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About Dog Illnesses

Dog illnesses can be mild, severe or even deadly and there are a wide variety of symptoms, and a range of treatment options.

It can be difficult for dog owners to tell the difference between something benign and something serious, especially in the early stages of illness.

If you think Fido is sick, he needs to be examined by a veterinarian so that you can make sure Fido gets the right treatment. The earlier you treat a problem the quicker it will be to resolve, and the less costly the treatment.

On this page you'll find a list of symptoms most frequently seen in dogs who are sick, and information on common canine illnesses and diseases.

Yorshire Terrier

I've also included an article written exclusively for this website by veterinarian Dr. Megan Teiber, DVM.

In it, she shares tips on how to recognize the signs that your dog is ill, how veterinarians reach a diagnosis, and the best way to keep your dog healthy in the first place.

Common Symptoms of Illness in Dogs

  • Diarrhea
  • Vomiting
  • Loss of appetite
  • Lethargy or exhaustion
  • Runny nose
  • Cough
  • Sneezing
  • Fever (anything over 104F)
  • Eye discharge
  • Swollen lymph nodes
  • Skin inflammation/rash
  • Disorientation
  • Shaking or trembling
  • Convulsion
  • Behavioral changes (eg. panting, pacing, whining)

Many of the above symptoms are found in a number of different diseases and conditions.

Vomiting, Diarrhea, Lethargy, Fever

Diarrhea, vomiting and lethargy are extremely common and can be signs of a simple tummy upset or a serious illness. If your pup or dog also has a fever he could have a contagious illness. Possibilities include:

Nasal Discharge, Eye Discharge, Fever, Cough

These four symptoms (or any combination of them) could signal contagious diseases such as:

More Dog Illness Symptoms

Other signs that your dog isn't well might include slightly less obvious symptoms such as:

  • Itching
  • Hair loss
  • Inflamed or irritated skin
  • Excessive thirst
  • Loss of appetite
  • Increased appetite
  • Weight loss
  • Weight gain
  • Difficulty breathing
  • Bad breath
  • Lameness 
  • Loss of co-ordination

In addition to the diseases and conditions listed above, there are a lot of other illnesses that your dog could develop, both contagious and non-contagious.

Non-contagious Dog Illnesses

Poodle with diarrhea

Being able to recognize signs of a medical emergency in your dog could save his life.

This article discusses dog emergency symptoms in detail and will help you decide whether or not Fido needs an urgent trip to your veterinarian or 24-hour emergency pet hospital.

Dog Illnesses - A Veterinarians' View

Signs that all is not well:

Some signs of disease in dogs, such as vomiting, diarrhea, coughing, limping, or itching are pretty obvious to all pet owners. Others can be more vague.  But no one knows your dog better than you.  If you notice subtle changes in your dog’s personality, appetite, and energy levels, it is worth a trip to your vet. 

Personality changes may not be the same for every dog---a dog who is normally at your side all day may suddenly be more elusive, and a dog who is normally aloof may be more clingy. A Labrador who normally chows down every meal and suddenly refuses breakfast is a big deal, while skipping a meal probably would not be concerning for a dog who routinely picks at his food. 

Other common signs of dog illnesses that are easily missed include increased water consumption or urination, unintended weight loss, panting, and restlessness at night. When in doubt about whether your dog is sick, err on the side of caution.  It is better to get a clean bill of health from the vet and breathe a sigh of relief, than to find out too late that a serious illness was brewing all along. 

Reaching a veterinary diagnosis:

When you bring your dog to the vet for an illness, we will perform a full physical exam.  Sometimes the problem is obvious based on exam findings.  However, there are many times the exam is normal or does not give the answers we need. This is especially true if the dog’s symptoms are nonspecific or vague.   

If a dog is limping, it is pretty obvious we need to look at the affected leg, and if he is itching we need to look at his skin.  But if he isn’t eating well or is just more lethargic than normal, it could be just about anything! Where do we start?  

First, we consider your dog’s signalment. This is the age, sex, and breed, and it helps narrow down the list of probable diagnoses. For example, if a young dog is vomiting, we first consider intestinal parasites, dietary issues, or foreign body intestinal obstruction.  If the dog is older, we may be more likely to consider liver disease, kidney failure or cancer as possibilities. 

