Being a pet owner is about more than fun and cuddles. It is also about dealing with nasty situations and preventing diseases. Parasites are one of the major challenges that pet owners must face.

In the modern pet world, parasites are a hot topic. And that might have something to do with the increase in global temperatures.

Wait, how did we start talking about seasonal change when discussing parasites? Well, as weird as it may sound, these two topics are closely related.

Let us start with the basics.

A kitten - Siberian cat hunting in grass. Purebred, red color type

What is a parasite?

All living creatures are in a relationship with each other. There are many different forms of relationships. While some are beneficial to both parties, others can be detrimental or even life-threatening.

Parasitism is a particularly interesting form of relationship which in many can be detrimental or even life-threatening. It includes two organisms – a host and a parasite. The parasite lives either inside or on the host and basically exploits them. In a nutshell, the parasite is biologically adapted to consume the host’s resources in order to survive.

In basic terms, a parasite is an organism that lives at another organism’s expense and whose lifestyle can harm the exploited organism.
Based on where they live, there are two groups of parasites:

Endoparasites – parasites that live inside the host (as shown in the image below). Trichuris trichiura is an endoparasite that lives in the intestines.

Ectoparasites – parasites that live on the surface of the host.

whipworm (Trichuris trichiura) is parasitic helminthic nematode (roundworm) under the microscope view for education

Ectoparasites – the great risk

External parasites pose a great risk for our pets’ health. Their negative impact occurs on several levels and includes many detrimental effects.

External parasites can cause cutaneous (skin) lesions.

The skin lesions are a problem in themselves – for example, fleas make the skin itchy and sore. What’s more, once the skin barrier is disrupted (by the external parasite), secondary infections (of bacterial and fungal origin) and skin inflammations (dermatitis) are likely to occur and further aggravate the already bad situation.

External parasites can transmit pathogens.

Those pathogens are responsible for causing diseases scientifically known as vector-borne diseases (VBDs). Vector-borne diseases can be very serious or they can go unnoticed.

External parasites trigger immune responses.

During their activity on the host’s surface, some external parasites penetrate the skin thus causing damage. What is more, while doing so, fleas leave their saliva in the skin, which triggers an allergic reaction. The so-called flea allergy dermatitis is the most common example of an immune reaction triggered by an external parasite.

External parasites have zoonotic potential.

A pet infested with external parasites increases the risk of the owner acquiring those same external parasites. In such cases, just like the pet, the owner faces dangers – one associated with the parasite itself and the other with the pathogens the external parasite may carry within them.

External parasites can compromise the pets’ overall health.

External parasites, their immediate activity on the host and the potential pathogens they carry are all attacking the pet’s health and compromising its integrity.

Beagle dog scratching body on green grass outdoor in the yard .

Which external parasites are a risk for our pets?

Our dogs are endangered by two major groups of external parasites:

The sub-class Acari (includes ticks and mites)
The class Insecta (includes phlebotomes or sand flies, flies, mosquitoes, chewing and sucking lice).

Geographical distribution, ways of spreading and diseases

To defeat the enemy – in this case, external parasites – we must know everything about them. To this end, we will now review the most common external parasites in Europe. We will discuss their geographical distribution, ways of spreading and the diseases they transmit.


Ticks are a group of bloodsucking parasites that includes 12 different species. These are the most important tick species in Europe:

Ixodes ricinus – widely present across Europe, it is responsible for transmitting the pathogenic agents responsible for borreliosis (Lyme disease), neoehrlichiosis, anaplasmosis, Q fever, tularemia and European tick-borne encephalitis.

Rhipicephalus sanguineus – predominantly present in southern Europe but spreading. Responsible for diseases like babesiosis, hepatozoonosis, ehrlichiosis, anaplasmosis, Mediterranean Spotted Fever and tularemia.

Dermacentor reticulatus – widely distributed in Europe. Responsible for transmitting the agent that causes the most severe form of babesiosis in dogs.

Generally, tick infestations are seasonal and mark two peaks. The first peak starts in March and ends in June while the second pea starts in August and lasts until November. However, in certain regions tick seasons are longer and in some, for example in Spain, ticks are active all year round.


Fleas are wingless and blood-sucking little insects whose presence is particularly common among dogs, cats and small mammal pets.

In Europe, the most common flea species in pets are:

The cat flea – not very picky when it comes to choosing hosts. In fact, the cat flea is the most common flea in all pets.

The dog flea – this is much rarer, found in less than 10% of cases. Nonetheless, it poses a problem.

Fleas do not thrive in extremely hot, cold, dry and humid conditions and are not very fond of high altitudes. Therefore, it is safe to assume that fleas are distributed all across Europe with the exception of the Alps and Pyrenees.

Flea infestations tend to peak twice a year – in summer and in autumn. Nevertheless, since fleas can survive indoors, flea infestations are possible throughout the year.

Fleas spread easily among hosts. What is more, if the environmental conditions are right, the immature forms can survive for months without a host. This is particularly important because only 5% of the flea’s life stages (adulthood) is spent on the pets; they spend the remaining 95% (eggs, larvae, pupae) in the surroundings. Since a single flea can lay as many as 50 eggs per day, it is safe to assume that eliminating flea infestations from the environment can be even harder than from the host.

