Yes! Dogs can get encephalitis, that is an inflammation of the brain. This article will help you understand what encephalitis is, its causes and symptoms, as well as how vets go about diagnosing and treating the condition. Recognising the signs early is crucial, as prompt veterinary care can make a significant difference in your dog’s recovery. Read on to learn more about this neurological condition. 

Definition and causes

Encephalitis simply means inflammation of the brain (enceph- referring to the brain; -itis meaning inflammation of). The processes which lead to the brain being inflamed are not so simple; but can generally be divided into infectious and non-infectious causes. 

Infectious encephalitis 

Infection is potentially one of the most well-known causes of encephalitis, however, is much less common that one may expect in the veterinary patient. The exact prevalence varies depending on geographic location and exposure risks but is generally less common than non-infectious causes. Most canine cases (approximately 60%) do not have an identifiable infectious cause. 

When infectious encephalitis does occur, the infection can reach the brain via several routes: 

  1. Blood – infection can spread to blood, travel around the body and settle in the brain. The infection most commonly comes from infections such as lung abscesses and heart infections (endocarditis). Septicaemia (infection of the blood itself) can also cause encephalitits. 
  1. Neighbouring structures – infection can spread from nearby structures, e.g. the ears, or other parts of the central nervous system.  
  1. Outside causes – infection can be introduced to the brain from outside of the body. This can occur from injuries to the skull e.g. suffered during road traffic accidents.  
  1. Ticks – such as Ixodes Ricinus, can introduce infection when they attach themselves to an animal. One such infection is Lyme disease. 

There are several different pathogens which can cause infectious encephalitis. These pathogens can be split into: 

  • Viral e.g. distemper, parvovirus, parainfluenza and herpesvirus. 
  • Bacterial e.g. mycoplasma. 
  • Fungal e.g. cryptococcus, coccidioidomycosis and aspergillus. 
  • Protozoal (single celled organisms, capable of infecting animals) e.g. toxoplasmosis and neosporosis. 

Quick interruption! 

When encephalitis, so inflammation of the brain, occurs it is common for meningitis to occur simultaneously. Meningitis is the inflammation of the meninges (mening- referring to the meninges; -itis meaning inflammation). The meninges are in very close proximity to the brain itself, so it makes sense that both of these structures would be involved when inflammation +/- infection occurs. The meninges actually consist of three layers: the dura mater (outside), arachnoid mater (middle) and pia mater (inside) – so one, or all, may be involved when inflammation occurs. 

So, the infectious causes of encephalitis discussed above could actually be meningoencephalitis (infection of the meninges and brain) depending on the disease process and severity. The non-infectious causes, discussed below, can also affect both structures, again depending on the disease process and severity. 

Non-infectious encephalitis: Immune mediated / autoimmune. 

Immune mediated / autoimmune causes of encephalitis in dogs are not uncommon. This category of encephalitis includes diseases where the immune system attacks its own body. Normally, the immune system is trained to only attack structures which do not originate from the body itself, such as bacteria, viruses and foreign bodies. In immune mediated conditions, the immune system cannot differentiate self from non-self, so accidentally attacks the animal’s own health cells.  

In the case of immune mediated encephalitis, the body attacks the brain, and commonly also attacks the meninges (meningoencephalitis). The term Meningoencephalitis of unknown origin (MUO) is used to describe immune mediated encephalitis as, although we believe the condition to be caused by the animal’s own immune system, we are not always sure why the immune system is attacking itself in the first place. 

Another quick interruption! 

To complicate things further, in cases of immune mediated encephalitis, not only are the meninges commonly also involved (meningoencephalitis) but it is not uncommon for the spinal cord to be involved as well (meningoencephalomyelitis)! 

Back to Meningoencephalitis of unknown origin (MUO) 

Generally speaking, there are three types of MUO: granulomatous meningoencephalomyelitis (GME), necrotising meningoencephalitis (NME) and necrotising leukoencephalitis (NLE). Each one describes a slightly different pattern of disease within the brain – they each affect the brain in slightly different ways. It would be beyond the scope of this article to go into these in more detail, as they are incredibly complicated diseases and they still baffle specialists!  

What are the symptoms of encephalitis? 

The symptoms, or clinical signs, of encephalitis in dogs vary depending on the specific area of the brain affected by inflammation. For instance, the forebrain plays a key role in behaviour, perception, and the animal’s conscious awareness of its surroundings. When inflammation occurs in the forebrain, you may notice behavioural changes, seizures and altered mentation. 

