Warmer Weather – Newer Diseases for Pets in the UK?

Our world is warming – 97% of climate scientists agree that modern civilisation is driving climate change, leading to average global temperatures increasing to over 1.2°c above pre-industrial levels, and the chance of this reaching 1.5°c or higher looking increasingly likely. Many of us are familiar with the possible consequences of global warming, including rising sea levels, larger and more frequent storms, longer drier summers, flooding, wildfires, ecosystem destruction and more. However, one often overlooked consequence may be an increase in new and rarer diseases in humans and animals. Today we will detail some diseases of pets that might become more common in the UK as our climate warms, and how they might be treated or prevented.

Why Might Climate Change Lead to More Exotic Diseases in Humans and Animals?

The relationship between climate change and disease is incredibly complex and still being understood, so we will keep the detail brief here.

Primarily, a warmer world means a larger area for pathogens that thrive in hot environments but struggle in colder environments to inhabit. Diseases like dengue fever that historically could not survive outside tropical regions are spreading further north and south, even as far north as the UK.

Furthermore, as the climate changes, and temperature, rainfall and humidity are affected, ecosystems and environments that were once stable become disrupted. Humans, animals and plants, and their pathogens, will be forced to migrate to find resources, or escape extreme temperature and weather. This further drives the spread of disease into new areas.

Climate change will also lead to a change in the seasons – historically in the UK, we had warm summers and cold winters. These relative extremes meant that many pathogens that could cause disease in summer died in winter; tick-borne diseases are a good example of this. However, climate change is resulting in warmer winters in the UK, increasing the duration of time these diseases can infect pets and animals. Changes in weather can also spread disease – some pathogens thrive in wetter environments, like malaria (and its vector, the mosquito). A warmer climate leads to increased risk of heavy rainfall, rising sea levels and flooding, which allows these diseases to spread.

In a worst-case scenario, if climate change results in a disruption of society in various parts of the world, healthcare systems that previously kept disease at bay may also break down, leading to disease spreading unchecked.

Are There Other Causes?

Aside from direct climate change, other related and unrelated factors may increase the incidence of exotic diseases within the UK.

Encroachment into Habitats

As human civilisation spreads, it brings us into closer contact with wild animals and their diseases. Climate change resulting in animal migration also increases this contact, as mentioned above. Many of humanity’s diseases originate in animals, so closer contact may increase the risk of rarer or new disease in wildlife infecting humans and their pets. In fact, this is one hypothesis of the origin of the COVID-19 pandemic, and is well established as the root cause of the Ebola and SARS outbreaks of the last few decades.

Importation

In recent years (and particularly during the COVID-19 pandemic), many prospective pet owners in the UK have opted to import animals from abroad, either via charities or independently. This practice is controversial for many reasons, and one is the risk of importing animals with exotic diseases that can either cause harm to the individual animal, or be spread to pets and humans in the UK that have not travelled themselves. While some diseases can be screened for, it is not always mandatory. Furthermore, illegal importation (smuggling) of pets is also on the rise, and may worsen disease spread as these animals are unlikely to be tested before being smuggled.

Travel

Travelling with pets is a growing trend, with over 300,000 travelling in 2019. Despite Brexit making pet travel more complicated and expensive, these increased numbers may open pets up to infection while abroad, and bringing the diseases back to the UK. Certain diseases, such as rabies and tapeworms, must be prevented or tested for before or after travel, but the majority of exotic diseases have no specific measures.

Migration

As people migrate to the UK and bring their pets with them, the risk of introducing disease increases. Since Brexit, net migration to the UK has increased dramatically, increasing the overall risk of disease. Furthermore, migration from European countries (with similar climates thus similar diseases) has reduced in favour of immigration from countries like India, Pakistan and China (with different climates and different diseases) which opens the door to more “exotic” (to us!) diseases. In addition, given that climate change is a significant driver of migration, this trend (or at least the pressure on the UK to accept more immigrants) is likely to continue, and thus foreign-born pets that could harbour exotic diseases may enter the UK in increasing numbers.

Why Are These Diseases a Problem?

Disease is, obviously, not desired, but what makes these new diseases so much worse than those already within the UK?

