Category Archives: Internal diseases of Dogs


Roundworms, also known as ascarids, have round bodies and are 7-12 cm long. They live in  dogs’ intestines on partially digested food.

Pups infested with roundworms lose weight and look pot-bellied. They lose their appetites and may vomit or develop diarrhoea. Serious roundworm infestations obstruct or twist the bowel.

Most puppies acquire roundworm infection from their mothers before birth and then through the milk afterward.

Both puppies and adult dogs are also infected by swallowing roundworm eggs from bowls, hair or dirt contaminated with faeces. They can also be infected by roundworm larvae encysted in the organs of prey like mice, cockroaches, earthworms and chickens.

Ingested larvae and eggs are activated in the dog’s stomach and small intestine and migrate through the muscle, liver, and lungs. After several weeks, the larvae make their way back to the intestine to mature. When these worms begin to reproduce, new eggs will pass in the dog’s faeces, and the life cycle of the parasite is completed.

Roundworm eggs in the faeces confirm roundworm infestation. Because roundworm don’t produce many eggs we sometimes have to examine several fecal samples before we find eggs. Occasionally, we see mature worms in the dog’s vomit or faeces.

Treatment with broad-spectrum wormers like Milbemax or Drontal eliminates adult roundworm. No treatment reliably kills the migrating larvae so we give two or three treatments 2 weeks apart catch them as they mature into adult worms.

The eggs are resistant to most disinfectants and survive in quite harsh environmental conditions. They remain infective to dogs and humans for years.

Regular removal of dog faeces and deworming as detailed below prevent reinfection.

Roundworms are a risk to human health.  Children and people who are immunosuppressed or on immunosuppressive drugs are particularly vulnerable. The roundworm eggs only develop as far as larvae in people. As the larvae migrate through the body they can cause damage, particularly to the eye. Worming people does not kill the larvae as only adult worms are susceptible to wormers. To prevention human infestation

  • Deworm pups fortnightly until 12 weeks of age, then monthly until 6 months of age. Adult dogs must be dewormed every 3 months
  • Remove and dispose of dog faeces promptly
  • Teach children to wash their hands thoroughly after playing with dogs
  • Deworm pregnant bitches in late pregnancy and then every time her pups are dewormed, as above
  • Discourage dogs from defecating in children’s play areas



Whipworms live in the large intestine of dogs and irritate the lining causing watery, bloody diarrhoea and weight loss.

Whipworms produce microscopic eggs that pass out in the dog’s faeces. The eggs resist drying and heat, and can infect another dog years later. Dogs housed on dirt or grass that is not regularly cleaned of faeces risk whipworm infestation.


Whipworm eggs in the faeces confirm a whipworm infestation. However, they are often hard to find as the worms only produce small numbers of eggs on an irregular basis. Any dog with chronic diarrhoea could have whipworms despite negative faecal examinations. Response to treatment indicates that whipworms were present after all.

Most broad spectrum wormers, including Milbemax and Drontal are effective against whipworms.

Whipworms are not infectious to people. They are only parasites of the dog.


Parvovirus in dogs

Parvovirus causes severe vomiting and diarrhoea and is very contagious. The virus may infect a whole litter of pups from an unvaccinated bitch. Dogs less than one year old are the most vulnerable to the virus.

Dogs go off their food and start to vomit within a few days of infection. An astute owner will notice a drop in appetite, depression, and fever before the vomiting and diarrhoea start. The diarrhoea often contains blood and mucus, and many dogs suffer severe pain in the belly.

How does a dog become infected with parvovirus?

The faeces of an infected dog is high in virus. Direct contact between dogs is not required to spread the virus.

Another dog is infected by licking the virus off food dishes, hair, the ground, shoes, clothes, tyres or other objects.  The virus survives for years in backyards.

How do we know it is parvovirus?

We suspect parvovirus in any vomiting dog, particularly if they are unvaccinated and young.  A rapid test for virus in the faeces confirms the infection. Occasionally, even though a dog  has parvovirus the test is negative because the virus has not travelled all the way down the intestine. If we still strongly suspect parvovirus we treat the pup in the isolation ward and retest later.

Can it be treated successfully?

