What’s Bugging Your Dog?

Most Common Dog Diseases Transmitted by Parasites


1 Oct, 2021

7 minutes

Most Common Dog Diseases Transmitted by Parasites

If you have a dog, then you probably agree that dogs are a breath of fresh air. They have a way of dragging you outside several times a day. Some days, it might be hard to tell who is walking whom — but we all agree that fresh air and sunshine can make any soul feel better. One important step is to make sure that, when you take your best friend outside, he or she is protected from little creatures that might want to bite or latch onto skin and fur because these teeny little bugs can wreak havoc with your world. They also transmit some nasty dog diseases. Changing weather patterns with warmer temperatures and milder winters are contributing to this risk by making it easier for disease-transmitting parasites to survive for more months of the year. Also, people are traveling more around the world with their dogs, picking up and moving diseases to new areas. Take a few moments to armor yourself with knowledge that can protect your furry friends, your family, and you.


Mosquitoes spread heartworm to dogs. Therefore, this dog disease tends to be common in areas with abundant mosquitos; as found in many parts of the world. Heartworm disease is caused by a parasitic worm that can infest any dog, regardless of age or sex, although adult worms take a few months to develop and are not found in very young dogs. Adult heartworms live in the dog’s blood particularly in its heart and adjacent blood vessels. They can grow from 4-12 inches in length, reach maturation one year after infection, and live for approximately 5-7 years. Adult heartworms release offspring, known as microfilariae, into the dog’s blood. When a female mosquito bites an infected animal, it sucks blood containing microfilariae, which then develop inside of the mosquito. They are then transmitted when the mosquito bites another dog.

Infected dogs may not show clinical signs in the early stages of the disease. Once the disease progresses and the adult worms have developed in the blood vessels, signs of heartworm disease can become apparent. Canine heartworm disease signs are not enough to make the diagnosis, and can include coughing, difficulty breathing, lethargy and fatigue, loss of appetite, and weight loss.

Heartworms in dogs are a life-threatening parasite. The earlier they are detected and treated, the better the chances that your dog will recover with fewer complications. Heartworms in dogs affect their heart by restricting blood flow and can cause damage to other internal organs. The heart may enlarge and become weakened from the increased workload, and heart failure can occur. If untreated, the disease can be fatal. Your veterinarian can run a quick blood test to detect if your dog has heartworms. Further tests, such as chest x-rays, bloodwork, and an ultrasound of the heart (echocardiogram), may be necessary to confirm the diagnosis, to evaluate the severity of the disease, to evaluate the disease progression in later stages, and to determine the best treatment plan for your dog.


Ticks spread the parasitic germ (protozoa) Babesia, which causes Babesiosis, to dogs. This parasite infects the dog’s red blood cells leading to lethargy, lack of appetite, fever, hemolytic anemia (where the dog’s red blood cells break down), jaundice (i.e., yellowing of the skin, also called icterus), and weight loss. Specific tests, including blood tests and careful examination of blood smears, are needed to confirm the diagnosis. The treatment can be intensive, and blood transfusions may be required.


Certain types of biting Sand flies transmit the protozoan parasite Leishmania to dogs. Leishmaniasis is a serious disease affecting much of Latin America and the Caribbean, Southern Europe, parts of North and East Africa, as well as the Middle East and Asia. In Italy, for example, the prevalence of this disease is estimated to affect over 17% or about 1.2 million domestic dogs.

Even if you don’t live in these areas but visit them with your dog, there is a risk of transmission. It’s important to know that Leishmaniasis is a zoonosis. This means that through the bite of the infected sand fly, you too can be affected. It is, therefore, a disease that can be transmitted to humans.

Leishmania affects the internal organs and skin of the dog. You may notice skin lesions, weight loss, tiredness, dandruff, loss of hair, abnormal growth of nails, a bleeding nose, or enlarged lymph nodes. Your vet will need to run specific diagnostic tests to confirm infection.

The good news is that it is possible to control Leishmaniasis with proper prevention: it is essential to protect healthy dogs from infection, as and to reduce disease spread from infected dogs to other dogs or even humans. The fight against the spread of the disease is based on two main factors: protection from the bite of the sand fly and vaccination.


Borreliosis, commonly referred to as Lyme disease, is a bacterial disease transmitted by deer ticks to dogs, cats, and humans. Symptoms include fever, loss of appetite, swollen and painful joints, and fatigue. It is important to note that symptoms may not develop for several months after a tick bite. People who are bitten by an infected tick may develop erythema migrans,  a spreading red rash that resembles a bull’s eye. This rash is not easily seen on animals.


Anaplasmosis is a bacterial disease that is transmitted in at least two forms with the scientific names: Anaplasma phagocytophilium and Anaplasma platys. Deer ticks and western black-legged ticks are ticks that can transmit Anaplasma phagocytophilium. This disease affects the white blood cells in dogs, cats, and humans. Fever, lethargy, loss of appetite, joint pain, and stiffness appear 1-2 weeks after infection. Anaplasma platys may be transmitted by the brown dog tick. This bacterial disease causes a decrease in platelet count in dogs, and sometimes cats. In addition to the clinical signs above, some animals may also suffer bruising and bleeding due to the decline in platelet count.


Ehrlichiosis is a bacterial disease transmitted to dogs, cats, and humans by a variety of ticks including the American dog tick, the brown dog tick, and the lone star tick. This disease causes flu-like signs — fever, fatigue, joint pain, vomiting, diarrhea — usually within one to three weeks of being bitten by an infected tick. Just as with Anaplasmosis, bleeding disorders can also occur in affected dogs.


Rocky Mountain Spotted Fever is a common disease in dogs caused by a bacteria with the scientific name Rickettsia rickettsii. It is transmitted to dogs by several different ticks including the American dog tick and Rocky Mountain wood tick. Humans can become infected from a tick bite or following contact with tick blood and lymph fluids or excretions during the removal of engorged ticks from their dogs or themselves. Symptoms develop within five to ten days after exposure. They include fever, loss of appetite, enlargement of lymph nodes, joint inflammation, coughing or difficulty breathing, abdominal pain, vomiting, diarrhea, and swelling of the face or extremities. In severe cases, flat, perfectly round purplish-red spots may be seen on the linings of the eyelids and mouth. These spots are caused by bleeding below the surface of the tissue. Signs of nervous system involvement, such as altered mental states and increased painful spinal sensitivity from a usually painless touch, may be seen. Between 1% and 5% of dogs with Rocky Mountain spotted fever die from the disease.


Tiny creatures can make a significant impact! This is why it’s so important to take the necessary precautions to protect your furry friend at all times. Talk to your veterinarian about ways to prevent the spread of dog diseases through mosquito, tick, and sandfly bites. Appropriate parasite control is vital and should be administered year-round to reduce the risk of infection that could cause serious harm.