Mycoplasma infections in cats are caused by tiny bacteria that lack a cell wall, making them unlike most other bacterial infections. These organisms fall into two main categories: hemotropic mycoplasmas (called hemoplasmas) that attach to red blood cells and cause anemia, and respiratory mycoplasmas that colonize the airways, eyes, and lungs. The specific cause depends on which type of mycoplasma is involved, but the most common route of infection is direct contact with an infected cat, typically through bites and scratches during fights.
The Mycoplasma Species That Infect Cats
Three hemotropic species cause blood infections in cats. Mycoplasma haemofelis is the most dangerous, capable of triggering severe or even fatal anemia in otherwise healthy cats. It was previously known as Haemobartonella felis before being reclassified. Two other species, Candidatus Mycoplasma haemominutum and Candidatus Mycoplasma turicensis, also infect cats but generally cause milder disease unless the cat’s immune system is already compromised.
A separate group of mycoplasma species targets the respiratory tract. These are found in cats with conjunctivitis, upper respiratory infections, chronic bronchitis, and feline asthma. Because mycoplasmas have very small genomes, they can’t produce all the nutrients they need on their own. They survive by colonizing mucosal surfaces and drawing resources from host cells, producing hydrogen peroxide that directly damages the tissue they attach to.
How Cats Get Infected
For the blood-borne hemoplasmas, the strongest evidence points to direct transmission through biting and scratching during cat fights. When an infected cat bites another cat, the bacteria in its blood can enter the wound. This explains why the same risk factors that predict feline immunodeficiency virus (FIV) infection, which also spreads through bite wounds, predict hemoplasma infection as well.
Fleas have long been suspected as a transmission route, but the evidence is weaker than many cat owners assume. In experimental studies, cat fleas transmitted Mycoplasma haemofelis to only one out of six cats after heavy infestation with 100 fleas from an infected cat. The other main hemoplasma species wasn’t transmitted by fleas at all in the same experiment, and neither species spread when cats ingested infected fleas. Researchers have concluded that fleas are, at best, an occasional mechanical carrier rather than a primary vector. Ticks and mosquitoes have shown even less potential for spreading the infection.
Respiratory mycoplasma spreads through close contact between cats, particularly in shelters, boarding facilities, and multi-cat households. Shared air space, grooming, and contaminated hands or surfaces all play a role. Wearing gloves and washing hands between handling cats in these environments helps reduce transmission.
Risk Factors That Make Infection More Likely
Certain cats are far more likely to test positive for hemoplasma infection. In a large study using multivariate analysis, three factors stood out as statistically significant:
- FIV-positive status increased the odds of hemoplasma infection by roughly 10 times. This likely reflects both a shared transmission route (bite wounds) and the immune suppression that FIV causes, which may allow hemoplasmas to establish infection more easily.
- Male cats were about 5 times more likely to be infected, consistent with the fact that intact males fight more frequently.
- Non-pedigree (mixed breed) cats had about 3 times the odds of infection, probably because they’re more likely to roam and encounter other cats.
Outdoor access and a recent history of cat bite abscesses are also loosely associated with infection. Cats older than 10 years were about 3 times more likely to carry one of the milder hemoplasma species, possibly due to accumulated lifetime exposure. Interestingly, FeLV infection, season of the year, and anemia status were not significant risk factors in the same analysis.
Symptoms of Blood vs. Respiratory Infection
Hemotropic mycoplasma attacks red blood cells directly. The bacteria attach to the surface of the cells, and the cat’s own immune system then destroys the affected cells, creating what’s called immune-mediated hemolytic anemia. Cats with Mycoplasma haemofelis may develop pale gums, lethargy, loss of appetite, rapid breathing, and sometimes a fever. In severe cases, the red blood cells clump together (agglutination), and a blood test called a Coombs’ test will come back positive. This form can be fatal without treatment.
Respiratory mycoplasma looks quite different. Cats typically develop coughing, rapid breathing, or labored breathing. In one study of cats with feline asthma and chronic bronchitis, coughing was the most common sign, present in the vast majority of affected cats. Conjunctivitis (red, watery, or goopy eyes) and nasal discharge are common with upper respiratory involvement.
How Mycoplasma Is Diagnosed
For blood infections, veterinarians historically looked at blood smears under a microscope to spot the bacteria clinging to red blood cells. This method is unreliable. False positives happen when staining artifacts mimic the bacteria, and false negatives happen because the number of bacteria in the blood fluctuates over the course of infection. A cat can be actively infected and still have a clean-looking smear.
PCR testing, which detects the bacteria’s DNA, is now the preferred method. It’s far more accurate and can distinguish between the different hemoplasma species, which matters because treatment urgency and prognosis vary. One point-of-care PCR assay showed 78% sensitivity and 96% specificity, meaning it catches most true infections while rarely producing false alarms. Your vet may combine PCR with a complete blood count to assess the severity of anemia.
Treatment and Recovery
Doxycycline is the first-line antibiotic for both blood and respiratory mycoplasma infections. For respiratory infections, a typical course runs 7 to 10 days. If the cat responds well but has chronic disease, treatment continues for at least one week past the point where symptoms resolve. For cats that don’t tolerate doxycycline, minocycline and certain fluoroquinolones are alternatives that also work against mycoplasma.
For hemotropic infections, the antibiotic course is often longer, and cats with severe anemia may need supportive care including blood transfusions. Even after treatment, some cats remain chronic carriers of the bacteria without showing symptoms. This is particularly true for the milder hemoplasma species. A carrier cat can potentially transmit the infection to other cats through future bite wounds, which is one reason indoor-only living and reducing inter-cat aggression matter for prevention.
Can Humans Catch It From Cats?
Mycoplasma species have been detected in a range of mammals, including humans, and occasional reports of cross-species transmission suggest some zoonotic potential. However, feline hemoplasmas are not considered a well-established human health threat. The risk appears to be very low for healthy people, though immunocompromised individuals may want to take standard hygiene precautions when handling cats known to be infected.