Laurie Anne Walden, DVM
Fleas don’t just cause itching. They also carry infectious diseases that can be contagious to people. Controlling fleas on your pets protects your whole family’s health.
Tapeworms are parasites that live in the intestines. They shed small body segments called proglottids that pass out of the host animal’s body in the feces. Tapeworm segments in the stool look like whitish rice grains.
Fleas transmit a type of tapeworm that commonly infects dogs and cats. Dogs and cats become infected by swallowing a flea. Tapeworms rarely cause significant disease in dogs and cats.
The dog and cat tapeworm that is carried by fleas, Dipylidium caninum, can also infect humans (usually children) who swallow a flea.
Bartonellosis (Cat Scratch Disease)
Bartonella species are bacteria that cause a variety of diseases in humans and other animals. Cat scratch disease and endocarditis (heart valve infection) are just 2 of the serious illnesses caused by Bartonella infection.
Fleas are the most common insect vector for Bartonella henselae, the species that causes cat scratch disease. Fleas can also carry other Bartonella species. Infected cats and dogs might or might not have any symptoms of infection.
Bartonellosis is a human health risk. Treating your cat with a cat-safe flea preventive reduces the risk of cat scratch disease for people in contact with your cat.
Rickettsiae are a group of bacteria responsible for diseases such as typhus and Rocky Mountain spotted fever. Rickettsiae are spread by arthropods, including fleas and ticks. The types of fleas that infest dogs and cats transmit Rickettsia typhi (which causes murine typhus) and Rickettsia felis. Both of these bacteria can also cause disease in people.[1,4]
Plague, including bubonic plague and the Black Death, is caused by infection with the bacterium Yersinia pestis. The Oriental rat flea (Xenopsylla cheopis) transmits the bacterium usually to rodents but sometimes to cats, dogs, other animals, and humans. Rat fleas in the western United States and other parts of the world still harbor Yersinia.
Cats infected with certain types of Mycoplasma bacteria develop anemia (low red blood cell count). Fleas are thought to be a source of infection for cats.
Fleas cause skin disease in animals that scratch or chew themselves to relieve the itch. Just a few fleas can set off intense itching in an animal with a flea allergy.
Because fleas feed on blood, animals with lots of fleas can develop anemia from blood loss. This anemia can be life threatening.
1. Fleas. Companion Animal Parasite Council website. https://capcvet.org/guidelines/fleas/. Updated September 19, 2017. Accessed May 7, 2019.
2. Bartonella infection (cat scratch disease, trench fever, and Carrión’s disease). Centers for Disease Control and Prevention website. https://www.cdc.gov/bartonella/index.html. Updated December 14, 2015. Accessed May 7, 2019.
3. Shaw SE. Flea-transmitted infections of cats and dogs. World Small Animal Veterinary Association World Congress Proceedings, 2008. Veterinary Information Network website. https://www.vin.com/doc/?id=3866578. Accessed May 7, 2019.
4. Little SE. Feline fleas and flea-borne disease (proceedings). DVM360 website. http://veterinarycalendar.dvm360.com/feline-fleas-and-flea-borne-disease-proceedings. Published April 1, 2010. Accessed May 7, 2019.
5. Lappin MR. Update on flea and tick associated diseases of cats. Vet Parasitol. 2018;254:26-29.
Photo of Oriental rat flea (Xenopsylla cheopis) by James Gathany, CDC
Laurie Anne Walden, DVM
Adult heartworms grow up to a foot long, block blood flow around the heart, and cause inflammation within blood vessels. The damage continues as long as the heartworms remain in the body.
Heartworm treatment protocols for dogs are designed to remove the worms while reducing the risk of treatment complications. No safe heartworm treatment exists for cats and ferrets. Your veterinarian can recommend appropriate heartworm preventives for your dog, cat, or ferret.
Heartworm infection is diagnosed with a blood test. Your veterinarian might confirm the diagnosis with another test before proceeding with treatment.