No treatment kills the virus. We treat the dog symptomatically to replace lost fluids, rebalance electrolytes and prevent septicaemia. The virus causes loss of the lining of the intestinal tract. This results in severe dehydration and electrolyte imbalances, and allows bacteria to get into the bloodstream and cause septicaemia.

Pain relief and drugs to control the vomiting are often necessary.

Most dogs with parvovirus recover with aggressive treatment as long as it is begun before severe septicaemia and dehydration occur. Some breeds, notably the Rottweiler, have a much higher fatality rate than other breeds.

Can it be prevented?

Routine vaccination provides excellent protection against parvovirus. We vaccinate pups at 6-8 weeks, 10-12 weeks and then again at 14-16 weeks. In a parvovirus epidemic vaccination at two week intervals is recommended. Rottweilers and pups in an infected yard may need an additional booster at 18 to 20 weeks of age. A booster 12 months after the initial series of vaccinations and then every 3 years protects most dogs against infection.

Bitches should be vaccinated before whelping so that puppies are protected for the first vulnerable weeks of life

How do we kill the virus in the environment?

Disinfect food and water bowls, floors, towels and other contaminated items with chlorine bleach or a glutaraldehyde-based disinfectant at the recommended dilution.

Parvovirus is not transmissible to cats or humans.


Cushing’s disease

In dogs with Cushing’s disease the adrenal glands overproduce some of the body’s regulators, particularly cortisol.

What are the signs of Cushing’s disease?

The most common signs of Cushing’s disease are marked increases in appetite, water consumption and urination. Lethargy, panting and a poor hair coat are also common. We often see a pot-bellied or bloated abdomen due to increased fat within the abdominal organs and thinning of the muscular abdominal wall.

What causes Cushing’s disease?

The three major causes of Cushing’s Disease:

  1. A tumour of the pituitary gland, that stimulates the adrenal glands to produce excessive  amounts of cortisol.
  2. Excessive administration of synthetic cortisones cortisones such as prednisolone, triamcinolone or dexamethasone may cause Iatrogenic Cushing’s disease.
  3. An adrenal gland tumour is an uncommon cause of Cushing’s Disease.

If we suspect Cushing’s Disease we run a blood test to check your dog’s general health. An enzyme called Alkaline Phosphatase (ALKP) is often high in dogs with Cushing’s disease. A Low Dose Dexamethasone test (LDDT) confirms or denies Cushing’s disease.

To determine which type of Cushing’s disease your pet has, we ultrasound the adrenal glands and/or do an endogenous ACTH blood test.

What are the treatment options?

Pituitary Tumour: This is the most common cause of Cushing’s disease. There are two treatment options for it. Trilostane is our drug of choice. A daily capsule of Trilostane reduces the production of cortisone and another important hormone, aldosterone.  We monitor your dog’s response to Trilostane with a test called the ACTH stimulation test. Too little Trilostane won’t reduce appetite or water consumption but too much will cause illness.

If your dog has liver or kidney disease we may suggest treatment with Mitotane (also known as Lysodren). This drug destroys part of the adrenal gland. Careful monitoring and good communication with your vet is necessary during the initial intensive treatment to achieve good results and avoid life-threatening adrenal damage.

Although the pituitary tumour remains present and continues to stimulate the adrenal gland if the tumour is small successful control for many years in most dogs is possible.  If the tumour is large, it may invade surrounding brain tissue and cause other signs, but this is rare.

Iatrogenic Cushing’s Disease: To treat this type of Cushing’s disease we must stop the synthetic cortisone in a very controlled way. If we stop intensive cortisone treatment abruptly your dog may lose his appetite, vomit, develop diarrhea and collapse. The suppressed adrenal gland takes a while to regain normal production of cortisol.

Treatment of an Adrenal Tumour:

Adrenal tumours tend to invade surrounding tissue but if we can surgically remove it all and it is not malignant your dog will regain normal health. Otherwise we treat adrenal tumours with Trilostane also.

Inflammatory bowel disease

Inflammatory Bowel Disease (IBD) is a chronic disease of the gut, or gastrointestinal tract. Most affected dogs have a history of recurrent or chronic vomiting and/or diarrhoea. They may lose weight but are otherwise normal. Most eat well or have an increased appetite, and appear normal.


