Feline Infectious Anemia (Hemotropic Mycoplasma): Signs and Treatment

What causes it

Three hemoplasma species infect cats, and they differ a lot in how much harm they do. Mycoplasma haemofelis is the most dangerous. It can cause severe anemia even in a cat that was healthy before. Candidatus Mycoplasma haemominutum is the most common species and rarely causes illness on its own. Candidatus Mycoplasma turicensis is less common and usually mild.

The two milder species tend to cause anemia only when something else has weakened the cat. Feline leukemia virus (FeLV), feline immunodeficiency virus (FIV), another illness, or medicine that suppresses the immune system can all make illness more likely. A cat can also carry more than one species at the same time.

These infections are found in cats worldwide, including across Europe. Studies show that cats with outdoor access, male cats, older cats, and cats with FIV or FeLV are infected more often.

How cats catch it

The exact route in everyday life is still not fully proven. Fighting is the main suspect. Traces of the bacteria have been found in the saliva, on the gums and on the claws of infected cats, so bites and deep scratches are a likely way in. This fits with outdoor male cats being at higher risk.

Blood transfusions can pass the infection on, and so can needles or surgical equipment that are not sterile. For this reason, cats that donate blood should be screened first. Passing from mother to kittens has been reported, but it has not been fully proven.

Fleas were long blamed for spreading the disease, and many older sources still say so. Recent research suggests that fleas play a small role at most. Regular flea control is still worth keeping up, because heavy flea burdens can cause anemia on their own, especially in kittens.

Signs to watch for

Signs depend on which species is involved and how fast the anemia develops. Owners often notice a quiet, tired cat first. These are the most common signs.

• Pale pink, white or grayish gums
• Tiredness and weakness, sleeping more than usual, hiding
• Poor appetite and weight loss
• Fast breathing or a fast heartbeat, even at rest
• A fever that comes and goes
• Dehydration
• Yellow gums, skin or eyes (jaundice), which is less common

Healthy gums are pink. To check, gently lift your cat's upper lip in good daylight. Some cats have dark patches on the gums, so look at the pink areas. It helps to know your cat's normal gum color before anything goes wrong.

Some cats have ups and downs. The number of bacteria in the blood can rise and fall sharply for several months after infection, so a cat may seem better and then slip back. Cats that carry the infection long term often show no signs at all.

When it is an emergency

Mycoplasma haemofelis can cause severe anemia quickly. Contact your vet or an emergency clinic right away if your cat has white or very pale gums, breathes fast or with an open mouth while resting, is too weak to stand, or collapses. A cat that stops eating and hides also needs to be seen soon, ideally the same day. Without treatment, about one in three cats with the acute illness may die, so prompt care matters.

How vets diagnose it

The vet will examine your cat, check the gums, heart and breathing, and feel the belly. The spleen is sometimes enlarged. Blood tests show how severe the anemia is and whether the bone marrow is making new red blood cells.

The bacteria can sometimes be seen on a blood smear under the microscope. This test misses many infections, because the number of organisms in the blood keeps changing. A PCR test, which detects the genetic material of the bacteria, is much more reliable and shows which species is present. Your vet may send a blood sample to a laboratory for it.

A positive result does not always explain the illness, since many healthy cats carry the milder species. Your vet will usually look for other causes of anemia as well. Testing for FeLV and FIV is common, because these viruses are linked to the infection and can make it more serious.

Treatment and recovery

Treatment is usually a course of antibiotics given by mouth for at least two weeks, sometimes longer. Your vet will choose the medicine and decide how long the course should last. It is best to give the full course exactly as prescribed, even if your cat seems better. Your vet may want to recheck the blood during and after treatment.

Cats with severe anemia may need to stay in the clinic. Supportive care can include oxygen, fluids and a blood transfusion. In one study, about a third of cats treated for this disease needed a transfusion. Medicine that calms the immune system is sometimes added when a cat does not respond to antibiotics alone, although most cats recover without it.

At home, it helps to keep your cat indoors, warm and quiet while it recovers, with food, water and the litter box close by. Check the gums and appetite each day, and call your vet if weakness or pale gums return.

Treatment often does not remove the bacteria completely, so many recovered cats stay carriers. They look healthy and have normal or near normal blood counts. The infection can flare up again later, for example during stress, another illness, or treatment that suppresses the immune system. Healthy carriers are usually not treated. In some situations, such as a cat with Mycoplasma haemofelis living with cats that have never had it, your vet may suggest a longer treatment plan to try to clear the infection.

Other pets and people

Hemoplasmas usually stay with one kind of animal. The species found in cats are different from those found in dogs, so passing the infection between cats and dogs is considered unlikely.

Other cats in the home can become infected, most likely through fights. Keeping tension and fighting between cats low is sensible. Ask your vet whether your other cats should be checked.

The risk to people is considered very low. An infection similar to Mycoplasma haemofelis has been described in a person with a weakened immune system who had many cat bites and scratches, but such cases are very rare. Washing your hands after handling a sick cat and cleaning any bite or scratch promptly is a good habit, especially for people with a weak immune system.

Prevention and newly adopted cats

There is no vaccine against these infections. Prevention focuses on the ways cats are exposed. Keeping cats indoors, or giving them safe and enclosed outdoor space, reduces fights with unknown cats. Regular flea and parasite control protects against other causes of anemia. It is also worth asking your vet about FeLV and FIV testing and FeLV vaccination, since these viruses can make hemoplasma disease worse.

Cats rescued from the street often have the main risk factors, such as life outdoors and fights with other cats. At Paw Squadron, the first stops after every rescue are the vet and a bath, with a checkup, deworming, and treatment against fleas and other parasites. Every animal gets a checkup, treatment, vaccinations and a microchip before adoption.

A cat can still carry hemoplasmas without any signs, and a routine checkup will not always find it. Moving to a new home is stressful, and stress can sometimes bring a hidden infection back. In the first weeks after adoption, check your cat's gums now and then and keep an eye on appetite and energy. It is a good idea to tell your vet about your cat's background, so they can consider this infection if anemia ever appears. If you are thinking about giving a rescued cat a home, our Adoptions page and FAQ explain how it works.