On the other hand, the cerebellum is responsible for maintaining balance and coordination. Inflammation in this area may cause your dog to experience tremors, wobbliness, and significant incoordination, especially while walking.  

Other signs of meningoencephalitis include, but are not limited to: 

  • Stiffness. 
  • Neck pain. 
  • Sensitivity to light and/or touch. 
  • Visual problems including blindness. 
  • Paresis or paralysis. 
  • Odd body position such as body turn or head tilt. 
  • Odd body movement such as walking round in circles. 
  • Systemic signs such as: loss of appetite, vomiting. 

If the underlying cause of the encephalitis is infectious, your pet will likely also have a temperature.  

How is encephalitis diagnosed? 

Diagnosis will be aimed at identifying the underlying cause of the encephalitis. The exact diagnostic tests performed will depend on the exact case, but generally will involve: 

  1. Neurological examination: this will allow your vet to first, determine if the neurological system is involved and second, begin to narrow down where in the brain the signs are originating from. This will involve you vet evaluating your dog’s reflexes, coordination, and responses to stimuli. These tests may include observing your dog’s gait, testing reflexes with gentle taps, and checking responses to light, sound, and touch. 
  1. Blood tests: this can show if other parts of the body are involved and can indicate if an infectious cause is more or less likely.  
  1. Imaging: in an ideal situation an MRI of your dog’s brain will be performed. This will allow us to see what part of the brain is affected and how severe the disease process is. However, occasionally the brain will look completely normal; this may mean that whatever is going on in your dog’s brain is too small for the MRI machine to detect. 
  1. CSF: Cerebrospinal fluid (CSF) is a, normally clear, liquid which lubricates the brain and spinal cord. It carries nutrients and removes waste material, helping to keep the central nervous system healthy. During encephalitis, abnormal cells such as inflammatory cells or bacteria, can be present in CSF; therefore, we need to take a small sample to help us determine the underlying encephalitis cause. CSF sampling in a dog involves collecting a small amount of CSF from the back of their head, at the very top of their spine, or at their lower back. We use a long needle to achieve this so needs to be performed under general anaesthesia. 

What is the treatment? 

Depending on the cause of the encephalitis, there are often medical treatments available. If bacterial in origin, antibiotics will be needed. If immune mediated, immunosuppressants may be used. Then, pain relief, anti-inflammatories or anti-sickness medication can be added on a case-by-case basis. 

Can you prevent this from happening in your dog? 

Yes and no. Some infectious causes, for example parvovirus, distemper and tick carried diseases, can be prevented by routine vaccination and parasite treatment. Some causes affect certain breeds, such as pugs. But unfortunately, a lot of causes cannot be prevented. 

When should you see your vet? 

You should always see your vet if any neurological symptom develops. Neurological signs have many different causes and aren’t necessarily indicative of encephalitis. For example, seizures can also occur due to epilepsy and toxin exposure, so it is important we determine what exactly is going on so we can treat if possible or manage medically. Occasionally neurological signs can be a sign of something really bad going on in the brain, so early investigation and diagnosis is key. 

Conclusion 

Encephalitis, an inflammation of the brain, is a condition that can affect dogs of any age or breed, with both infectious and non-infectious causes. Infections can spread to the brain through various routes, such as the bloodstream or nearby tissues, but the non-infectious causes are a bit more complicated to identify. Immune-mediated encephalitis is not uncommon and involves the body attacking its own central nervous system. Symptoms can vary widely depending on the affected brain region, potentially including seizures, behavioural changes, coordination problems, and even systemic signs like vomiting. Diagnosis typically involves a combination of neurological examination, blood tests, imaging, and sometimes cerebrospinal fluid analysis to pinpoint the cause. Treatment varies based on the underlying issue, potentially involving antibiotics, immunosuppressants, and supportive medications. While some forms of encephalitis are preventable through vaccinations and regular veterinary care, many causes remain unavoidable. Therefore, recognising symptoms early and consulting a vet promptly is essential for your dog’s well-being.  

Further reading: 

Meningoencephalitis of Unknown Origin – Fitxpatrick Referrals 

Meningitis, Encephalitis, and Encephalomyelitis in Animals – MSD Vet Manual