Seasonal Canine Illness

What is Seasonal Canine Illness, and Should You Be Worried About It?

Seasonal Canine Illness (SCI), sometimes called Canine Seasonal Illness, is a (relatively) newly recognised disease in dogs – the first cases were detected in 2010. Cases peak in autumn – mainly September. The disease is still uncommon, but it can be serious – hence the need to be aware of it. SCI causes severe vomiting and diarrhoea in dogs. When the disease was first discovered 20% of dogs were dying from the symptoms but within two years this had reduced to 2%. Now the disease is rarely fatal, but dogs can be unwell for 7-10 days.

SCI was first detected on the Sandringham Estate in Norfolk. East Anglia, Lincolnshire and Nottinghamshire remain higher-risk areas, but cases have been seen more widely. If you are holidaying in the East with your dogs this autumn, the risk of SCI is slightly higher. Dogs that have walked in woodland and dogs that have harvest mites (see below) are believed to be at greater risk too.

What Causes SCI?

Sadly, the cause of SCI remains unknown. The Animal Health Trust, based in Newmarket, was conducting research into the disease. Most of what is known about SCI is from their research. Sadly, however, they were forced to close in 2020 and research is not ongoing.

A few potential causes, such as mushroom poisoning, chemicals, natural flora, or exposure to algae have been discounted. There is a strong link between symptoms and dogs that have recently walked in woodland. There is also a link to harvest mite infection in many cases.

What Are Harvest Mites?

Harvest mites (Neotrombicula autumnalis) are tiny mites, just visible to the human eye. You can see them on your dog if you look carefully – they look like orange dust. They climb onto dogs and attach to feed in thin-skinned areas such as the inside of the ears, or between the toes. They cause intense itching, irritation, and reddened skin. Harvest mites are most common in Autumn.

Many dogs diagnosed with SCI have had harvest mites – but not all dogs with harvest mites have SCI. Scientists wondered if the mites might carry a virus that affects dogs - causing SCI -  (among other theories) but nothing has been proven.

What are the signs of SCI?

Dogs with SCI tend to show the following signs of illness:

  • Vomiting
  • Diarrhoea
  • Tiredness due to dehydration
  • Blood in their vomit and/or stool

Dogs may also have some the following:

  • Abdominal pain
  • Inappetence
  • Fever
  • Muscle tremors

These signs of illness are not disease-specific, and there are many, far more common, causes of vomiting and diarrhoea in dogs than SCI. However, SCI cases tend to become severe within a few hours and lead to dehydration quite rapidly – which requires veterinary treatment. Symptoms are usually within 72 hours of a woodland walk. There is often blood in the vomit and diarrhoea too.

Is SCI Life-Threatening?

Dogs with SCI may be very poorly, but most will make a full recovery with appropriate treatment. Some have died from the disease, but this is not expected. Dogs that are more likely to get seriously ill would be the very old, the very young, and those with other health problems.

What is the Treatment for SCI?

Even though the cause of SCI is not fully understood, treatment is usually successful with dogs making a full recovery within 10 days. Treatment is centred around controlling the symptoms rather than eliminating the underlying cause – because the cause is unknown.

Treatment is likely to include fluid therapy to combat dehydration, pain relief for abdominal pain, anti-nausea medication to help control vomiting, and a bland but nutritious diet once the patient is eating. Many vets will also prescribe antibiotics – whilst a bacterial infection as the cause is not proven, affected dogs are often very ill and it is wise to cover all eventualities.

How Do I Know Whether to Worry if My Dog is Sick?

There are lots of causes of vomiting, diarrhoea, tiredness, and tummy ache in dogs – it’s one of the main things we see dogs for in Practice. The most common reason for these symptoms is a dog eating something they shouldn’t have – maybe a treat they’ve not had before, or too many chews, or something they have scavenged under a bench in the park.

Many dogs with signs of tummy upset will recover within 24 hours at home, without seeming particularly ill and without seeing a vet. Many others do need some treatment but often take their treatment at home and make a full recovery within a few days.

We do see more serious tummy upsets too and some dogs will need to be admitted as in-patients. This may be for tests – to check for things like an obstruction to the stomach or intestines, liver disease, pancreatic disease or other medical problems, or an infection. Dogs may also need to be inpatients so we can administer fluids to treat dehydration, or to have their medication by injection if they’re not eating.

The time to worry is if your dog starts to vomit and becomes very subdued within a few hours, especially if there is blood in the vomit. Any dog that is very off-colour and vomiting should be seen by a vet, whatever the cause, as they may need urgent treatment. If you have recently walked in woodland, visited the East of England, or seen harvest mites on your dog, these are additional red flags.

Reaching a Diagnosis?

When treating a dog for an upset tummy, it is not always necessary to reach an exact diagnosis – it’s ok just to treat the symptoms – and that’s because reaching a diagnosis can mean lots of expensive tests that don’t help your dog to get better. If tummy upsets are mild and respond well to initial treatment, then we may never know what caused them, and that’s okay.

What’s tricky is when tummy upsets get more serious, and reaching a diagnosis becomes important for us so we can make sure your dog is on the correct course of treatment.

As an example, a dog that is not keen to eat and is vomiting a lot, with a painful tummy may:

  • Have something stuck in their intestines or stomach and need urgent surgery to remove it, as it would become life-threatening if ignored.
  • Have swelling of their pancreas and need targeted medical treatment and diet changes to prevent the condition from becoming life-threatening.
  • Have had a bad reaction to a new food or similar which needs supportive treatment like fluid therapy and tummy-calming medicines.
  • Have a specific infection or poisoning which requires a specific treatment like antibiotics, or a particular antidote.

If one of us suggests that we admit your dog for tests and treatment, it’s because we’re worried that their symptoms are particularly severe, or they’re not getting better with standard treatment. We may suggest testing to narrow down the possible causes of their symptoms, so we can start the best treatment ASAP. Broader tests, like blood screening and x-rays or ultrasound examinations, are more likely to be done first.

SCI is diagnosed in dogs that meet the risk factors and show the signs, and where tests have not revealed another cause. 


SCI is a serious illness that can make dogs extremely poorly within a few hours of first becoming unwell. However, it is usually treated successfully, even though the cause remains unknown. Cases have been mainly reported in the East of England in dogs that have walked in large forests in that area. There is evidence that SCI may be linked to harvest mites, but this is unproven.

Treatment is likely to include fluids, tummy-settling meds, pain relief and antibiotics. Tests may be necessary to rule out other causes of severe vomiting that need alternative courses of treatment.

SCI is not a major worry in our area, but any dog that has severe vomiting or diarrhoea and quickly becomes subdued should be examined by a vet. Whatever the cause, it could be very serious, and early veterinary attention is likely to be of great benefit for these patients.