The breed is also important, as some breeds are more prone to certain canine illnesses than others.  For example, German Shepherd Dogs are the poster children for pancreatic insufficiency.  If they come to me for ongoing diarrhea and weight loss, it I would test for this disease early.  If the dog was a Chihuahua, I would consider this disease less likely and not pursue the testing right away. 

The next thing we’ll do is get a good history. It is important that the person who knows the dog best is the one that brings him to the vet.  We want to know your dog’s regular diet, if he’s on any medications, if he got into anything he shouldn’t have, if he’s been around other dogs, his vaccination history, if he’s had this problem before, and how long the symptoms have been happening. The answers to these questions may influence what diagnostic testing we recommend. 

Let’s take vomiting, for example.... if a young dog is vomiting very frequently for the last 2 days and has a history of eating socks, I would be likely recommend x-rays to look for intestinal obstruction.  If he’s older, vomiting on and off for a few weeks, and gradually losing weight, I’d be more likely to recommend bloodwork to check his organ function.  Of course, not every dog follows the rules, but these are good starting points.  

After considering exam findings, signalment, and history, we select the most reasonable diagnostic tests to recommend.  If your dog is severely ill, we may conduct multiple tests right away to get to the bottom of the problem as quickly as possible. 

If the symptoms are more mild or chronic, we may start with one test and take things step by step.  Sometimes, despite our best efforts, we don’t reach a definitive diagnosis. Tests can be normal or inconclusive, or they may be declined by pet owners due to cost or feasibility.  In these cases, we usually suggest supportive treatment.  This may mean fluids, anti-nausea medications, or pain medications to help your dog feel better even though we aren’t sure exactly what’s going on.  Sometimes this solves the problem.  If it doesn’t, we need to be more aggressive in our diagnostic testing.

Prevention Tips:

Lastly, there are things you can do as pet owners to prevent dog illnesses, or at least catch them early. The first is to keep your pet vaccinated.  Rabies and Distemper/Hepatitis/Parvovirus vaccines are considered ‘core’ by AAHA (the American Animal Hospital Association) and should be administered to all dogs.  Puppies may need several boosters, while adult dogs can receive vaccines spaced out based on your veterinarian’s recommendations or the laws in your state. 

Leptospirosis and Bordetella (kennel cough) vaccination is also recommended by most veterinarians but may be based on your dog’s lifestyle.  Lyme disease is becoming more common as ticks are more widespread, and many vets are now recommending the Lyme vaccine based on your location.  Canine influenza is another emerging disease and vaccines are recommended for at-risk dogs. 

You can also prevent disease by administering regular heartworm prevention and yearly heartworm tests.  An ounce of prevention is worth a pound of cure---the current preventatives are very safe and heartworm treatment is complex, risky, and expensive. 

The same goes for flea and tick prevention.  Keeping your dog free of fleas and ticks is much easier than battling a flea infestation or treating a tick-borne illness---your dog will thank you for it! 

Lastly, keep up with regular physical exams at your vet’s office.  Remember that dogs age faster than humans, and if they are examined less than 1-2 times per year, we risk missing the warning signs that something is amiss.  As dogs age, it is also recommended to check bloodwork regularly to monitor for organ function.

There are some diseases which are simply not preventable, but by keeping up with regular health checks, we can at least catch things early and intervene before your dog becomes severely ill.

Author: Dr. Megan Teiber, DVM

Other Canine Diseases & Conditions

Veterinarian examining tiny Pitbull puppy


Leptospirosis is a bacterial disease affecting the urinary systemincluding liver and kidneys. Mainly transmitted through infected urine. It is possible for dogs to transmit Leptospirosis to human family members.

Loss of appetite, vomiting, lethargy, fever. More advanced symptoms include jaundice, increased thirst and dehydration due to frequent urination. 

Early antibiotic treatment can lessen the severity and/or duration of this illness.


A highly infectious viral infection of the respiratory system. Easy airborne transmission through coughing and sneezing. 

Include a runny nose, cough and fever.

Mostly supportive, with antibiotics being given for secondary infections.


One of the most well-known, and feared, dog illnesses. A severe and usually fatal virus that affects the brain and nervous system. Transmitted through saliva. Once symptoms appear this illness is always fatal to both dogs and humans. 

