We are all linked, our well-being as humans is closely intertwined with the animals’ health and the environment’s health. Promoting one health while neglecting the other two does not end in positive results.

Co-existing with parasites and pathogens with zoonotic potential at times of remarkable seasonal changes is like skating on thin ice or chilling on top of a seemingly silent volcano – we are only seconds away from a disaster.

The Blue tongue outbreak in Central Europe in 2006, the recent bird flu and pig flu outbreaks, or even the most recent Covid-19 outbreak only prove the above-listed claim. We are all connected – domestic animals, wild animals, pets, and humans. To protect one, we must protect the rest. And proper protection always starts with formal education.

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Parasites, vector pathogens and zoonotic diseases

Parasites are a bewilderingly diverse group of organisms that occupy almost every existing habitat. Parasites invade humans, animals, and plants without being welcomed. They have efficient invasion and survival strategies.

A fascinating group of parasites is the group of external parasites or ectoparasites – parasites that live or eat on the surface of animals, pets, and humans. The direct harmful damage associated with external parasites involves blood loss, skin inflammation, myiasis, toxic and allergic reactions, and self-wounding

However, their indirect harmful damage is probably the most important, and it involves acting as a vector for many pathogens. Those pathogens can be protozoa, bacteria, viruses, tapeworms, or roundworms. External parasites can serve as mechanical (simply pick up the pathogen on themselves and transmit it upon contact) or biological (when the pathogen needs to spend some time inside the ectoparasite to complete its cycle) vectors. While the direct damage triggered by parasites is proportional to their abundance (the more external parasites in number, the more significant and more extensive the damage), the indirect damage is not proportionally dependent. Namely, a minimal number of infected vectors can cause considerable damage in terms of public health, economic losses, and overall welfare. What is even more dangerous, many of the pathogens transmitted through a vector, external parasites have zoonotic potential. A zoonosis is a disease that can be naturally transmitted between animals and humans. Each year, on a global level, over 300 000 people are exposed to zoonotic diseases.

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We evolve together

The first parasitic organism arose over 500 million years ago, and the first warm-blooded vertebrae appeared around 300 million years ago. That leaves a 200 million years long gap – a 200 million years-long head start in favor of parasites.

Therefore, when the first warm-blooded, terrestrial organism was born, several different parasites were roaming the earth and readily waiting for the opportunity to exploit the new resource. Before that, parasites used to feed on simple organic material, and now they are feeding on a warm-blooded host. Only one short evolutionary step forward and external parasites feed on pets and, through them, negatively affect us – modern humans.

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We live and grow together

During late Mesolithic and early Neolithic times, men domesticated and started breeding and farming livestock and companion animals. The human population continues to grow, causing increased urbanization on a global level.

The increase in human and animal populations works in favor of external parasites and their accompanying pathogens. The abundance of hosts results in more and more parasites.

For example, when host sources were scarce, a plethora of external parasites would die on their host searching quests. Now, with so many people and animals, the next potential host is just a hoop or a wing flap away.

External parasites owe their recent density expansion to two more factors. Firstly, through artificial selection and breeding, men decreased the animals’ resistance to certain external parasites. For example, thick furs made it hard for external parasites to reach the skin. By favoring individuals and breeds with shorter coats, we have made things easier for the external parasite. Secondly, by introducing animals to new regions, the man accidentally exposed them to endemic parasites against which the newcomers have no resistance at all.

Ultimately, our modern homes and houses are the perfect micro habitat for external parasites. The carefully controlled conditions (temperature, humidity, lighting) and constant supply of suitable hosts (pets and humans) allow external parasites not just to thrive but excel in places of the world where they would otherwise perish into nothingness.

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We face seasonal change together

When talking about seasonal change and rising temperatures we always imagine a concept that will become real in the future. Well, the future is here. Seasonal change is real and occurring and we must slow down the changes and learn how to adapt to the changes it will trigger.

But are we capable of adapting? The years of evolution have shown us that as a species we are capable of adapting but adaptation is a long-term process. So, the main question would be – can we adapt quickly enough? Well, our little parasitic enemy definitely can.

Female ticks can eat an amount of blood that is 250 times larger than their body weight. To achieve the same goal, a man would have to eat around a ton of food in just ten days. While engorging so much blood, the tick’s body enlarges from 3-4 millimeters in length to as much as 12-15 millimeters. To match this capacity, a man would have to increase his height to 5 meters. On the other hand, if the resources are scarce, ticks can starve for impressively long. In laboratory settings, unfed males, nymphs, and larvae have survived for ten years without food. The 2-3 millimeters long fleas can jump between 10 to 25 centimeters in length or height (the record for longest flea jump is 60 meters). To be worthy of comparison, a man would have to jump around 60 meters in length and 200 meters in height.

Comparing humans to ticks and fleas is like comparing apples to oranges. Our goal was to compare the ability to adapt and evolve new skills necessary for survival. In those terms, external parasites are definitely well-suited.

