Ticks are more than just blood-sucking parasites; they are also vectors for disease. There are more than 900 tick species worldwide, and about 25 species are major threats to human and animal health.1 Every year, ticks cause nearly 95% of all reported vector-borne diseases in the United States. They spread more diseases than any other blood-ingesting insects, which include mosquitoes, fleas, flies, and mites. Ticks are a central vector for the spread of infectious diseases that include Lyme disease, anaplasmosis, babesiosis, Rocky Mountain spotted fever, tularemia, and ehrlichiosis.2
What Is Ehrlichiosis?
Ehrlichiosis is a rare bacterial disease that can be transmitted to a cat by a feeding tick. The tick becomes infected with the bacterium after ingesting the blood of an infected host, which is passed on to the cat through the tick’s saliva during feeding. Once the bacterium is in the cat’s bloodstream, it infects their white blood cells, reproducing and spreading throughout the body and tissues. This can lead to other problems with the cat’s red blood cells, white blood cells, platelets, and organs. When this disease occurs in cats, it is known as feline mononuclear ehrlichiosis.
The bacterium causing ehrlichiosis is a form of rickettsial disease that can also infect the blood cells of dogs, humans, and various other warm-blooded animals. It is zoonotic, meaning it can be passed from an infected tick to a person during feeding, but a person cannot catch Ehrlichia directly from a dog, cat, or another animal.
What Are the Signs of Ehrlichiosis?
Clinical signs of ehrlichiosis in cats can vary and be non-specific, often mimicking other diseases and disorders. It can be difficult to diagnose because it is a rare disease in cats, so other issues must be ruled out first.
Common signs include:
Other possible clues that a cat has ehrlichiosis are fever, a swollen belly caused by an enlarged spleen, and nervous system abnormalities, such as meningitis and bleeding within brain tissues. As the disease progresses, the bone marrow produces fewer blood cells, leading to a decreased number of platelets, which are important for the clotting of blood. With fewer platelets, cats with ehrlichiosis may bleed abnormally, with bruises forming on their skin. Blood may also be visible in their urine and feces, or they can suffer from nosebleeds (epistaxis).
What Are the Causes of Ehrlichiosis?
A tick cycles through four stages in its lifetime: egg, larva, nymph, and adult. They also feed on different hosts during their life cycle. A host is an organism that provides nutrients to a parasite. Rodents, deer, foxes, and other wildlife commonly harbor ticks. Unfortunately, domesticated animals, including livestock, dogs, and cats, can also be hosts to ticks. The tick becomes infected after it bites an infected host and ingests blood containing the Ehrlichia bacterium. Essentially, the tick acts as a vector to transmit the disease from one animal to another.
Many different species of ticks can be found in the world, but it is not clear which species transmit ehrlichiosis to cats. Dogs can become infected with Ehrlichia canis through the bite of a brown dog tick, so it is possible that this tick species also causes the disease in cats. A related disease is sometimes found in cats residing in Africa, France, and the United States, but the exact tick species has not been definitively identified.
Ehrlichia bacteria can quickly be passed on to a cat after an infected tick begins feeding on the cat’s blood. It can occur in as little as 3 hours! The bacteria are strictly intracellular organisms, meaning they live entirely within the cat’s cells. They may be visible within the cells just a few short weeks after the tick feeds.
How Do I Care for a Cat With Ehrlichiosis?
The diagnosis of Ehrlichia is based on a combination of factors, including the cat’s history and clinical signs, the physical examination, and diagnostic testing. Bloodwork is crucial for determining how well the cat’s organs are functioning and if any changes can direct the veterinarian toward specific diseases or conditions. A cat infected with ehrlichiosis may show bloodwork changes such as anemia, low platelets, and an increased monocyte count, which is a type of white blood cell that fights infection. A test that involves putting a drop of the cat’s blood on a slide and then examining it under a microscope can help the veterinarian determine if any bacteria are present within the cat’s white blood cells. Other tests, such as serology (which detects the presence of antibodies to the bacteria) and polymerase chain reaction (which finds bacterial DNA in the cat’s blood), are used to definitively diagnose ehrlichiosis in cats. However, these tests are non-specific for Ehrlichia and may detect other species of rickettsial infections, causing false positive or negative results.
If a cat is suspected to have ehrlichiosis or has been diagnosed with it, the treatment of choice is an antibiotic called doxycycline. The cat will take the antibiotic every day for at least 28 days (or longer, in severe cases) to completely rid themselves of the infection. The antibiotic is effective in most cats, and signs of improvement may be seen in as little as three days. However, some cats may not recover and either pass away or are humanely euthanized because of the severity of the disease. If a cat does not respond to doxycycline, the veterinarian should investigate other potential causes or prescribe an alternative antibiotic, such as tetracycline or imidocarb.
Cats with ehrlichiosis may benefit from supportive care if their clinical signs are bad enough. Those with little to no appetite may need supplemental feeding. Cats that have a fever, are dehydrated, or have vomiting and diarrhea may benefit from IV fluids. Joint pain can be managed with pain medications. Cats with anemia and other blood abnormalities may need blood transfusions to help them recover.
The prognosis for cats with ehrlichiosis is generally good, provided that they are treated appropriately. Blood work may be rechecked 1–2 months after successful treatment to ensure that the bacteria are no longer present. If a cat still has clinical signs and positive test results after the first round of treatment, another course of antibiotics may be needed. Long-term complications of ehrlichiosis include arthritis, eye problems, anemia, and possible side effects from blood transfusions.
Preventing ehrlichiosis consists of keeping your cat up to date on a tick preventative, avoiding tick exposure, and regularly checking your cat for ticks if your cat is allowed outdoors. If you find a tick on your cat, it should be safely removed as quickly as possible to lessen the chance of disease transmission. The Centers for Disease Control and Prevention has a great article demonstrating proper tick removal. If you are uncomfortable removing a tick from your cat, though, your veterinarian will be able to help you. Currently, there are no vaccines available for dogs or cats to prevent ehrlichiosis.
Can my cat use flea-and-tick prevention meant for dogs?
No, cats should not use dog flea-and-tick medication. Many products meant for dogs contain pyrethrins, which are chemicals that are extremely toxic to cats and can lead to seizures or even death. Always read the directions carefully, and only use products that are specifically formulated for cats and kittens.
Do indoor-only cats need tick prevention?
Yes, indoor-only cats still need to be protected from ticks. Although they are less likely to be infected, ticks can still be brought inside the house by outdoor pets or on your clothing. Year-round tick prevention for your cat is recommended in case one finds its way into your home unexpectedly.
Ticks can transmit ehrlichiosis to cats when feeding on their blood. The Ehrlichia bacterium affects the blood cells and bone marrow, which may lead to low numbers of red blood cells, white blood cells, and platelets. Doxycycline is the treatment of choice, and the prognosis is usually good for cats that are treated appropriately. The disease is zoonotic, so if your cat brings a tick into your home, there is a chance that the tick could transmit the disease to you when feeding on your blood. Therefore, your pets must be current on their tick prevention. There are several prescription products on the market, and your veterinarian can help you choose the best one for your cat.
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