Less Knowledge

Though some of these diseases new to the UK are well studied in their native countries, doctors and vets here may be unfamiliar with them. Medical workers are often trained for pattern recognition (for example: a cough is more likely to be the common cold than a rare fungal disease), but this can mean when more unusual disease do occur, they can be missed at first approach. This can delay diagnosis and treatment. Of course, the more they are encountered, the more familiar medical staff get with them.

Naïve Populations

Thanks to herd immunity and regular exposure, many of the diseases that were dangerous to humans or animals in the UK are no longer so. But this immunity was developed over hundreds of years (and much illness and even death), and a new disease we have little exposure to would be much more dangerous. The recent COVID-19 virus is a perfect example of this – initially the whole population was unprotected (naïve) and thus illness and death were much more likely. As time went on, the population became protected via natural and artificial (vaccinations) immunity, making COVID less dangerous for the average person. If a new disease is brought into the country, pets may have little protection in the same way, until herd immunity develops.

Becoming Endemic

Despite some control measures, many exotic diseases do reach the UK in low numbers. Thanks to good control measures, these outbreaks are often stamped out before they spread widely. However, should an exotic disease escape controls, it may become endemic. This means that it is circulating in a population at a constant level. Leptospirosis and Parvovirus are two examples that affect dogs. While endemic disease does not mean a pandemic-level number of cases, without active measures it is difficult to fully eradicate the disease. Rabies was once endemic in the UK, but was eradicated after decades of measures, and the UK keeps safeguards up to maintain a rabies-free status. Climate change may easily lead to isolated cases of rabies, or other diseases, spreading and becoming endemic.

Zoonotic Diseases

Many of these diseases are not just a concern for animal health, but human as well. As we will explain later, most of these diseases are zoonotic, meaning they can spread from animals to humans and cause disease. Some are even more severe in humans than in pets. This makes control of exotic diseases from abroad critical for human and animal health alike. Pets and farm animals are the most likely animals to cause zoonotic infections, due to the close contact humans have with them.

New and Exotic Diseases

We will now list some of the diseases that may soon, or already are, becoming more common in the UK, thanks to a warming climate and the other factors listed above.

Leishmania

Leishmania is a parasitic disease mainly affecting dogs, though can also infect cats and other mammals, including humans. It is spread by a sand fly that bites the victim (and from infected mothers to their puppies, and rarely other dog-dog contact e.g. bites, or via blood transfusion). The parasite enters the body and develops over months and years into a mature parasite – during this sub-clinical period, there are few to no symptoms.

Once disease develops, the symptoms vary wildly. Skin disease is common, including dermatitis, hair loss, ulceration, nodules, pustules and more. Leishmania can also affect the eyes, kidneys, bones, muscles and neurological system. It often causes weight loss and lethargy. The consequences of the disease can be fatal. Leishmania is zoonotic, and particularly dangerous for anyone with a weakened immune systems. Infected humans can have similar symptoms.

Leishmania can be diagnosed via testing of blood with specific tests, or biopsy of infected tissue. This can be difficult particularly in sub-clinical dogs. There is no permanent cure – treatment often requires lifelong medication to suppress symptoms, but dogs typically remain infectious and can spread the disease to others or relapse if treatment is stopped (or during other times of stress). Many of the treatments cause serious side effects, such as urine crystals. In some cases, euthanasia may be recommended to protect human health. There are licensed vaccines to prevent infection, but they are currently not widely used in the UK.

Currently, Leishmania and its sand fly vector is mostly found in central latitudes in Africa, South America and Asia, but are being found further north into Southern Europe. Individual cases are encountered worldwide mainly in dogs imported from warmer climates. The biggest worry of many in vets in the UK is that climate change may allow the sand fly to live comfortably in our climate, making Leishmania an endemic disease.

Babesia

Babesia is another group of parasites found in dogs and other mammals, including humans. However, it is spread by ticks that introduce the parasite when they feed on a victim. Some species are zoonotic, but currently there is no evidence that dogs can infect humans. The parasite damages the red blood cells, resulting in anaemia, yellow or pale gums, weight loss and lethargy. Sometimes neurological and respiratory symptoms can occur. It can be fatal. Some dogs will carry the disease with no symptoms.

