When it comes to protecting animal and public health, regular screenings for CVBD are integral to preventing the spread of disease and monitoring infected dogs. Here's what you need to know about CVBD prevalence, coinfection, and how to stay on top of detection.

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Common Pathogens

In many EU countries, a complex tapestry of vector-borne pathogens capable of causing vector-borne disease in dogs is present.

Tick-Borne Pathogens

A wide range of tick-borne pathogens are present in Europe:

• Babesia canis
• Ixodes ticks transmitting Borrelia spp. (the cause of Lyme disease), Anaplasma spp., and tick-borne encephalitis virus
• Rhipicephalus sanguineus is common throughout Southern and parts of Eastern Europe and its range is spreading as the climate warms. Its ability to persist in centrally heated homes presents the opportunity for temporary foci to develop if pets move ticks to non-endemic areas. R. sanguineus can transmit Ehrlichia canis, Hepatozoon canis, Babesia vogeli, Anaplasma platys, and a range of Rickettsia spp.

Leishmania spp.

Transmitted by sandfly vectors and endemic in Southern Europe, seasonally in parts of Eastern Europe, and in the South of France, leishmania's range is extending as climate allows the spread of sandflies. It's also frequently seen in dogs who have travelled from non-endemic countries. Additionally, non-vectorial modes of transmission such as vertical and congenital routes as well as blood transfusion mean transmission is possible in sandfly-free areas. Early diagnosis of infected animals is vital in limiting vector-borne disease spread.

Fly-Borne Nematodes

Mosquitoes capable of transmitting both Dirofilaria immitis (heartworm) and Dirofilaria repens (subcutaneous worm) are present throughout Europe. Temperature, however, is a limiting factor for D. immitis spread as it requires a minimum temperature to complete its lifecycle in the mosquito. This has limited its range to Southern Europe, the South of France, and parts of Eastern Europe, but climate change is allowing it to spread steadily northwards. D. repens has a much wider distribution. The eye worm Thelazia callipaeda is transmitted by fruit flies and has seen its distribution rapidly spread across Europe. Climate change has allowed the geographical expansion of its fruit fly vector.

Coinfection With Vector-Borne Disease

These pathogens are often not encountered in isolation but with one or more coinfections. It can be easy to assume the cause of the presenting clinical signs is the result of a singularly diagnosed pathogen. Same with the diagnosis of a pathogen carried by a healthy patient. However, coinfections are common for a variety of reasons.

Common Vectors

A range of mosquito species can transmit both D. repens and D. immitis, making coinfection of these diseases common in endemic countries. Similarly, R. sanguineus is a tick capable of transmitting a wide range of pathogens including E. canis , A. platys and Babesia vogeli.

Common Risk Factors

Factors that increase the risk of mosquito infection such as outdoor activity, particularly at dawn and dusk, also increase the risk of sandfly exposure. This makes coinfections with Dirofilaria spp. and Leishmania more likely. Similarly, outdoor activity in tick-dense areas will lead to exposure to a variety of tick species leading to the potential for multiple tick-borne pathogen transmission.

Some Infections Make Coinfection More Likely

There is some evidence to suggest that Leishmania infections make coinfections with other parasites such as heartworm and tick-borne protozoa more likely. E. canis infection may also make hosts more susceptible to Leishmania infection.

Geographic Overlap

As the range of CVBDs grows, fuelled by changes in climate and land use in the face of increasing movement of both pets and humans, the likelihood of multiple vector-borne pathogens being present in a region also increases.

It is vitally important to consider the presence of coinfections in clinical cases, and subclinical patients be screened. Screening for coinfections will help to enable long-term clinical planning for infected patients as well as allow measures to be put in place to minimise the risks of onward transmission and zoonotic exposure.

Detection Is a Multistep Process

Vigilance for coinfections and canine vector-borne diseases as a whole requires several steps:

A Full Clinical Examination

Clinical examination may lead to direct visualisation of parasites such as T. callipaeda worms during an ocular exam. It may also reveal the presence of vectors such as ticks and fleas. The presence of vectors in dogs will indicate possible pathogens that may have been transmitted.

Biochemistry, Haematology, and Urinalysis

Changes in biochemistry, haematology, and urine can indicate certain parasites are present—individually or as part of a coinfection. For example, anaemias and thrombocytopenia may indicate the presence of tick-borne pathogens and Leishmania. Proteinuria is also an important prognostic indicator for Leishmania and may indicate its presence.

Testing for Specific Vector-Borne Pathogens

Testing is vital to establish which vector-borne pathogens are present in clinically affected patients and to confirm healthy animals are pathogen-free. Dogs should be tested annually for key pathogens so infections can be monitored, treatment initiated early where appropriate, and a long-term management plan put in place. New infections in a region or country can also be detected, forming a vital part of pathogen surveillance. Dogs relocated from one region to another should also be tested to establish which novel pathogens they may carry. This, in addition to individual patient management, will allow the risks of establishment and spread to be minimised.

Annual CVBD screening and the screening of relocated dogs are vital tools for minimising the spread of CVBDs and reducing the risk of coinfection. By implementing regular screening programs, veterinarians can play a crucial role in national biosecurity and surveillance while also protecting the health of pets and humans alike.

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