CT study points to earlier airway changes in cats with HARD: full analysis

A new feline heartworm imaging study suggests CT may give veterinarians a more objective way to detect early airway injury in cats with suspected heartworm-associated respiratory disease. In Veterinary Sciences, investigators reported that cats with respiratory signs and positive serology for Dirofilaria immitis had significantly higher CT-derived bronchial ratios than seronegative controls, supporting the idea that early feline heartworm disease leaves a measurable bronchial remodeling signature before more obvious vascular changes emerge. (mdpi.com)

The paper fits into a broader effort to better characterize HARD, the inflammatory pulmonary syndrome triggered when immature heartworms reach the lungs. That syndrome has been recognized for years, but diagnosis remains difficult because cats often have low worm burdens, transient or absent microfilaremia, and test results that can be hard to interpret. The American Heartworm Society’s updated feline guidelines say antibody testing can detect exposure earlier than antigen testing, but neither test is straightforward in cats, and antigen-negative results don’t exclude disease, especially in immature or male-only infections. (idexx.com)

In the new study, the researchers evaluated 38 cats: 30 seropositive cats with clinical signs compatible with HARD and eight asymptomatic seronegative controls. Their earlier Animals study in the same population found that all serum samples were antigen-negative despite the clinical and serologic suspicion, underscoring how elusive feline heartworm diagnosis can be. Across multiple lung lobes, the newer CT analysis found larger bronchial dimensions and higher normalized bronchial ratios in the suspected HARD group, while pulmonary artery changes were less consistent, pointing to bronchial remodeling as an earlier or more sensitive marker of disease in these cats. (mdpi.com)

That pattern also lines up with prior literature on feline lower airway disease and heartworm. A 2019 review in the Journal of Feline Medicine and Surgery noted that feline asthma and heartworm disease can share respiratory signs and imaging abnormalities, complicating case workups, and described HARD as part of a restrictive pulmonary process with airway wall thickening and other CT-visible changes. The FDA’s veterinary education materials similarly note that HARD can be hard to distinguish from feline asthma or bronchitis, which is exactly where more quantitative imaging markers could prove useful. (journals.sagepub.com)

There doesn’t appear to be substantial outside commentary on this specific paper yet, but the broader industry message is consistent. The American Heartworm Society said its updated feline guidance was driven in part by persistent underdiagnosis and undermanagement in cats. AAHA and AAFP guidance also emphasizes that prevention is preferable because diagnosis is challenging and treatment is difficult. Taken together, those positions support the study’s practical takeaway: better tools for presumptive diagnosis matter, even if CT won’t be available in every primary care setting. (heartwormsociety.org)

Why it matters: For veterinary teams, this study is less about replacing standard testing and more about sharpening clinical suspicion in the right cases. A coughing cat with a bronchial pattern, intermittent dyspnea, or asthma-like signs may still have HARD, particularly in endemic areas. Because the AHS recommends year-round prevention for all cats, including indoor cats, and notes that mosquitoes entering homes still create risk, the paper is another reminder that feline heartworm should stay on the differential even when pet parents perceive exposure risk as low. In referral practice, CT-derived bronchial indices may eventually help distinguish inflammatory airway remodeling related to immature heartworm infection from other lower airway disorders, or at least support a more confident presumptive diagnosis when serology and radiographs don’t tell a complete story. (idexx.com)

What to watch: The next step is external validation. Clinicians will want to know whether these ratios hold up in larger and more geographically diverse cat populations, how reproducible they are across scanners and readers, and whether they can separate HARD from asthma with enough confidence to change case management. Until then, the study mainly strengthens the evidence that early feline heartworm disease is often a bronchial disease first, and that prevention and thoughtful multimodal diagnosis remain the most useful tools in practice. (mdpi.com)