Abstract
Background:
Feline upper respiratory tract disease (URTD) is associated with acute inflammatory responses. Serum amyloid A (SAA) is a sensitive biomarker of systemic inflammation in cats. However, despite clear clinical resolution, SAA concentrations may remain elevated, and the optimal management of such cases remains unclear. Huaier, a polysaccharide-rich fungal extract containing the bioactive component TPG-1, has been reported to exhibit immunomodulatory effects in both experimental and clinical studies; however, its potential relevance in feline infectious or inflammatory diseases has not been established.

Case Description:
This case series describes two cats with confirmed URTD in which serum SAA concentrations remained persistently elevated despite complete clinical resolution and extensive diagnostic evaluation that failed to identify ongoing systemic inflammatory or neoplastic diseases. Polymerase chain reaction testing detected feline upper respiratory pathogens, including feline herpesvirus type 1, feline calicivirus, and Mycoplasma species. Huaier, an orally administered polysaccharide-rich fungal extract containing TPG-1, was introduced at the owner’s request. SAA concentrations gradually normalized in both cats following Huaier administration and remained within the reference interval during the long-term follow-up. No recurrence of clinical signs was observed after normalization of SAA concentrations.

Conclusion:
These cases describe the normalization of persistently elevated serum SAA concentrations and sustained clinical stability following Huaier administration in cats with URTD. Although a causal relationship cannot be established based on these two cases, the temporal association suggests that Huaier warrants further investigation as a potential adjunctive option for managing persistent subclinical inflammatory activity following feline URTD. These observations should be interpreted as hypothesis generation rather than evidence of therapeutic efficacy.

Key words: Cat; Huaier; Serum amyloid A; Subclinical inflammatory; Upper respiratory tract disease.