Vector-borne diseases in dogs

Vector-borne diseases (VBDs) are diseases that are carried by vectors such as ticks, fleas, mosquitoes and sand-flies. A vector does not cause disease itself but can spread infection by passing on pathogens from one host to another. Due to climate change, increased pet travel, and imported (and rescued) dogs, these diseases are becoming more common.

©Glen Cousquer

A vector-borne disease (VBD) is a disease that is carried by a variety of vectors such as ticks, fleas, mosquitoes and sand-flies. Ticks are parasites that need blood to complete their development and do this by seeking a host and biting. This process can pass on pathogens which are infectious agents, eg bacteria, viruses and other micro-organisms such as protozoa which can pass on disease.

Lyme disease (also known as Borreliosis) is perhaps the most well-known vector-borne disease that affects humans. Caused by a bacterium (Borrelia burgdorferi), it is transmitted by Ixodes ticks (commonly known as sheep, deer or hedgehog ticks. It can also affect dogs and cats.

Ticks are blood-feeding parasites that spend variable times on their hosts. In the UK ticks are most active in spring, summer and autumn when they are searching and feeding on a suitable host, but can be encountered at any time of year.

• Ixodes ticks (commonly known as the deer, sheep tick) are the most important and common ticks in the UK. They can spread diseases such as borreliosis and anaplasmosis. Members of the Ixodes tick family include the sheep or deer tick (Ixodes ricinus), the hedgehog tick (Ixodes hexagonus) and the British dog or fox tick (Ixodes canisuga).
• Less common is Rhipicephalus sanguineus (Brown dog or kennel tick). This tick has been carried into the UK from dogs imported from southern Europe. The tick transmits the bacterium Ehrlichia canis which causes Ehrlichiosis. It cannot live outside in the UK because temperatures are currently not warm enough but can live in centrally heated homes if introduced by pets that have been imported or have travelled abroad.
• Dermacentor species include the ornate dog tick, ornate cow tick or marsh tick. These ticks are seen worldwide. Dermacentor reticulatus is found in a few parts of the UK including The Welsh coast, South West and South East England. Dermacentor variabilis (American dog tick) and Dermacentor andersonii (Rocky Mountain wood tick) are seen in southern Europe, North and South America, Africa, Thailand and Australia.
• Amblyomma americanum (Lone Star tick) is mainly seen in North America.

Ticks can pass on bacteria or protozoa. Dogs can be infected by the following vector-borne diseases:

• Anaplasmosis (Ixodes ticks)
• Babesiosis (Dermacentor ticks)
• Borreliosis (Ixodes ticks)
• Ehrlichiosis (Rhipicephalus sanguineus)
• Hepatozoonosis (Rhipicephalus sanguineus)
• Tick-borne encephalitis
• Tularemia (Dermacentor ticks, Amblyomma americanum).

Fleas can pass on Bartonellosis, tapeworm and the plague (Asia, Africa, North and South America). Mosquitoes can transmit a wide range of vector-borne diseases including cause heartworm disease, cutaneous dirofilariosis and West Nile Fever while sandflies can spread Leishmaniosis. Chagas disease is another disease that can be transmitted to dogs via a kissing bug (mostly in South and Central America).

Many dogs will not show any signs of infection, but some will be lethargic, have raised lymph nodes  and have a fever. This can happen sometime after the tick or flea bite so you may not connect the infection with a bite. Dogs may also develop anemia, but this depends on the type of tick involved.

If you notice a tick on your dog, you should safely remove it with a tick removal device and take it to your veterinarian for identification. Your veterinarian may take blood samples to confirm infection.

To prevent vector-borne diseases being brought into the UK, dogs and cats returning to or entering the UK from abroad are advised to have received veterinary treatment with a licensed acaricide between 24 and 48 hours before their arrival in UK.

Prevention is the best way to avoid vector-borne diseases. Your veterinarian will advise you on the best way to control fleas and ticks using long-lasting, spot-on treatments. They will advise examining your dog for ticks after they have been outside, especially during the spring and autumn months when ticks are most active. It is also important to know how to remove a tick correctly so that the whole tick is removed, and mouth parts or other parts of the tick aren’t left inside the dog.

Treatment of any vector-borne disease will depend on the pathogen identified. If a bacterial disease has been found, your veterinarian may recommend antibiotics.

Some diseases are zoonotic – that is they can be passed on from dog to owner. This normally occurs when people are bitten by the relevant vector but people who have problems with their immune system should be aware of the risk of any infections that their dog can share. This is especially important when importing dogs from overseas.