Vectors: The Diseases They Transmit

Pathogens are disease-causing organisms which are spread from one animal – or host – to another by carriers such as fleas, ticks and mosquitoes. These little pests can be carriers of serious diseases which can affect our dogs and ourselves. When they bite and feed on a host – animal or human – they have the ability to transmit serious diseases. If you protect your animals from these parasitic organisms, you are reducing the possibility that they will spread these diseases and their risks.


Most ticks can feed on many kinds of mammals; some can also feed on amphibians, birds and reptiles too. Their eggs go through three life stages and they must have a blood meal at each stage in order to develop and survive.

When the tick bites, saliva from the tick enters the host, like mosquitoes. Disease can therefore enter the body and may be passed on to the host. The transmission of disease can take some time, depending on the different disease agents. Ticks may be attached to the host for several days as it takes in its blood meal. Any treatment intended to kill ticks must therefore work quickly enough to prevent the transmission of any disease.

Both movement and population growth in ticks have increased. The brown dog tick, for example, was once mostly found in the warm Mediterranean. It has now been found in Northern Europe. It is now able to survive in the colder months by living inside buildings. The Asian long-horned tick may have entered the U.S.A. in the ear-canal of dogs. Only one female tick is required to start a new population.


Mosquitoes need the protein in blood to create eggs. Only the females bite and suck blood; at the same time they secrete their saliva into the hosts’ bloodstream. They feed off many animals and humans and can pass any infection they may be carrying to these hosts.

Mosquito-borne diseases have increased because of mosquito population growth. These diseases are no longer restricted to areas once considered to be of high mosquito risk, such as tropical and subtropical regions; they can now be found around the world.


Although this is rarely found in SA, it does appear now and then in some regions. When a mosquito, infected with heartworm larvae, bites a dog, the heartworm (dirofilariasis) may enter the dog through the bite, starting an infection. These heartworm larvae develop into adults in the host animal’s heart and surrounding blood vessels. The mature heartworm reproduces and microfilaria (new infective stages of the worm) can enter the host’s bloodstream, where they can infect other mosquitoes when they feed. This may lead to heart and lung failure in the host. However, heartworms rarely infect humans.

Dirofilaria repens

These parasitic worms, transmitted by mosquitoes, live in the subcutaneous tissue of dogs. An infected dog may experience skin irritation, swelling and conjunctivitis in their eyes. However, most infections are asymptomatic. Humans may also contract Dirofilaria repens from mosquito bites, but most of these larvae die before maturity. Localised swelling may be the only symptom.


Female sandflies, like mosquitoes, need blood meals to produce their eggs. Sandflies are little gnats which breed in moist, dark places. Organic matter is required to feed them.


These organisms/bacteria, which can cause a variety of diseases, are transmitted by tick bites. They can cause infections in both dogs and humans and include organisms such as Ehrlichia and Anaplasma.

Diagnosing Vector-Borne Diseases

If your vet suspects that your dog has a vector-borne disease, he or she may take a blood smear and examine it through a microscope.

Some dogs may continue to test positive for years after infection – in Ehrlichia, for example – which makes it difficult for vets to diagnose a positive test as a recent infection or one that occurred in the past.

Preventative Measures

Treatments such as Bravecto® will effectively reduce the risk of your pet contracting the tick-borne disease for at least 12 weeks depending on which product you choose.

Regular visits to your vet and particularly if you notice any health changes in your pet, will help to ensure that any infection by parasites is picked up early and treated accordingly.


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