Other tests, like x-ray imaging, echocardiography (heart ultrasound), and other blood tests, are used to assess the extent of damage. The results can affect the treatment plan, so your veterinarian might recommend these tests even if your dog isn’t showing any symptoms of infection. Dogs with blood clotting problems or signs of heart disease need a full diagnostic workup before treatment starts.
Any activity that increases the heart rate and blood pressure can worsen the problems caused by heartworms. Dogs with heartworms need to stay as quiet as possible to limit the damage. Once treatment begins, pieces of dead worms can break off and lodge in small blood vessels, potentially causing serious problems and even death. Strict exercise restriction is the best way to reduce the risk.
The American Heartworm Society (AHS) recommends restricting activity from the time heartworms are diagnosed until 6 to 8 weeks after the last dose of heartworm treatment. Dogs should ideally stay indoors in a small area where they can’t run or jump. Some dogs need to be confined to a crate. They should go outdoors on a leash only long enough to pee and poop. Ask your veterinarian about the level of confinement your dog needs.
Before Killing the Heartworms
Before dogs begin receiving adulticide (medication that kills adult heartworms), they may need treatment for heartworm-related problems. They should receive a certain type of heartworm preventive to remove larvae, or immature worms, from the bloodstream. They also benefit from a monthlong course of doxycycline, an antibiotic, to eliminate a bacterium that lives inside heartworm cells. This bacterium is partly responsible for the inflammation that occurs when heartworms die.
The AHS recommends that dogs start adulticide treatment 2 months after receiving a heartworm diagnosis (30 days after the last dose of doxycycline). Dogs should have limited activity during these 2 months.
The only adulticide currently approved for use in the United States is melarsomine. This drug is given by injection in a veterinary hospital. Your dog may need to stay in the hospital for observation after a melarsomine injection.
The number and timing of injections may vary depending on the situation. The current AHS recommendation is to give a series of 3 injections: 1 injection followed by a 30-day wait, then 2 injections given 24 hours apart. Your veterinarian will suggest a protocol that’s appropriate for your own dog.
Complete exercise restriction is crucial during adulticide treatment and for several weeks after the last dose. Your veterinarian may also prescribe medications to reduce adverse effects of treatment.
Your dog can be retested for heartworms several months after the last melarsomine injection. The goal of treatment is to remove all stages of heartworms.
Protocols to manage heartworm infection without using melarsomine are sometimes called “slow-kill” treatments. These protocols consist of giving doxycycline for a month and beginning a specific type of heartworm preventive to remove larvae. Heartworms take from several months to a year or more to die with these protocols.
The disadvantage of slow-kill treatment is that it allows adult heartworms to remain in the body for much longer than with adulticide treatment. The worms continue to damage the heart and blood vessels during this time. For this reason, the AHS does not recommend this method as standard treatment. Dogs receiving slow-kill treatment should also have exercise restriction for as long as adult heartworms remain in the body.
The advantage of slow-kill treatment is that it costs much less than melarsomine. Slow-kill methods have been proposed for dogs that would otherwise go untreated or be euthanized, like those in shelters or in areas where melarsomine is not available. Slow-kill treatment also offers an option for dogs at high risk of complications from adulticide treatment.
For More Information
See these resources from the American Heartworm Society:
Battling Boredom: Tips for Surviving Cage Rest (PDF)
Heartworm Positive Dogs: What Happens if My Dog Tests Positive for Heartworms?
Heartworm Treatment Guidelines for the Pet Owner (PDF)
Photo by Ryan McGuire
Laurie Anne Walden, DVM
Roundworms are some of the most common internal parasites in dogs and cats. They can also infect humans. According to the Centers for Disease Control and Prevention (CDC), 13.9% of people in the United States have antibodies to roundworms, meaning they have been exposed to the parasite at some point in their lives.
