Part Two: What are the risks?

The purpose of this part of our article is to provide you with some information regarding the parasites we routinely treat in veterinary medicine and consideration of any potential risks when not treating for them. As mentioned in Part One, parasite treatment is an area of veterinary medicine currently under heavy debate, with many people raising concerns regarding what impact the drugs we use to prevent parasite infestation may or may not be having on the wider environment.

We have aimed to provide you information about most common parasites we tend to treat for in the UK, along with a summary of the risks involved. We haven’t written this as a “quick read” but have tried to provide a fuller explanation into the challenges we need to consider when treating our pets. (However, a shorter summary can be found here or at the end of the article).

Fleas

The most common flea seen in cats and dogs is the “cat flea”. These fleas can be picked up outdoors and brought inside. Here they will merrily breed all year long, occasionally nibbling their human housemates while doing so (they often tend to have a favourite target!). Once established on our pets a female flea can lay up to 50 eggs a day. These eggs can then hatch in the environment as larvae which then like to find somewhere dark to hide. Here they form a pupae (like caterpillars). This pupal stage can last in the environment for up to a year before hatching out as an adult flea and starting the cycle all over again. When treating a pet for fleas, it is always important to remember to treat the household with a good quality house spray. It is also worth bearing in mind that even the best household treatments cannot kill the pupal stages and so once a flea problem has become established it can take some time to resolve!

What is the risk to your pet?

The main problem fleas pose to your pets is that they can be incredibly irritating, particularly if your pet is allergic to the flea’s saliva. Fleas are also part of the tapeworm lifecycle and some pets with fleas subsequently go on to develop tapeworm infestations. Additionally, over time a large flea burden can also cause an anaemia to develop in your pet. Fleas have been shown to carry bartonella, a species of bacteria that can cause “Cat Scratch Fever”.

Are they a risk to human health?

The most common concern clients have with flea infestation (other than seeing the fleas themselves!) is that family members have been receiving flea bites. However, there is also a disease that can be seen in people that is referred to as “Cat Scratch Fever”, and is caused by the infection of a bartonella species of bacteria. The bartonella bacteria can be transmitted via flea dirt in a variety of ways but the most common is via cat scratches. The symptoms of this disease in people are usually mild, but it can cause more serious complications in immunocompromised people. Due to the non-specific and often mild symptoms shown in people, it is hard to really know how commonly the disease is spread or its incidence within the UK.

What are the risks of not treating?

It is important not to ignore the risk of Cat Scratch Fever in households with immunocompromised people, however, the major concern with fleas to most of us is the annoyance factor of bites coupled with the length of time it could take to clear a household of infestation.

Who should consider treatment?

As mentioned, the cat flea is the most common culprit in UK households and so UK households with cats that go outside are more likely to encounter fleas. Many of us believe that dogs that live in cat free households are at lower risk of picking up fleas and so owners may consider not using preventative treatment. While this is probably true, there are no studies to confirm that this is the case. As such pet owners who chose not to treat should be aware that cat fleas can live quite happily on dogs and owners need to be aware of the challenges to treatment should their pet pick up fleas.

Roundworms

Dogs and cats tend to pick up roundworms by ingesting eggs from the environment including direct contact with other dogs; eating undercooked meat; or by eating other infected animals such as rodents, earthworms and birds. Once our pets are infected, the roundworm will complete its lifecycle, develop into adults, and start laying eggs of their own.

What is the risk to your pet?

Roundworms rarely cause significant disease in adult dogs and cats but infection can pass through the placenta and high worm burdens can cause significant disease in both puppies and kittens.

Are they a risk to human health?

Yes, but the incidence of infection is hard to know. The roundworms eggs can be picked up via contact with contaminated soil and sand; eating unwashed fruit and vegetables; or by placing contaminated objects in our mouths. Classic examples of environmental infection could be contact with contaminated fur and bedding or children playing in gardens or parks where infected dogs or cats have defecated.

