Veterinarians must be knowledgeable about vector-borne disease and provide appropriate screening according to guidelines and recommendations from organisations such as ESCCAP and LeishVet to detect problems as soon as possible and as a result, improve patient prognosis. Globally, pet owners should also be encouraged to request comprehensive screening for any animals returning from Europe to other countries, too. This is important because many CVBDs present with diverse, non-specific signs or no clinical signs at all, making a definitive diagnosis challenging.

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5 Vector-Borne Diseases to Keep on the Radar

Here are five common CVBDs to increase screening for:

1. Ehrlichiosis

E. canis is the main Ehrlichia species found in European dogs. European countries bordering the Mediterranean Sea and the Balkans are endemic for the pathogen, and E. canis has also been detected in non-endemic countries north of the Mediterranean such as Switzerland and Germany. The E. canis vector is the Rhipicephalus sanguineus tick, also known as the brown dog tick, and the pathogen targets canine monocytes, producing initial clinical signs such as fever, dyspnoea and splenomegaly. Commonly observed laboratory abnormalities are anaemia, thrombocytopenia, serum protein changes and increased CRP and UPC. Dogs who are persistently infected can enter a subclinical stage for months or years, and in some cases, systemic disease involving bone marrow suppression and pancytopenia can occur. Due to its non-specific clinical signs, long incubation time and disease-course, it has been called "the silent killer".

2. Anaplasmosis

Anaplasma species identified in Europe include:

• Anaplasma phagocytophilum: This is found most commonly in Northern and Central Europe. It is transmitted by the sheep tick, also known as Ixodes ricinus, and causes granulocytic anaplasmosis. Signs are usually non-specific and can include fever, muscle and joint pain, thrombocytopenia, elevated liver enzymes and increased CRP.
• Anaplasma platys: This has been identified in similar European regions to E. canis. It is also transmitted by the brown dog tick and causes infectious canine cyclic thrombocytopenia. Dogs can be subclinically infected; in Europe, patients with severe, treatment refractory disease and various coinfections have also been recognised.

3. Lyme Disease

Borrelia burgdorferi is most commonly diagnosed in Northern and Eastern Europe. The tick vector Ixodes ricinus transmits the agent, with the potential to cause signs such as fever, polyarthritis, glomerulopathy, and in rare cases, cardiac dysfunction. If not diagnosed and treated appropriately, the infection can last months to years.

4. Heartworms

Dirofilaria immitis, which has historically been endemic in southern areas of Europe, is now extending northeast to regions such as Hungary and Slovakia where previously only isolated or imported cases were reported. Heartworms are transmitted by multiple mosquito species, causing pulmonary endarteritis that can chronically lead to pulmonary hypertension and right-side congestive heart failure.

5. Leishmaniasis

Leishmania species infection is a widespread endemic disease in southern Europe that seems to be spreading into new regions. Pet travel and the increased import of dogs through welfare organisations has led to high numbers of infected dogs in non-endemic countries and furthermore, the infection is being transmitted there without vectors (venereal, vertical, dog biting and blood transfusion). In endemic countries, disease is transmitted by female phlebotomine sand flies, and domestic dogs are considered the main reservoir. The pathogen causes a chronic systemic disease that leads to signs including weight loss, lethargy, non-regenerative anaemia and other laboratory abnormalities similar to ehrlichiosis, generalised lymphadenopathy, renal disorders (glomerulopathies are the main cause of death), onychogryphosis, arthropathies, ocular, gastrointestinal and/or skin lesions.

Co-Positivity

Dogs infected by multiple CVBDs are more likely to develop severe clinical signs and exhibit abnormal lab values, negatively impacting their prognosis. A 2022 European study demonstrated that co-positivity rates were significantly higher than expected for many CVBDs diagnosed. Co-infection with A. phagocytophilum and B. burgdorferi is common because they share a common vector – I. ricinus – and A. platys and E. canis are commonly diagnosed concurrently because they are transmitted by R. sanguineus. Co-infections can worsen some conditions and mask others, complicating diagnosis and treatment.

Screening for CVBD

The above-mentioned study (which represents the largest data set on CVBD seropositivity in Europe to date) showed increased number of tests as well as decreased test positivity over the study period. This may reflect changes in testing behaviour, potentially increased screening of healthy animals and increased implementation of effective preventative care.

As the awareness of CVBDs is increasing throughout Europe, comprehensive screening for tick-borne diseases caused by Anaplasma spp., B. burgdorferi, Ehrlichia spp., D. immitis, and Leishmania is relevant to catch disease and coinfections in the early stages, improving a patient's prognosis. Even with animals without obvious or only vague clinical signs, laboratory abnormalities (haematology, acute phase proteins/CRP or kidney markers as UPC/SDMA) can be present, pointing towards progression of infection toward disease.

Screening is especially important in areas with high prevalence and inadequate vector prophylaxis – as well as for travelling or imported animals.

ESCCAP (e.g. guidelines MG5) recommends routine tests for CVBDs that are prevalent and pose health risks to animals and control of infections through regular diagnostic testing in endemic areas. This acts to minimise risks for humans as well. LeishVet recommends serological screening of apparently healthy dogs living in or travelling to or from endemic areas as breeding dogs, dogs prior to Leishmania vaccination, imported dogs, dogs admitted for annual Leishmania health checks and blood donors; addition of PCR for donor dogs is applicable.

Early Detection for Longer Life

Vector-borne disease can cause debilitating and, in some cases, life-threatening illnesses for dogs. That said, including appropriate CVBD screening in your veterinary clinic can help you detect disease before the dog's condition becomes severe. In addition, these tests are important to identify co-infections that can potentiate disease pathogenesis and complicate treatment. Remember: Early detection for longer life.