Even seasonal change favors their survival. First of all, external parasites are more likely to adapt to the negative impact seasonal changes may inflict upon them. Secondly, some consequences of seasonal change, such as the rise in temperatures actually have a positive effect on external parasites. Hotter temperatures mean longer parasitic activity and presence of certain parasites in otherwise unusual places. Last but not least, the seasonal changes and their accompanying weather extremes challenge our adaptation mechanisms and weaken our defense systems ultimately leaving us more susceptible to external parasites and vector-borne diseases.

All in all, the dramatic seasonal changes shifted the nature of the parasite to host relationships.

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We go through diseases together

As parasites become disturbingly present in more and more places, and for longer than expected, the risk of getting a vector-borne disease is increasing. Humans and pet animals are in constant risk.

Zoonotic diseases are an emerging yet frequently underestimated threat to global health. Today there are over 150 diseases with zoonotic potential. Some of them are newly evolved while others have existed but are becoming more frequent due to geographical expansions and humans invading animal territories (for example, deforestation) and getting into contact with bats and other wild animals.

On the other hand, we have vector-borne diseases that despite their lack of zoonotic potential are still affecting us by infecting our beloved pets.

At the moment, in Europe there are several key vector-borne diseases that due to seasonal change and the vectors’ massive distributions pose serious threat to pets.


Leishmaniosis is caused by the protozoa Leishmania infantum and transmitted by sandflies. The vector is widely distributed in Southern Europe. Leishmaniosis affects dogs, cats and humans in which it causes multiple organ failures or skin lesions.


Babesiosis or piroplasmosis is caused by protozoa from the Babesia family which are transmitted by certain ticks. Some tick species like Dermacentor reticulatus and Rhipicephalus sanguineus are distributed in western, southern and central Europe up to the Baltic. The parasite lives in red blood cells and causes severe anemia.


Dirofilariosis is caused by the worm Dirofilaria immitis and D. repens which is transmitted through mosquitoes distributed in southern and parts of central Europe. It affects dogs, cats and humans. The disease causes heart failure and blood vessel obstructions, or in the case of D. repens – worms living under the skin.


Ehrlichiosis is caused by the bacteria Ehrlichia canis which is transmitted via ticks. The vector is present in southern Europe and it affects dogs and cats. The disease is always linked with anemia.


Borreliosis or Lyme disease is caused by bacteria from the Borrelia burgdorferi group. The pathogen is transmitted via ticks. The vector is distributed throughout Europe. Lyme disease seldomly pets, but can be a serious disease in humans. It manifests with fever, rashes, muscle and joint issues and neurological disease.


Widely known as “cat scratch disease,” bartonellosis is caused by the bacterium Bartonella henselae. The bacterium’s main reservoir is the domestic cat and primary vector – the cat flea.The bacterium, the reservoir and the vector are distributed worldwide. Bartonellosis manifests mostly in immunosuppressed humans with fever, enlarged lymph nodes, and inflammations of the eyes, gingivae, and heart. This disease can have lethal consequences for some people.

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We fight together and protect each other

As already mentioned, education is the brick and mortar of a well-planned protection strategy. The key to education is held by veterinarians. Veterinarians are the main source of reliable information for pets worldwide.

What veterinarians do on a daily basis is noble and amazing, yet responsible and challenging. During these times of seasonal changes, constantly changing environmental factors and wider distribution of otherwise endemic vectors, veterinarians are facing an even bigger challenge. They are your pets’ first line of defense.

For that purpose, today, many vets create individually tailored protection plans for their patients. They make those protection plans based on several factors such as animal, lifestyle, season and locality.

Your trusted veterinarian’s guidance is essential. Consult on when and how to treat. It is of paramount importance to use these products correctly and responsibly.

Complex problems require complex solutions. Therefore, the right protection approach should be multidisciplinary, multimodal and holistic. Pet parents, veterinarians, governments – we must all join forces and work together.C

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There is an on-going, constant battle in which parasites evolve to become more efficient in their exploiting powers, vector-transmissible pathogens evolve to become more resourceful in finding vector-material parasites and hosts evolve to become more efficient in mitigating the negative effects of parasites and vector-transmitted pathogens.

History teaches us that evolution supports the best adapted. If this is true, an important question emerges – what are our odds at winning this battle against external parasites and vector-borne diseases? Are we capable of finding a way to co-exist with these creatures while protecting both ourselves and our pets from the risks they pose?

HistoryLuckily for us, our fate is not decided yet in the battle for survival. The advent of human science declared war on these tiny beasts. We can say that we are in the final round of the battle for survival right now – this is the deciding moment. At no point during history have there been so many external parasites and vector pathogens lurking. At the same time, at no point during history have we been so well informed on protecting us and our pets. At no point during history have we had so many efficient protection ways. teaches us that evolution supports the best adapted. If this is true, an important question emerges – what are our odds at winning this battle against external parasites and vector-borne diseases? Are we capable of finding a way to co-exist with these creatures while protecting both ourselves and our pets from the risks they pose?

External parasites are thriving due to seasonal changes, and vector-borne diseases spread as we speak. At the same time, seasonal change occurs as well. Bearing in mind the evolutionary skills parasites and their accompanying pathogens have, we know they are more than fit to survive in the future. The real question is – can we keep up? The answer is yes, as long as we join forces, we can keep up and survive.