Ingested eggs won’t develop into the adult stage in people, but can cause disease. Again, symptoms of the disease in people are normally mild but worms can develop to the larval stage and migrate to eyes, brain or liver. Children seem to be at more risk of this disease. Again, with the wide range of clinical symptoms and lack of routine surveillance, it is hard to know the exact incidence of this disease in the UK. It is thought that there are 1.4 billion people affected worldwide, and some studies have shown around 10.5 percent of people tested in European regions have been exposed at some stage. In addition, studies carried out in the UK have shown contamination in public parks all over the UK.

Who should consider treatment?

In the absence of regular worm egg counting, we would advise treating pets for roundworms at least 4 times a year. Households that are at greater risk such as those with children or whose pets are regular hunters should consider treating more regularly. It is also very important to help reduce environmental contamination by picking up faeces and disposing them promptly, both in the garden and in public areas. For those who do not wish to treat regularly, it is advisable to perform worm counts on your pets at least four times a year. Faecal egg counts can be performed either via your vet, or via a reliable commercial laboratory in which there is growing availability. But owners who chose this option need to be aware there is a chance their pet could become infected and shed eggs between tests.

Tapeworms

Both cats and dogs can pick up tapeworm in the UK. Cats tend to pick up tapeworm from hunting and ingesting fleas and lice; dogs can also pick up tapeworm from eating infected carcasses (sheep, cattle, pigs and other livestock) or raw food diets that have been inadequately frozen. Cats and dogs are considered the “definitive host” for these tapeworm species and as such the tapeworms will develop to full maturity and release eggs. However, other mammalian species are involved in the transmission. When the tapeworm eggs are picked up by these “intermediate” hosts (birds/sheep/cattle/pigs) they won’t develop into mature worms. Instead, the immature stage of the tapeworm moves to organs such as the liver and lungs of these species and form cystic disease.

What is the risk to your pet?

Tapeworms are rarely associated with significant clinical signs of disease in pets. Tapeworm segments leaving the anus may cause anal irritation. However, it should be noted that tapeworm does cause more significant disease in the “intermediate hosts”, wild birds in the case of cats, and livestock in the case of dogs. This can have significant welfare impacts to these animals as well as an economic impacts in farming areas.

Are they a risk to human health?

The dog tapeworm present in the UK, Echinococcus granulosus, can cause significant health concerns in people but this rarely occurs. Like the “intermediate hosts”, this tapeworm infection can cause cystic disease in multiple organs in infected people. This disease is seen more commonly in more tropical climates, but there is thought to be 10-20 new cases in the UK every year.

Who should consider treatment?

Owners of pets that regularly hunt or have access to carcasses or are on raw food diets should consider treating for tapeworm monthly. Owners of pets that have had a significant flea infestation should consider treating for tapeworm as well as fleas. Pets that receive regular flea treatment and have limited access to hunting or raw food diets are at much lower risk and require less regular treatment.

Travel Considerations

In addition to concerns about tapeworms currently present in the UK, it should be noted that there are also tapeworm species currently in mainland Europe that pose significant risk of ill health to owners. There are concerns in the veterinary industry that the current legislation with regards to travelling with your pet may not be adequate to prevent the importation of other tapeworm species. As such, in addition to your legal requirement to treat your pet prior to returning to the UK, we would also recommend repeating this treatment after you’ve returned to the UK to cover for any potential exposure to tapeworm between the day of treatment while away and your return to the UK.

Ticks

There are several species of tick widespread throughout the UK. These ticks are most often found in wooded areas or areas with long grass, especially in the spring, summer and autumn months. Ticks are multi-host parasites, in that they attach themselves to one host to feed, then drop off to go through a developmental stage before attaching to another host. Most ticks in the UK attach to 3 different hosts in their lifecycle. Whilst ticks can cause some discomfort and localised infection, especially if not removed correctly, the main health concern with ticks is the potential of spread of disease

What is the risk to your pet?

