and kidney disease, are also associated with diabetes. Some medications, especially glucocorticoids like prednisone, increase the risk for diabetes. Breeds that are more prone than others to diabetes include beagles, Australian terriers, Samoyeds, keeshonds, and Burmese cats.[1]
 
Symptoms
In animals with a high blood glucose level, excess glucose is excreted in the urine. Glucose in the urine acts as a diuretic, increasing urine volume. Animals with diabetes often develop urinary tract infections because of the sugar in the urine. When cells can’t use glucose properly for fuel, the body begins to break down fat and muscle. These changes in metabolism affect many organ systems. Uncontrolled diabetes can also lead to diabetic ketoacidosis, a potentially life-threatening complication.
 
These are some of the symptoms of diabetes:

• Increased thirst
• Increased urine volume (for cats, look for larger urine clumps in the litter box)
• Urinating in inappropriate locations
• Increased appetite
• Weight loss
• Cataracts in dogs
• Odd gait or stance, especially of the hind legs, in cats
• Decreased energy
• Weakness
• Ketoacidosis symptoms: vomiting, loss of appetite, lethargy, coma

 
Diagnosis
Diabetes is diagnosed by blood and urine tests showing high glucose levels that persist on repeat testing. In cats, stress can increase the blood glucose level, so measurement of serum fructosamine (a protein that reflects average blood glucose levels over the previous week or so) can help with diagnosis. Full bloodwork, urinalysis, and urine culture are done to identify other conditions that might accompany or result from diabetes and complicate treatment.
 
Treatment
Dogs and cats with diabetes are treated with insulin injections and diet modification. Oral medications for diabetes don’t work for dogs and aren’t very effective in cats, so all dogs and almost all cats with diabetes require insulin injections.[1] The type and dose of insulin and the diet chosen depend on the individual patient and can change over time.
 
Other disorders can affect the body’s response to insulin and must also be identified and treated. Sick patients with ketoacidosis need intensive treatment in the hospital.
 
Treating diabetes requires significant pet owner commitment and regular monitoring. The injections must be given on a consistent schedule, and owners need to monitor their pet’s appetite and watch for signs of hypoglycemia (low blood glucose): sleepiness, weakness, stumbling, tremors, and seizures. In dogs and cats, blood glucose is monitored from time to time with a glucose curve, a series of glucose measurements over the course of a day, either at home or at the veterinary clinic. Insulin dose adjustments are generally based on glucose curve results, not on single spot checks of blood glucose.
 
Prognosis
In dogs, diabetes almost always requires lifelong insulin therapy. Some cats treated for diabetes undergo remission and no longer need insulin, especially if their blood glucose levels can be brought under control with insulin and diet early in the course of disease.[1] The prognosis is generally good for dogs and cats with well-controlled diabetes.
 
References
1. Behrend E, Holford A, Lathan P, Rucinsky R, Schulman R. 2018 AAHA diabetes management guidelines for dogs and cats. American Animal Hospital Association. 2018. Accessed November 20, 2020. https://www.aaha.org/globalassets/02-guidelines/diabetes/diabetes-guidelines_final.pdf
2. Sparkes AH, Cannon M, Church D, et al; ISFM. ISFM consensus guidelines on the practical management of diabetes mellitus in cats. J Feline Med Surg. 2015;17(3):235-250. doi:10.1177/1098612X15571880
 
Photo by Mustang Joe

Zoonotic diseases are diseases transmitted between people and animals. An estimated 75% of emerging infectious diseases in humans have an animal origin.[1] Because people and animals share habitats, environmental health is linked to both human and animal health. Changes in environmental conditions can increase the risk of zoonotic disease spread.
 
One Health is the concept that human, animal, and environmental health are connected and that professionals in all of these areas need to work together to solve global health problems. The COVID-19 pandemic, caused by the zoonotic virus SARS-CoV-2, has highlighted the importance of using a One Health approach to manage emerging diseases.[2]
 
Connections Between Human and Animal Health
COVID-19 is not the first pandemic caused by a zoonotic agent. The Black Death was a bacterial infection spread in part by rat fleas, and the 1918 flu pandemic was caused by an avian influenza virus. The more recent coronavirus epidemics SARS (severe acute respiratory syndrome) and MERS (Middle East respiratory syndrome) both had animal origins.[2] Many other diseases originating in animals have serious consequences in people. These are just a few examples:

• Rabies
• Anthrax
• Ebola
• HIV/AIDS
• Brucellosis
• Salmonella infection
• H1N1 swine influenza

 
People spread pathogens to animals too. For example, humans can transmit SARS-CoV-2 to companion animals like cats and dogs. Some infectious agents (bacteria, for instance) move in both directions between humans and nonhuman animals. Contaminated water endangers people and animals alike.
 
Cross-species disease transmission is not necessarily direct. In some cases, viruses circulating in an animal population undergo genetic changes and are then able to infect a new species. Some pathogens spread from one species to another through multiple intermediate host species. Others require vectors—carriers like mosquitoes—to infect new hosts.
 
The One Health approach recognizes multiple factors that can influence disease spread:

• Expansion of humans into new geographic areas, encroaching on wildlife habitats
• Close contact between humans and livestock
• Shared living spaces for humans and companion animals
• Increased travel and trade, allowing pathogens to move worldwide
• Antimicrobial resistance, which endangers animal health, human health, and the food supply
• Contamination of the environment
• Deforestation and habitat disruption through inappropriate farming practices
• Effects of climate change on animal populations and ecosystems[3]

 
Emerging Diseases and the Environment
The reasons new infectious diseases emerge in humans can be lumped into 3 categories:

• Changes in the pathogen, such as a virus mutating
• Host factors: individual factors (like immune function) and population factors (like crowding behavior and population growth)
  
• Environmental changes, mostly caused by human behavior[4]

 
Climate change and extreme weather affect the movement of wildlife that carry zoonotic diseases. The geographic spread of some vector-borne diseases has increased as climate change (warming) expands the range of the insects that transmit them.[3] Any human behavior that increases human contact with wildlife (like legal or illegal wildlife trade), decreases natural habitats, alters ecosystems, or reduces species diversity can increase the risk of zoonotic disease spread.
 
International Collaboration
A number of agencies worldwide are involved in One Health collaborations. In the United States, the One Health Office is located in the National Center for Emerging and Zoonotic Infectious Diseases, part of the Centers for Disease Control and Prevention. The World Health Organization, Food and Agriculture Organization of the United Nations, and World Organisation for Animal Health work together to develop global health strategies. Many other organizations are collaborating across disciplines to study and manage zoonotic diseases.
 
References
1. Zoonotic diseases. Centers for Disease Control and Prevention. Accessed November 3, 2020. https://www.cdc.gov/onehealth/basics/zoonotic-diseases.html
2. Deem SL, Brenn-White M. One Health—the key to preventing COVID-19 from becoming the new normal. Mol Front J. Published online September 30, 2020. doi:10.1142/S2529732520400039
3. One Health basics. Centers for Disease Control and Prevention. Accessed November 3, 2020. https://www.cdc.gov/onehealth/basics/index.html
4. Morens DM, Fauci AS. Emerging pandemic diseases: how we got to COVID-19. Cell. 2020;182(5):1077-1092. doi:10.1016/j.cell.2020.08.021
 
Image source: Centers for Disease Control and Prevention, National Center for Emerging and Zoonotic Infectious Diseases