CT study points to earlier airway changes in cats with HARD
Bottom line
A new CT-based study adds objective imaging evidence that cats with clinical signs and serologic findings compatible with heartworm-associated respiratory disease, or HARD, show measurable early bronchial remodeling. In a cohort of 38 cats, researchers compared 30 symptomatic, Dirofilaria immitis-seropositive cats with eight asymptomatic seronegative controls and found significantly higher bronchus-to-artery and bronchus-to-vertebral body ratios across multiple lung lobes in the suspected HARD group, while pulmonary vascular changes were less pronounced. The work, published in Veterinary Sciences, builds on the group’s earlier Animals paper and suggests CT morphometric indices may help quantify airway injury in feline heartworm cases that can be difficult to confirm with routine testing alone. (mdpi.com)
Why it matters: For veterinary professionals, the study reinforces a familiar challenge: feline heartworm disease often presents as respiratory disease first, and standard diagnostics can miss it. The American Heartworm Society says antigen testing alone can’t reliably rule out heartworm disease in cats because immature infections and male-only infections are common, and it recommends routine heat treatment of samples for antigen recovery plus annual testing. The same guidelines also stress year-round prevention for all cats, including indoor cats, because mosquitoes enter homes and a meaningful share of infected cats are reported as indoor-only. In practice, that makes these CT-derived airway measurements less of a screening tool and more of a useful adjunct in referral or specialty settings when a coughing or dyspneic cat has equivocal serology and imaging findings that overlap with asthma or bronchitis. (idexx.com)
What to watch: The next question is whether these CT indices can be validated in larger cohorts, tied to outcomes, and translated into clearer diagnostic pathways for differentiating HARD from feline asthma in everyday practice. (mdpi.com)
Key facts
- Study type
- CT-based imaging study
- Journal
- Veterinary Sciences
- Condition
- Heartworm-associated respiratory disease (HARD)
- Sample size
- 38 cats
- Groups compared
- 30 symptomatic, Dirofilaria immitis-seropositive cats and 8 asymptomatic seronegative controls
- Main finding
- Suspected HARD cats had significantly higher bronchus-to-artery and bronchus-to-vertebral body ratios across multiple lung lobes
- Other finding
- Pulmonary vascular changes were less pronounced
- Earlier study result
- All serum samples were antigen-negative despite clinical and serologic suspicion
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)