In the UK we have several diseases that can be spread to our pets and ourselves via tick bites. The most well-known one of these is Lyme disease. Lyme disease can infect dogs, humans, and more rarely cats, causing various problems including fever, lameness and kidney disease. The symptoms of the disease can be significant and prompt identification and treatment is vital. However, other diseases include anaplasmosis, babesia infection and tick-borne encephalitis.

Are they a risk to human health?

While people can pick-up tick-borne diseases, this would be due to a bite from a contaminated tick picked up in the same area as your dog found one, rather than transmission of disease from your dog. Lyme disease has been established in the UK for a long time and can cause a range of symptoms from mild fever through to paralysis if untreated. However, tick borne encephalitis is a relatively new arrival, having spread from mainland Europe, with only a few human cases being confirmed in the UK. It is a viral condition spread via tick bites that can cause a range of symptoms from mild flu-like symptoms up to meningitis. The virus has now been confirmed in ticks in Thetford Forest, Hampshire/Dorset Border, the New Forest and North Yorkshire Moors

Who should consider treatment?

We should consider regular treatment for pets that access areas that are more prone to ticks, such as long grass or wooded areas. Ticks are more prevalent in the spring, summer and autumn months. Regardless of whether you treat your pet or not, all owners should regularly check their pets for ticks and seek veterinary advice for the correct method of removing ticks using the recommended tools to assist. Cats seem to be less susceptible to tick disease than their canine counterparts. It is not clear if this may be because they are less prone to picking up ticks, or if they are better at removing them before we find them; but cats are certainly capable of picking them up, especially if they like to visit animal burrows.

Travel Considerations

There are many more disease risks associated with tick bites in pets that have travelled to mainland Europe than we have in the UK and we would strongly advise discussing any travel plans with your vet. There are no compulsory steps in the travel legislation that will protect your pet against tick borne disease while travelling and some of the tick species in Europe can be brought back to the UK to live quite happily in your household.

One of the European ticks that can carry a disease called babesia has been established in the UK for many years, but has not previously been known to carry the babesia infection. However, in 2015 and 2016 there were some confirmed cases of Babesia in the UK in dogs that had not travelled to Europe prompting concerns that it could become established here if given the opportunity. Prompt identification and management of the affected local area seems to have helped reduce its transmission, but it is still an area for concern.

Lungworm in Dogs

Lungworm is spread to dogs via the ingestion of infected slugs or snails or via toys or bowls that have come into contact with contaminated slugs and snails. Once infected, the larvae develop into worms which reside in the heart and major blood vessel of the lungs.

What is the risk to your pet?

Symptoms of lungworm are variable but can include breathing problems and pneumonia as well as bleeding and neurological disorders. Symptoms can be mild initially but can progress to fatal disease if not identified and treated.

Is there any risk to human health

No

Who should consider treatment?

We know that lungworm presence in the UK can be very patchy, with the disease being much more prevalent in some local areas compared to others. Dogs that like to eat slugs and snails are at more risk and should receive regular treatment, but we should be conscious of the risk to all dogs if they have toys or bowls that are left outdoors. It is an area where more information on local exposure would massively help our understanding of risks to individual households. However, the only route to discovering that information is by regularly testing the pets that have not been treated for disease.

What are the next steps?

Thank you for investing so much time in reading this article, we know this hasn’t been a quick read! The next step is to consider what risks your pet is exposed to on a day to day basis and discuss any concerns with our team at the clinic. As it is clear, there is no “one solution fits all” and we are always happy to individualise the treatment plan for your pet and your household depending on what you are concerned about. To help with the costs we have a well-established Pet Health Club. Our Pet Health Club can provide you with an individualised vaccination and parasite treatment plan as well as unlimited vet and nurse consults amongst other benefits to help provide the care your pet needs.

For more information on this or anything else discussed in either of these articles, please feel free to contact us at the clinic. Otherwise, we hope they have been helpful and thank you very much for your time.