How dogs and cats are infected
Almost all puppies are born with roundworms. The type of roundworm that most often infects dogs, Toxocara canis, transfers from a mother dog to unborn pups through the placenta. T canis can also pass to puppies through the mother’s milk. Infected animals excrete roundworm eggs in their stool, so dogs can be infected by eating feces or swallowing roundworm eggs in the environment. Dogs can also become infected by eating a small animal (like a rodent) that is carrying roundworms.
The most common roundworm in cats is Toxocara cati. Cats and kittens are usually infected by swallowing roundworm eggs in the environment or by eating an infected animal. T cati does not pass to unborn kittens through the mother’s placenta.
Ingested T canis and T cati eggs hatch into larvae in the intestines. The larvae migrate through body tissues to the lungs, are coughed up and swallowed, grow into adult worms in the intestines, and begin producing eggs that pass into the environment through the feces.
Roundworm larvae can remain dormant in body tissues of adult animals instead of maturing in the intestines. These arrested-development larvae can’t be detected by fecal tests for worm eggs because they don’t produce eggs. Dormant larvae in a pregnant dog can become active and move through the placenta to the pups. In other words, a female dog with a negative test for roundworms can pass roundworms to her puppies anyway.
Signs of infection
Infected animals often have no symptoms at all. Dogs and cats (especially puppies and kittens) with lots of roundworms may develop a potbelly, vomiting, diarrhea, weight loss, or dull coat. Heavily infected animals sometimes vomit worms, which look a bit like spaghetti noodles, or pass worms in the stool.
Treatment and prevention in pets
Young puppies and kittens should receive multiple doses of deworming medication. The Companion Animal Parasite Council recommends deworming puppies and kittens every 2 weeks starting at age 2 weeks for pups and 3 weeks for kittens, continuing until they are about 2 months old, and then beginning monthly parasite preventives. Many heartworm preventives also prevent roundworm infection.
To reduce the chance your pets will be infected, remove feces from the environment and try to keep them from eating rodents or other wild animals. Have your veterinarian regularly test your pets for parasites, and give them parasite preventives all year round.
Infection in humans
People can be infected by T canis or T cati if they ingest contaminated dirt or feces. Toxocara eggs can survive in the soil for years. Children and people who own dogs or cats have an increased risk of infection, says the CDC.
Many people with Toxocara infection don’t develop serious disease and have no symptoms. But T canis and T cati larvae can migrate through the bodies of humans, as they do in dogs and cats. Larvae that migrate to internal organs (such as the liver) damage these tissues, a disease process called visceral larval migrans or visceral toxocariasis. Symptoms depend on the organs affected. Sometimes larvae migrate to the eye, causing a disease known as ocular larval migrans or ocular toxocariasis. People with this condition may develop retinal inflammation and vision loss.
Prevention in humans
The CDC recommends these steps to prevent toxocariasis:
For more information
Ascarid (Companion Animal Parasite Council)
Cat Owners: Roundworms and Dog Owners: Roundworms (Pets and Parasites)
Toxocariasis FAQs (CDC)
Photo by Berkay Gumustekin
Laurie Anne Walden, DVM
Are you tempted to skip your pets' heartworm and flea medicines during the winter? Dogs and cats actually need parasite prevention all year round. Year-round parasite control for pets helps keep the whole family safe from parasite-transmitted disease.
Warm spells during the winter are common in North Carolina, so we can’t count on cold temperatures to suppress insects that carry disease. Mosquitoes, fleas, and ticks can also live through the winter in areas that are protected from the cold.
Heartworms are transmitted by mosquitoes. Mosquitoes become active when the temperature rises above about 50°F (which happens routinely in North Carolina during the winter). But occasional warm winter days aren’t the only reason pets need year-round heartworm prevention.
Heartworm preventives work by killing tiny heartworm larvae that are already in an animal’s bloodstream. These larvae came from mosquitoes that bit the animal in the past month or more. Skipping a month of heartworm prevention could mean that your dog isn’t protected from heartworm larvae that he was exposed to when it was warmer. The American Heartworm Society recommends giving heartworm preventives all year round.