Inflammatory cells invade the lining of the bowel causing thickening of the bowel. This interferes with digestion and absorption of nutrients and with normal movement of the bowel.

When the cells invade the stomach walls or upper small intestine vomiting develops. Infiltration of the small intestine causes watery diarrhoea and weight loss. Infiltration of the large intestine causes diarrhoea coated with mucus and fresh blood. The entire gastrointestinal tract is sometimes affected.

Something in the diet triggers the disease in some dogs. Bacterial proteins are involved in other cases. In most cases we cannot find any underlying cause.


IBD is diagnosed by ruling out other diseases. Blood tests rule out liver or kidney disease, pancreatic insufficiency and diabetes. Faecal tests rule out parasites like whipworms or giardia.

X-rays or ultrasound rule out some tumours or cancers in the abdomen.

If these tests are all clear we trial special low allergy, low residue or high fibre diets, depending on the part of the bowel most involved.  If bacterial overgrowth is present we trial various antibiotics until we see improvement.

If there is no improvement we biopsy the bowel and a pathologist identifies the type of cells involved, assesses the severity of the inflammation and checks for cancer cells.


If any diet has improved the condition we continue it.

Medication controls (not cures) the problem. We trial drugs like metronidazole, prednisolone and azathioprine until we find what suppresses the signs best. Most dogs stay on the appropriate drugs and diet for life.


The thyroid gland regulates the body’s metabolic rate. When it slows down the whole body slows down.

Hypothyroidism is a deficiency in production of the thyroid hormone. This deficiency is caused by immune-mediated destruction of the thyroid gland, most commonly, or by natural atrophy of the gland.

Signs of hypothyroidism include:

  • Weight gain
  • Lethargy
  • Cold intolerance
  • Dry coat and excessive shedding of hair
  • Very thin coat
  • Increased pigmentation of the skin
  • Failure to re-grow hair after clipping or shaving
  • A tragic expression because of thickening of the facial skin
  • Abnormal nerve function exhibited as non-painful lameness, dragging of the feet, lack of co-ordination and a head tilt
  • Loss of libido and infertility in intact males
  • Lack of heat periods, infertility, and abortion in females
  • Spots on the eyes
  • Dry eye because of inadequate tear production.
  • Anaemia

The thyroid glands are located in the neck either side of the trachea or windpipe. They are controlled by the body’s master gland, the pituitary gland, located at the base of the brain.


To confirm hypothyroidism we test blood to see if T4, the main thyroid hormone, is low. Unfortunately, dogs sick for some other reason or taking certain drugs like seizure medications, may have low levels too. Confirmation of hypothyroidism sometimes requires an additional test.

Hypothyroidism is treated daily with tablets containing a thyroid replacement hormone, thyroxine, for the rest of the dog’s life.

We check T4 levels again after a month of treatment to make sure we are giving the right dose. We test 4-6 hours after the morning dose. T4 levels are then checked every 6 months and the dose adjusted if necessary.

Overdosing produces signs of hyperthyroidism including hyperactivity, lack of sleep, weight loss, panting, nervousness, aggressive behaviour and an increase in water consumption. If any of these occur, please let us know immediately.

Haemorrhagic gastroenteritis

Dogs affected with haemorrhagic gastroenteritis (HGE) vomit and pass diarrhoea with blood in it.  It develops rapidly and sometimes owners just find their dog collapsed.

HGE is more common in small breeds of dogs. A very high red blood cell concentration, measured as the packed cell volume, PCV, or haematocrit is characteristic of HGE. Most normal dogs have hæmatocrits of 37-55%. Dogs with HGE have hæmatocrits over 60%.

We don’t know the exact cause of HGE.

We rule out other causes of vomiting and bloody diarrhoea while we start emergency treatment for HGE.  These causes include stomach ulcers, trauma, worms, other gut parasites, gastrointestinal tumours, intestinal obstruction, foreign bodies, parvovirus, and coagulation disorders.

Dogs with HGE are very ill and if left untreated die. In most cases, it runs its course in a few days with intravenous fluid therapy to combat the dehydration and shock. We give other treatments like antibiotics, anti-ulcer medication and corticosteroids as indicated.