(Summary table containing bite sized information on the article above)

Image 1: https://unsplash.com/photos/a-sheep-standing-on-a-lush-green-field-PvWLieySGsM

Image 2: https://unsplash.com/photos/brown-snail-in-rule-of-thirds-photography-SHpbGW-sSYE

As with any hotly debated issue, the online world is full of opinions. These opinions are often presented as facts that may not actually be true and can be coupled with advice that may or not be helpful. Advice such as recommending treating your pet with half doses of parasite treatments works just as well (a proven route to resistance to treatment!); or comparing flea infestations in our pets with lice infestations in our children (forgetting that head lice won’t infest are home and don’t carry diseases that some of the parasites our pets carry do!)

What we have aimed to in this two part article is try to give you a factual summary of how we have traditionally treated our pets and the challenges that impact our decision making, including prevalence of local disease. We will also look at what may be changing along with a better understanding of the risks and benefits that should be considered when choosing whether or not to treat our pets for these disease.

It’s not going to be a short story… (maybe sit down with a cup of tea) but we truly hope it will be helpful in clarifying the current and developing situation. This information is mainly considering the UK pet population and is a summary of where we are at in November 2024.

Where have we come from?: “Evidence based medicine” and “Do Least Harm”

Two of the tenants that form the foundation of responsible veterinary medicine are:

1. To make treatment plans based on all available evidence,
2. In the absence of sufficient evidence, to precede in a way that does the least harm.

One of the major challenges with deciding on appropriate parasite treatment protocols has always been the lack of definitive evidence on localised parasite risks. For example, we know Lyme disease, a disease transmitted by ticks, used to be mainly located in areas including the New Forest, the west coast of the UK and the highlands of Scotland. However, there is now evidence of it being found in tick populations throughout the UK, but little specific data of how prevalent it may be in any given area. We also know that lungworm has become established in the UK, especially in the south of England, but we don’t know how prevalent it is in local pockets around our local environment.

Given the serious health consequences of developing some of these parasitic diseases and the risk to human health in some circumstances, we as veterinary professionals and pet owners have traditionally decided the “least harm” route is to treat our pets with preventative treatment against these parasites to reduce the possibility of disease developing. This choice has been exacerbated by the fact it is usually cheaper for the owner to give preventative treatment to treat for parasites, than it is to test for the presence of the parasites themselves. Further to this, to make this treatment easier for most owners to give, companies have developed products that aim to treat all parasites in one tablet or spot on which can lead to over-treating for parasites that aren’t necessarily a concern for the individual animal.

What has changed?

The environment around us!

Again, the arguments around this area are heated and often contradictory. What we do know is that studies have shown a dramatic drop in the insect population within the UK along with a reduction in the biodiversity in our waterways. In addition, there are studies showing the level of drugs contained within some of the parasite treatments we use in the pet population have been found in our waterways (mainly fipronil and imidacloprid).

Now it is important to clarify that fipronil and imidacloprid have both been used in the agricultural industry for some time and this would have a significant impact on the levels found in waterways, but there is also evidence of these drugs present in waterways that were not near treated farms. A further study done in 2022 summarised that there was currently no clear evidence that parasiticides used in our pets were having a negative effect on the environment, but strongly stressed that this may be due to lack of evidence and called for in-depth regulatory investigation of the environmental risks of these drugs. A single study in 2017 also found moxidectin in waterways, and one Dutch study has shown evidence of flulaner in a water environment following a swim test with a dog that had been treated with that drug. Ultimately, a lot more research needs to be done to assess whether these drugs are truly having an impact on the environment.

We also need to see changes in the regulations surrounding what drug companies publish about their effects. While the use of parasiticides in agriculture are heavily regulated with regards to their environmental impact, there is less regulation regarding their use in pets. The argument being that the treatment of one dog or one cat has negligible effect on the environment, not taking into account the millions of pets being treated across the UK. This is something we believe needs to change.

So what to do next?

So while the cogs slowly turn in the regulatory bodies of the government and pharmaceutical industry, the question remains, what should we as pet owners be doing next?