Are behavioral and usually include unusual, irrational and frenzied aggression (if your dog was very shy you may see a increased affection or acute shyness if previously friendly). You may also see lack of co-ordination, seizures and the classic foaming at the mouth.

There is no treatment for Rabies and the disease is always fatal.

Canine Hepatitis

Highly contagious viral disease which affects the liver. Starts in tonsils, spreads to lymph nodes, bloodstream and liver. Can be transmitted through urine, feces and saliva. 

Similar to Distemper. Severe cases can progress rapidly and cause sudden death.

Mainly supportive care which may include IV fluids and medications.

Puppy Strangles

Also known as Juvenile Cellulitis, Puppy Pyoderma, Sterile Granulomatous Dermatitis or Lymphadenitis. Fairly uncommon.

An autoimmune disease which usually appears suddenly in puppies under 4 months of age. May have a hereditary component as some breeds are predisposed to developing it. Needs to be treated quickly to avoid serious, or fatal, consequences.

Generally begin with generalized swelling of the puppy's face, but the most noticeable symptom is extreme swelling of the lymph nodes under the jaw and around the neck.

As this progresses it looks as though the puppy is being 'strangled' by the swelling, hence the name. Painful pimples and pustules then develop over the head/muzzle/ears.

Swelling might occur in other lymph nodes and joints, pustules may spread across the body, plus a puppy could lose his appetite and/or have a fever.

Treatment of Puppy Strangles:
Treatment usually consists of corticosteroids to reduce the swelling and inflammation, and antibiotics to kill off any secondary infection that has set up in the affected areas.

If your pup has a severe case, other treatments might be needed, or the standard treatment may need to be maintained for a longer period.


'Pano' is a condition that is most often seen in medium, large or giant breed puppies. Caused by inflammation of the bones, usually in the front legs and it affects puppies between 6 and 18 months old.

A self-limiting disease which means that the majority of puppies will grow out of it without any treatment and without lasting side effects.

Usually a puppy with Panosteitis will have some pain in his legs, and will limp intermittently. Often displays no sign of tenderness to the touch and will allow leg/s to be felt, moved without complaint.

It's usually worse in the morning, after rest, or at the beginning of a walk or play session. Then the puppy 'walks it off' and seems fine.

Usually a pup will suffer on and off for 3 - 6 months and then recover. Occasionally it can be longer.

Occasionally a pup will have a fever, seem lethargic or lose his appetite as well. If this happens he needs to be seen by a vet because treatment might be needed.

Most puppies recover fully without treatment and Pano is just a nuisance, but if your pup has a lot of pain or other symptoms then your vet might prescribe corticosteroids or other anti-inflammatory medications to help him feel better.


Cancer happens when cells grow in an unnatural, out of control, way. These cells are dangerous and can affect not only the organ or area they originate in, but can also spread throughout the body.

Causes can be environment, dietary, genetic and more.

There are so many different types of cancer that dogs can get it's impossible to cover all signs and symptoms but I've included the most common ones. Your dog may have only one of them, or several.

Lumps or swellings, sores that won't heal, weight loss, apptite loss, lethargy, change in bowel habits or stool appearance, weakness, difficulty breathing, trouble peeing or pooping.

Treatment options vary depending on the type and location of the cancer. Lumps or tumors can be removed. Surgery, chemotherapy, radiation, immunotherapy... all the options available to humans are available to our dogs too. Not all cancers can be cured even with aggressive treatment. Quality of life should be considered along with quantity.

Health Alert. New Canine Virus Update

Circovirus is a virus which has previously affected only livestock but has now mutated to the point where it has the potential to be a risk to our dogs because it can cross from one species to another.

Main symptoms of Circovirus are bloody diarrhea, vomiting, lethargy, weakness & loss of appetite.

Other symptoms can include vasculitis (inflammation of blood vessels), rapid heart rate and fluid on the lungs.

Quick diagnosis and prompt treatment give your dog the best chance of survival, so be aware of this very small, but real, risk.

Vizsla dog with stethoscope

A good reference book is worth it's weight in gold, and this is certainly true when you're talking about dog illnesses and other canine health issues.

Here are a few of the best dog health books available, I'd personally recommend having at least one of them on your bookshelf....

All the information and advice on this page has been approved by
Veterinarian, Dr. Megan Teiber, DVM

› Dog Illnesses

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