Intestinal parasites (worms)
Some heartworm preventives also control intestinal parasites like hookworms and roundworms. These parasites can infect humans too. Giving parasite prevention to your pets throughout the year is a sensible safety measure.
Fleas don’t just causing itching. They also transmit diseases like cat scratch disease, tapeworms, and plague.
Fleas lay eggs that drop off the infested animal into the environment. This means that flea eggs are present everywhere the animal has been, including inside a home. After the eggs hatch, the larvae and pupae (intermediate stages) can stay dormant for weeks to months before becoming adult fleas.
Because fleas can go through their life cycle indoors, they don’t need to wait for warm weather to develop into adult fleas. Flea infestations are easier to prevent than to treat, so the best chance of avoiding a flea problem is to give your pets year-round flea prevention.
Ticks carry many diseases that affect both pets and people. Some tick species, including the type that transmits Lyme disease, are active during the winter when the temperature is above freezing.
Ticks tend to live in leaf litter, crevices of buildings, and underbrush. When they’re ready to take a blood meal, they move to grassy areas or shrubbery near paths and latch onto a passing animal or person.
Ticks can be hard to see through fur, so you might not realize that your dog has picked up a tick. Because of the risk of serious disease, the safest approach is to limit tick exposure: control ticks around your home and give your pets tick preventives recommended by your veterinarian.
Photo by Justin Veenema
Laurie Anne Walden, DVM
Zoonotic diseases, or zoonoses, are infections spread from animals to people (and vice versa). Many zoonotic diseases are transmitted by insects, wildlife, and livestock, and some are carried by pets.
Controlling zoonotic disease is a cornerstone of One Health, the concept that human health, animal health, and the environment are all linked. July 6 is World Zoonoses Day and is also the anniversary of the day Louis Pasteur administered the first successful rabies vaccination to a person (July 6, 1885).
How to reduce your risk
Preventive care for pets helps keep everyone in the family safe. The chance of contracting a zoonotic disease from a dog or cat is low if you take proper precautions. Zoonotic infections are also spread by contaminated food, insects, ticks, farm animals, birds, reptiles, and rodents. Young children, older adults, and people with compromised immune systems are at higher risk than others.
These measures can lower your risk:
Find out more at the Centers for Disease Control and Prevention (CDC) website.
Zoonoses in companion animals
Many zoonotic diseases have been identified, and the CDC estimates that 75% of emerging infectious diseases originated in animals (often insects). Some of the most common zoonotic diseases in companion animals are listed below.
Other infectious agents
For more information:
Zoonotic diseases (CDC)
Zoonotic diseases and pets FAQ (American Veterinary Medical Association)
Photo by Lydia Torrey
Laurie Anne Walden, DVM
April is Heartworm Awareness Month. How much do you know about this infection? Check out the questions, then scroll down for the answers.
1. How are heartworms transmitted?
a. By mosquitoes
b. By eating raw meat
c. Through the feces of infected animals
d. By vampires
2. About how many dogs tested positive for heartworm in North Carolina in 2017?
3. Adult heartworms grow to what length in a dog’s heart?
a. 3 inches
b. 6 inches
c. 9 inches
d. 12 inches
4. In addition to dogs, which animals can get heartworms?
5. True or false: Dogs should receive heartworm preventives through the winter.
6. You forgot your dog’s monthly heartworm pill and now it’s a month overdue. What should you do?
a. Have your dog tested for heartworms before giving the pill.
b. Give your dog the pill now.
c. Give your dog a double dose.
7. True or false: Heartworm preventives sold over the counter at pet stores work just as well as the prescription versions.
c. Unfair trick question
8. Which state is free of heartworms?
d. None of the above
1. a. By mosquitoes
Mosquitoes pick up tiny heartworm larvae, called microfilariae, when they take a blood meal from an animal infected with adult heartworms. When the mosquito bites another animal, it injects these larvae into the new host. The larvae mature into adult heartworms in the new host in about 6 months.