Consider our individual household risk:

While the debate rages on as to whether and how much impact the use of parasite treatment used in the pet population has on the environment. It would seem prudent to reconsider the way we approach its use. We need to shift our thinking from simply “do least harm to the pet in our house” to also include “and do least harm to the environment around us” while also considering any potential health risk to the people living in our households and the local area.

However, this involves some difficult decisions and will ultimately come down to owners’ personal preference. There are risks that owners who chose to reduce their pet’s parasite prevention strategies should be aware of. Many of those risks are low, but again, it is an area that is hard to fill with absolute facts or figures.

With regards to discussing these risks, we have tried to summarise them as clearly as possible in Part Two of this article. Our goal has been to provide the information as clearly as possible, without being too alarmist! Our suggestion would be for you to read the information available, discuss it further on a one to one basis with your veterinary surgeon, and devise a parasite control strategy that you feel is best suited to your household.

Gather more information:

I suspect if you’ve read this far, you would agree that the most frustrating aspect of looking at the use of parasite treatments in pets is the persistent lack of information. We lack reliable information on:

• how many cases of human illness derived from pet parasites are seen in the UK every year;
• we lack data from the drugs companies about how these drugs are excreted into the environment and in what form (which they are currently under no legal obligation to research or provide);
• we don’t have enough information about the prevalence of these diseases in our local environment.

We are collectively trying to navigate a sensible solution to the treatment of our pets while dealing with some significant information gaps. Now some of these measures are out of our hands. We need a clearer national (human and pet) disease monitoring systems; we need legislation changes for the drug manufacturers to publish more information about how these drugs are excreted; and we need continued environmental research into whether the use of these drugs are impacting the environment and to what level. Monitoring of parasiticide levels in waterways are still on going, but as far as we are aware, there is no testing being done on soil.

Test not treat:

However, the only way we can learn more about the prevalence of disease in local area is by testing our pets. This will take a shift in the mindset of pet owners and veterinary professionals alike. For example, it has been far cheaper for us to treat for intestinal worms rather than to test for them, so that is what we have generally suggested, and what clients have happily embraced. Similarly, we know that lungworm tends to exist in pockets in local areas, but it is only by testing our patients and forming a database of where pets have been, that we can start to form a map of where those pockets are.

Ultimately, the cost of these tests would need to be borne by the pet owners themselves. In an environment where the costs of providing veterinary medicine have escalated heavily in the last 4 years, we appreciate that the discussion of increased costs for veterinary care won’t be welcome to many. However, it is worth looking at the UK horse population as a good example of how positive change can be achieved.

Twenty years ago, horses were routinely treated for intestinal worms, but horse owners often struggled with accurately weighing and dosing their horses correctly. This led to a situation where horses may have been treated too often and with dosages of medications that were too low. We know that under dosing of parasite treatment can lead to the development of resistance and we were certainly seeing a developing issue in the horse population at that time. However, the industry responded very well and there has been a clear shift from “regular worming treatments” to “regular worm egg counts”.

This has subsequently led to appropriate dosing only when necessary which is not only beneficial to the horses themselves, but also to the reduction of developing resistance. While we would need to be more careful replicating this system in the pet population as there is a greater risk to people that are exposed to eggs produced by intestinal worms from our pets than those from intestinal worms in horses, a switch to regular worm counts rather than medicating could be possible if done correctly.

In summary:

We need to consider making some major changes from funding of studies and regulatory changes from the government, right down to the way we discuss parasite treatment in our consult rooms and in our households with our pets. In the absence of concrete information, a lot of these decisions will come down to our personal assessment of risk. There are no right or wrong answers, but we would encourage you all to read the information provided, (avoid the misinformation found online!) then come and discuss your personal situation with a member of our vet team.

In mean time, please click here to find Part 2: What are the Risks?

1. https://unsplash.com/photos/brown-horse-on-green-grass-field-near-trees-during-daytime-pqX8m4ME5yw ↩︎