Fleas – or, more accurately, their saliva – trigger an allergic reaction known as flea allergy dermatitis. Heavy flea infestations can lead to significant blood losses as well as anemia (low red blood cell count), while, the cat and dog flea carry and can transmit tapeworms. Last but not least, fleas can transmit different pathogenic agents. For example, the cat flea carries bacteria responsible for causing cat scratch disease in humans.

Sucking and chewing lice

Lice are highly host-specific and wingless insects that come in two varieties:

Chewing lice – which feed on skin debris

Sucking lice – which feed on blood.

Heavy-chewing louse infestations cause skin lesions while heavy-sucking louse infestations can potentially cause anemia. Plus, some lice can carry and transmit tapeworms.

Phlebotomes or sand flies

The Phlebotomus sandfly is well-distributed in southern Europe, predominantly the Mediterranean region. It serves as a vector, transmitting the protozoan parasite (Leishmania infantum) responsible for causing leishmaniasis. Leishmaniasis is a serious and life-threatening disease that can affect dogs and humans.


With over 3500 species, mosquitoes are a nuisance found around the world. Mosquitoes are an important vector for two important worm types: one of them lives in the heart and blood vessels and the other under the skin.

Sarcoptic and notoedric mange mites

Sarcoptes scabiei is responsible for sarcoptic mange in many pet animals. The mite is widely distributed all over Europe but it is most frequently reported in urban areas in central Europe.

Sarcoptic mange is predominantly characterised by skin lesions. If left untreated the lesions can progress, culminating in life-threatening weakness and emaciation.

Demodectic mange mites

Demodectic mange mites are cigar-shaped, natural inhabitants of hair follicles. Unlike most external parasites, these mites are not contagious. However, they are opportunistic.

When the skin’s normal immune protection fails, they cause a condition called demodicosis. Canine demodicosis is caused by Demodex canis while feline demodicosis is caused by Demodex cati and Demodex gatoi.

Notoedres cati causes scabies in cats. It is easily transmissible and highly contagious. It can be found all across Europe.
N. cati causes notoedric mange characterised by hair loss lesions usually located on the head and the ears. Extremely heavy infestations debilitate the cat and may have fatal consequences.

Otodectic mange mites

The ear mite – Otodectes cynotis –causes ear inflammation in cats, dogs and ferrets. It is more frequently reported in youngsters than adults and in cats than dogs. The ear inflammation and its accompanying symptoms are medically termed otoacariasis.

Fur mites

Fur mites are relatively large, transparent and highly contagious parasites often seen as moveable, white dots among skin scales and dandruff. They usually infest dogs, cats and rabbits but if given the opportunity, they feed on humans as well.

Fur mites are largely distributed all over Europe. They transmit between hosts easily, through close contact. Fur mite infestations are particularly common among young pets.

Fur mite infestations are medically known by the term cheyletiellosis. So far, there are no pathogenic agents transmitted via fur mites. The only consequence of their parasitic lifestyle is localised skin inflammation which manifests inirritation and discomfort.

Harvest mites or chiggers

The chigger or so-called harvest mites are easily seen with the naked eye. It is an interesting fact that only the unusually orange-colored, larval form has parasitic features. They cause various skin lesions and hair loses.

Seasonal change affecting parasitic activity

How is seasonal change affecting parasitic activity?

Previously rare diseases or diseases endemic to tropical and subtropical areas are nowadays popping up worldwide. Things were much simpler in the past. We knew exactly which external parasites were expected and when. Today, external parasites – including those which were previously seasonal – are present all year round.

This is mainly because seasonal changes cause warmer conditions and warmer conditions equal longer parasitic activity and wider parasitic distribution.

The deeper effects of seasonal change on parasite distribution

Other reasons for the changing geographical distribution of external parasites are the increase of pet adoption and pet travel. When pets from endemic areas travel to non-endemic locations, they carry more than their passports. However, pet travels and adoptions do not significantly contribute to the problem on their own. For example, let us assume that an external parasite endemic to the Mediterranean region found its way into the northern parts of Central Europe. If the conditions are not favorable, that parasite would not be able to survive and invade future hosts. However, if the conditions are pleasant (warmer due to seasonal changes) the parasite will thrive.

Protect our dog from parasite

How can we protect our pets from parasites?

Looking directly at the problem, protecting our pets from external parasites has never been easier. Pet owners and veterinarians now have a range of products to use to control and prevent external parasite infestations.

On the flip side, if we look at the bigger picture, protecting our pets has never been more challenging. This is because external parasites are becoming an emerging problem in unusual places and in unusual times of the year.

The best way of protecting our pets is through proper education and use of anti-external parasite treatments on a regular basis – all year round if needed. Ask your vet for the protection that your pet needs.


Ever heard of the old African proverb – ‘it takes a village to raise a child?’ Well, the same concept applies to pets. Raising healthy pets takes combined efforts. Veterinarians, physicians and pet owners must work together to protect pets from the constantly increasing parasite-related risks. All people must work together to prevent or at least reduce the complications associated with warmer weathers.