Diagnosis involves viewing the parasite in the blood via a smear, or blood or DNA testing. It can be treated in cattle, but there are fewer drugs available for canine cases. Supportive treatment, including blood transfusions, may be required. Thankfully, it can be effectively prevented by ensuring your dog is protected against ticks, and avoiding areas where ticks are found.

Babesia was once only seen in UK dogs that had travelled abroad or been imported. However, we are starting to find cases of infection from dogs that have never travelled, and we now know that Babesia is present in UK ticks already (possibly introduced by travelling dogs carrying the ticks that escaped into the wild). As the climate warms, this parasite is likely to become more common and spread further north.

Lyme Disease

Lyme disease is another disease spread by ticks, this time a bacteria called Borrelia. Once more, it is found in many mammals, including dogs, cats and humans. The symptoms vary wildly, but in dogs are commonly intermittent lameness, lethargy, fever and inappetence. Rarely it can lead to kidney disease. Many dogs will have no symptoms either. In humans, a ‘bulls-eye’ rash is common in the early stages of disease. It can be diagnosed via blood testing, but can be difficult, with false-positive and false-negative results common.

Treatment requires a long course of antibiotics, and management of joint pain or renal disease. Once again, tick-prevention drugs will stop ticks feeding off your dog and spreading the bacteria. Some dogs can relapse. All ticks should be removed promptly without damaging the tick using a special tick-remover.

Unlike rarer diseases, Lyme disease has long been endemic within the UK, but the incidence appears to be increasing, with climate change likely playing a large part due to expansion of the tick-vector’s habitat range.

Other Tick-Borne Diseases

As well as Babesia and Lyme disease, there are a number of other similar diseases spread by ticks that are currently rare in the UK, but may also become more common with a warming world.

Ehrlichia is a bacteria infection that damages white blood cells, while the related Anaplasma damages platelets. Both result in generalised unwellness, lethargy, weight loss and changes to blood parameters. Rickettsia causes similar symptoms and also damages platelets, causing bruises to appear on the skin.

All can be diagnosed, with difficulty, in the same way as Lyme disease, and treated with similar antibiotics. Prevention is much simpler, and covering your dog with a tick-preventative should protect your dog if they are bitten by an infected tick.

Heartworm

Heartworm, Dirofilaria, is a serious disease affecting the heart of dogs, ferrets and cats. It is spread when an infected mosquito bites the animal. It does not infect humans. The larvae of the heartworm migrate to the heart and pulmonary vessels to develop. The effects on the pulmonary system result in a cough, difficulty breathing, lethargy, heart changes, coughing blood and even sudden death if the vessels rupture.

Diagnosing heartworm can be done by blood testing, but this can be hard as antigen testing only works when the larvae have matured around 7 months after infection. Changes related to heart and lung disease may be seen on x-ray or ultrasound, but these are not specific to heartworm. There are various treatments that kill heartworm, however treatment can be risky, as the dying worms can cause an immune reaction that can worsen symptoms or even prove fatal. Prevention via a good anti-parasiticide is crucial for dogs living in heartworm-endemic areas.

Heartworm is, again, not endemic in the UK, but more cases are being seen mainly in dogs that have been imported form or travelled to southern and eastern Europe. There is a strong likelihood, however, that the south of the country will soon be warm enough for mosquitoes and heartworm to flourish and infect more dogs.

Summary

As the world warms due to climate change, new and exotic diseases are more likely to infect pets and humans in the UK

Other factors, such as pet travel, animal importation and migration will also increase this risk

These diseases are dangerous due to less awareness and knowledge, a naïve population and zoonosis

Many of these diseases are spread by vectors, like ticks or mosquitoes

Some of the diseases have vague symptoms and can be fatal

Some are zoonotic and can infect humans too

Diagnosis of these diseases can be difficult. Treatment can also be difficult and not always successful

Preventing infection can sometimes be achieved via anti-parasiticides and avoidance

It is recommended to avoid importing pets from abroad, ensure any pets that travel are protected, and to check for which diseases are present in the country your pets are visiting.