If intravenous fluid therapy is not given the haematocrit continues to rise and the blood becomes so thick that it can hardly flow. A clotting disorder called disseminated intravascular coagulation develops which is often irreversible and fatal.

Collapsing tracheas

Collapsing tracheas are common in small dogs like Chihuahuas, Pomeranians, Shih Tzus, Lhasa Apsos, Toy Poodles, and Yorkshire Terriers.

The trachea, also known as the windpipe, connects the throat to the lungs. The normal trachea is tubular and maintains its shape with a series of “C” shaped rings made of cartilage.

When a dog with a collapsing trachea breathes in, the cartilage rings flatten from top to the bottom. This makes it difficult for air to enter the lungs and causes a chronic, honking cough.

In affected dogs the cartilage rings lose their stiffness and cannot retain their circular shape.

Coughing is often worse in the daytime. The cough is exacerbated by excitement, drinking water, eating, or pressure on the trachea, particularly from a leash.

We suspect a collapsed trachea in a small dog with a persistent dry and/or honking cough. If light pressure over the trachea causes a cough we recommend a chest X ray to rule out other heart, lung and airway problems. These other conditions are common in small dogs and they often suffer from several of them at a time.

Endoscopy allows us to watch the inside of the trachea during inspiration and expiration for signs of collapse.

We treat a dog with collapsing trachea with drugs to open up and reduce inflammation of the airways.

Antibiotics control infections of collapsed airways, which are common.

Weight loss reduces pressure on the airways in obese dogs. A low fat diet and mild exercise helps them shed the extra kilos.

Avoid exacerbating the cough with excitement and vigorous exercise.

Because medical therapy only treats the cough and does not correct the problem, affected dogs will always have a bit of a cough. Our aim is to minimize the cough, and make them more comfortable and active.

Bladder stones

Bladder stones form from minerals excreted into the urinary bladder. They range in size from grains of sand or tiny pebbles to a large, single stone.

The main signs of bladder stones are blood in the urine (hæmaturia) and straining to urinate (dysuria). Urinary tract infections also cause hæmaturia and dysuria.

Hæmaturia occurs because the stones mechanically irritate the bladder wall and make it bleed.

Dysuria occurs when stones obstruct the passage of urine out of the bladder. Large stones sometimes cause a valve-like obstruction at the neck of the bladder. The dog passes some urine and then despite straining cannot pass more. Small stones flow with the urine and obstruct the urethra, especially of male dogs.

Stones form from a high concentration of crystals in the urine. The crystals form because of abnormalities in the diet or because of disease in the bladder, especially bacterial infection. Sometimes they form because of a fault in body chemistry.

We suspect bladder stones if the bladder is painful or when there are recurrent infections. We can feel some bladder stones through the abdominal wall but most bladder stones are diagnosed with x-rays or ultrasound.

The fastest treatment is surgery to open the abdomen and bladder and pick out the stones.

Alternatively, if the dog has passed a stone in the urine we analyse it and prescribe the specific diet that dissolves that type of stone. Diet is not successful in dissolving some kinds of stone and is not fast enough if the pet is already toxic from a back up of urine in the urinary tract.

Some types of stone can be prevented. Regular tests for urinary tract infections and appropriate antimicrobial treatment prevent stones formed as a result of bacterial infection.

Specially formulated diets help prevent the formation of some other types of stone. We determine the chemical composition of stones removed at surgery and prescribe the best preventative diet for that particular type of stone.

Puppy vaccination changes

Pups should be have their final vaccination for distemper, hepatitis and parvovirus at 14-16 weeks according to the latest recommendations from the World Small Animal Veterinary Association.

High levels of protection from the dam may interfere with the pup’s own immunity up to the age of 14 weeks, according to recent research. As we cannot be sure of any individual’s level of protection we recommend that all pups have a last vaccination after 14 weeks.

We have changed our puppy vaccination protocol to 3 vaccinations: at 6-8 weeks, 10-12 weeks and 14-16 weeks.

Some breeds, such as Rottweilers, are late developing immunity to parvovirus, and we have always recommended a third needle for them.