2. c. 9000
According to the Companion Animal Parasite Council, 9457 dogs tested positive for heartworms in 2017 in North Carolina. This number has been increasing each year. To see more parasite statistics, see the Parasite Prevalence Maps on the Pets & Parasites website.
3. d. 12 inches
Adult heartworms grow about 12 inches long in dogs. Infected dogs typically have 14 to 20 of these foot-long worms in their heart and lungs.
4. c. Both
Both cats and ferrets get heartworm disease. In cats, heartworms do not grow as large as they do in dogs and are usually fewer in number. However, heartworm infection can be devastating in cats, potentially causing severe respiratory disease or sudden death. In ferrets, even a single worm can cause serious illness because ferrets’ hearts are so small. Medical options for heartworm removal (like those used in dogs) cannot be used in cats and ferrets. Heartworm preventives are available for cats and ferrets.
5. a. True
For best protection, the American Heartworm Society recommends year-round heartworm prevention for all dogs, not just for dogs in southern states. Also, think of this: for several days this past February, the temperature in Charlotte was 75°F or higher. Do you want to risk your pet’s health by guessing what the mosquitoes here consider “winter”?
6. b. Give your dog the pill now.
But do not give a double dose! Have your dog tested 6 months after missing a pill. The test detects adult heartworms, not larvae, so the test result will not be positive until the larvae have had time to mature.
7. b or c. False; unfair trick question
All heartworm preventives approved by the Food and Drug Administration for use in dogs and cats are available only by prescription. Deworming medications that are available over the counter (without a prescription) either don’t prevent heartworms or are not approved by the Food and Drug Administration for use in dogs and cats.
8. d. None of the above
Heartworms have been diagnosed in all 50 states.
For more information, see the American Heartworm Society website.
Laurie Anne Walden, DVM
Hookworms are common in dogs and cats, especially young animals in warm climates. These parasites are also zoonotic: hookworms that infect dogs and cats can also infect people.
What are hookworms?
Hookworms are small parasitic worms that live in the intestines of host animals. Different hookworm species have different preferred hosts. Hookworm larvae can also infect other animals—accidental hosts—that they happen to come in contact with. The symptoms of infection depend on whether the infected animal is a preferred host or an accidental host.
Adult hookworms in the intestines lay eggs that are passed out of the body through feces. Once in the environment, the eggs hatch into larvae. Larvae enter a new host’s body by penetrating the skin. Preferred hosts can also be infected by swallowing hookworm larvae, such as by eating contaminated dirt. Puppies can be infected through their mother’s milk.
In preferred hosts, hookworm larvae migrate to the intestines, where they grow into adult worms that reproduce and lay eggs. In accidental hosts, hookworm larvae cause a local reaction where they have penetrated the skin, but they do not mature and reproduce.
Hookworm infection in dogs and cats
The hookworm species that most often infect dogs and cats are Ancylostoma caninum, Uncinaria stenocephala, Ancylostoma tubaeforme, and Ancylostoma braziliense. These worms attach to the lining of the intestines and feed on blood. Infection can cause anemia from blood loss, which can be fatal in young puppies and kittens carrying large numbers of worms.
Symptoms of hookworm infection in dogs and cats depend on the number of worms and the age, size, and overall health of the infected animal.
A number of effective, safe medications are available to treat hookworm infections in dogs and cats. Young animals with severe anemia may need blood transfusions.
Hookworm infection in people
Humans can be infected by dog and cat hookworms if they come in contact with larvae in the environment—for example, by walking barefoot on sand or soil contaminated with hookworm larvae. The larvae burrow into the skin, causing an itchy skin reaction called cutaneous larva migrans. The larvae live only a few weeks in humans, so the symptoms may resolve on their own (contact your health care provider if you have more questions).
