It is perhaps still a misconception that dogs do not need to be wormed, or perhaps not wormed as frequently, during the winter months. However, we should not forget the potential zoonotic element and risk associated with certain dog parasites; that is that certain worms can be transmitted and cause disease in humans.
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Which worms can affect humans?
Toxocariasis is perhaps the most well-known and publicised of these diseases, which may in humans, can cause a myriad of symptoms including coughing, liver enlargement and blindness. Furthermore, dogs can pick up worms from just about anywhere in their normal environment; including parks, the countryside and even their own gardens; and when infected with worms, may show a range of differing illnesses. Dogs can also pick up worms at any time of the year.
Doesn’t the cold weather kill the worms?
We see much milder winters more frequently these days in association with climate change. This brings about a failure of temperatures to either fall or stay low. Any perceived tendency of the cold weather to therefore “kill-off” worm eggs, really does not exist. As such, the myth that dogs should not be wormed in the winter is one that certainly needs challenging. Any worm egg burden and environmental contamination is unlikely to reduce to any significant level in the winter months. And as such, worming needs to remain a regular event throughout the calendar year.
Common worms found in dogs in the UK include roundworm, tapeworm, lungworm, and less frequently hookworm and whipworm. Foxes, increasingly seen in both urban and rural locations, may harbour many of these worm species and act as an uncontrolled and untreated “wild” reservoir of infection (about which, we can practically do very little).
Certain worm burdens are more frequently seen in certain population types, for example roundworms in pregnant dogs or young pups. Tapeworm infections may be more common in dogs which scavenge, or those (rural or farm) dogs eating raw meat. Conversely, lungworm seems to be a nationwide problem with infection being widespread, albeit perhaps more prevalent in certain regions of the country.
Worms and eggs are rarely ever seen in the dog’s faeces and microscopic examination (to detect eggs) is required to positively identify an infected dog.
How are worms picked up?
Puppies may acquire their roundworm burdens via their mother, early on in life. Adult dogs are at risk from environmental contamination where eggs can remain active, contaminating soil for years. Dogs become infected either when eating soil, or from grooming themselves (eggs having become adhered to their coats from the environment).
For lungworm, the parasite’s life cycle has an interesting intermediate host involving slugs and snails. Direct ingestion of these creatures (or their slime which has spread onto grass, toys or into water outside), are potential routes of infection for the dog.
Fleas can act as an intermediate host to one of the UK present tapeworm species. An animal may thereby become infected through simply grooming (if fleas are present in their coats). If a tapeworm infected flea is ingested in this manner, a tapeworm infection may therefore subsequently develop.
Related disease and symptoms
Most animals probably have some worms at some stage during their life. As mentioned above, the parasites are typically microscopic (whether adult worms or the egg offspring); this makes it almost impossible to determine whether your pet is infected. Furthermore, many pets are capable of remaining asymptomatic (not showing clinical symptoms or signs) since the parasites are well adapted to their host.
Other symptoms may include excessive hunger, a failure to thrive, lethargy, weight loss, a dull coat and gastrointestinal symptoms (vomiting, diarrhoea) with abdominal discomfort. A particularly heavy gastrointestinal worm burden in young dogs can also have potentially severe effects on intestinal motility and rarely, may serve to create a partial or full obstruction.
Lungworm infection may also present with respiratory symptoms such as laboured, difficult breathing, coughing and exercise intolerance. Although the pathophysiological mechanisms are still not fully understood, lungworm is also capable of causing diffuse, widespread systemic bleeding abnormalities.
So, when to worm?
Appropriate worming treatment protects not only the health of your pet and family, but also the wider public. It is, of course, the advisable and responsible action to regularly undertake.
Various well known professional veterinary organisations and animal welfare charities recommend that dogs are treated against worms at least 4 times a year. There does, however, exist rationale for worming more frequently to combat lungworm (which has been shown to become clinical in dogs within as little as 38-40 days). And to also minimise the transmission of roundworm on an ongoing basis.
Certain groups of dogs (such as pregnant or lactating bitches and puppies under 6 months of age), will need alternative and more frequent worming regimes. There may also exist some differences in the frequency of worming needed for dogs, dependent on lifestyle factors and geographical location.
It would be unusual for a single worming treatment to kill an entire worm burden in any one individual animal, although worm numbers will be reduced. Rather, more effective worm control is more likely to be achieved with repeated and regular worming treatments. It is also important to remember that a dog is able to pick up *new* worms rapidly from the environment (as a reinfestation), following a previously successful treatment course. This highlights the need for ongoing active parasite treatment throughout the year.
And which products to use?
Now, more than ever before, there exists a myriad of safe, easily administered, parasite treatment options on the veterinary market. The use of veterinary licensed, prescription only products, obtained through your veterinary practice, provides an effective treatment choice. Whether you desire to use a topical spot-on product and/or oral medication, your vet is best placed to discuss treatment options. They will help you to choose the most suitable product for your individual pet. Lifestyle factors, breed and location within the country, will all influence the decision to be made.
However… As a profession, we are increasingly aware of the threat that wormers pose to the environment. So the most suitable drugs should be used rather than a more random “shotgun” approach. This is why we strongly recommend using prescription-medications (which are usually more effective and so fewer drugs need to be given), and always under the direction of your vet.
Other important points…
It is of course also always important to remember to pick up after your dog and dispose of faeces waste responsibly; thereby reducing the environmental worm burden and associated load. Removing the worms and their eggs, as well as any left over wormer, along with the faeces and putting them into appropriate bins for destruction is always vital!