Humans are the preferred hosts for 2 hookworm species: Ancylostoma duodenale and Necator americanus. These hookworms are a major source of human disease worldwide and were once common in the southeastern United States.
Because dog and cat hookworms cause serious disease in animals and are also a health risk for people, preventing hookworm infections in our pets is important for both animal and human health.
The Companion Animal Parasite Council recommends the following for dogs and cats:
The CDC recommends these steps to prevent zoonotic hookworm infections in people:
For more information
Hookworms (PDF from Worms & Germs Blog)
Hookworms – Dog Owners and Cat Owners (Companion Animal Parasite Council)
Zoonotic hookworm FAQs (CDC)
Photo by Andrew Pons
Laurie Anne Walden, DVM
You probably know that ticks carry Lyme disease. But did you know that ticks also transmit other diseases that can make your pet seriously ill?
People and pets get the same tick-transmitted diseases. These diseases are not directly contagious between humans and animals (you won't catch Lyme disease from an infected dog), but we are all exposed to the same ticks outdoors. And one recent study showed that people with pets were more likely than those without pets to find ticks on themselves.
Rocky Mountain spotted fever
According to the CDC, North Carolina has one of the highest rates of Rocky Mountain spotted fever (in humans) in the country. The disease is caused by a type of bacteria called rickettsia. It is usually transmitted from a tick to its host within a few hours of tick attachment.
Symptoms of Rocky Mountain spotted fever in dogs generally begin a few days to two weeks after transmission. Some of the signs in dogs are fever, loss of appetite, joint pain (lameness or stiff gait), vomiting, and bruising of the skin or gums. It is potentially fatal but can be treated with antibiotics.
Like Rocky Mountain spotted fever, ehrlichiosis is a rickettsial infection. The Companion Animal Parasite Council reports that in 2016, over 16,000 dogs in North Carolina had positive antibody tests for ehrlichiosis--that is, they had been exposed to the bacteria at some point in their lives.
The symptoms of ehrlichiosis in dogs and cats depend partly on the rickettsia species and are similar to those of Rocky Mountain spotted fever. Dogs can also be infected without showing any symptoms. This disease is also treated with antibiotics.
Lyme disease, also called borreliosis, is caused by Borrelia burgdorferi bacteria. It is not as common in North Carolina as Rocky Mountain spotted fever and ehrlichiosis, although dogs do test positive here. (These tests do not show where the exposure occurred; some dogs may been exposed elsewhere and then traveled here.) The Companion Animal Parasite Council warns that the disease is spreading and that North Carolina and other states bordering typical Lyme disease areas may start to see more cases.
Borrelia are transferred from tick to host a day or more after tick attachment. Symptoms of Lyme disease vary, although fever and lameness that shifts from one leg to another are typical. The symptoms can be similar to those of other tick-borne diseases. Some dogs have no signs of infection. This disease can affect the kidneys, heart, and nervous system and may be fatal.
Like the other bacterial tick-borne diseases, Lyme disease is treated with antibiotics. A vaccine is also available.
Some ticks produce a toxin that causes paralysis. The symptoms range from weakness (usually beginning in the rear legs) to a complete inability to move. In severe cases the patient can die from paralysis of the muscles that control breathing. Removing all ticks may be enough to cure the disease. However, some dogs require intensive treatment in the hospital.
Ticks carry many other known diseases, such as anaplasmosis, babesiosis, and tularemia, and probably some that have yet to be identified.
Because tick-borne diseases infect animals as well as people, dogs can act as sentinels for these types of diseases in humans. For instance, a CDC report published in 2011 showed that the incidence of Lyme disease in dogs could predict the risk of Lyme disease for humans in the same geographic area.
To learn more
Parasite prevalence maps (Pets & Parasites)
Tick removal (Centers for Disease Control and Prevention)
Ticks (Companion Animal Parasite Council) -- guidelines for controlling ticks on pets
August 3, 2017
Image credit: CDC/James Gathany
Laurie Anne Walden, DVM