Evaluation of cobas Influenza A/B & RSV Test for Diagnosis of Equine Influenza

A comparative evaluation of seven commercial human influenza virus antigen detection kits for the diagnosis of equine influenza

BACKGROUND

Equine influenza virus (EIV) is one of the most important pathogens causing respiratory signs in equids. Rapid antigen detection (RAD) kits are useful for point-of-care testing because they are user-friendly and provide fast results. Although sensitive and broad-reactive RAD kits are needed for controlling horse movement, no RAD kits specified for EIV are available.

OBJECTIVE

This study evaluated the usefulness of seven RAD kits originally developed for human influenza and available in Japan during 2023-2024 for EIV antigen detection.

STUDY DESIGN

Experimental assay comparison.

METHODS

The detection limits of each RAD kit were determined using five-fold serial dilutions of two H3N8 EIV strains. According to the results of the detection limits, the three most sensitive RAD kits (Quick Chaser Auto Flu A, B, Finevision Influenza, and RapidTesta Flu·NEXT) were further evaluated using nasopharyngeal swabs of horses experimentally infected with EIV.

RESULTS

With reverse-transcription quantitative polymerase chain reaction (RT-qPCR) as a reference assay, the sensitivities of Quick Chaser Auto Flu A, B, RapidTesta Flu·NEXT, and Finevision Influenza were 63%, 61%, and 54%, respectively.

MAIN LIMITATION

Samples from naturally infected horses were not tested.

CONCLUSIONS

Since the sensitivities for detecting EIV antigens vary, choosing the appropriate RAD kits is essential. Although RAD kits are less sensitive than RT-qPCR, RAD kits are useful for detecting EIV antigens as ancillary diagnostic tools in the field.

Detection of equine influenza virus gene in the air around infected horses

Equine influenza virus (EIV) can be transmitted by inhalation of aerosolized droplets, direct contact, and contaminated fomites. However, to our knowledge, there are no reports of the recovery of EIV from the air surrounding infected horses. Here, we evaluated whether EIV can be recovered from the air in the stalls of experimentally infected horses by using an air sampler. Furthermore, we examined whether rapid molecular test kits with reaction times of less than 30 min can detect EIV from air samples for potential field application. Two horses kept in individual stalls were experimentally infected with EIV. Air samples were collected daily by using an air sampler until 13 days post-inoculation (dpi). Viral genes were detected in 26 out of 28 air samples from both horses at 1-13 dpi by real-time RT-PCR. A rapid molecular test kit based on real-time RT-PCR detected viral genes in 23 air samples from one horse at 1-9 and 12 dpi, and from the other at 1-13 dpi. These findings confirm that horses infected with EIV shed the virus into the air. Air sampling is safe for humans and horses and avoids the potential for injury when nasopharyngeal swabs need to be collected from untrained or aggressive horses. EIV RNA was detected in the air samples by using real-time RT-PCR or the rapid molecular test kit before the horses showed clinical signs. Thus, air samplers can detect EIV RNA as early as possible through routine testing in locations such as quarantine facilities.

Performance of a microfluidic immunofluorescence assay kit for equine influenza virus antigen detection

Equine influenza virus (EIV) infection is one of the most important respiratory diseases in the equine industry around the world. Rapid diagnosis, facilitated by point-of-care testing, is essential to implement movement restrictions and control disease outbreaks. This study evaluated a microfluidic immunofluorescence assay kit, which detects influenza virus and SARS-CoV-2 antigens in human specimens with a 12 min turnaround time, for its potential use in detecting EIV. The microfluidic immunofluorescence assay kit succeeded in detecting 11 EIV strains. Using the real-time reverse transcription polymerase chain reaction as a reference assay, the microfluidic immunofluorescence assay kit showed a sensitivity of 60.7% when evaluating nasopharyngeal swab samples of three horses experimentally infected with EIV. Comparing with the other two rapid antigen detection kits based on immunochromatography and silver amplification immunochromatography, the microfluidic immunofluorescence assay kit exhibited higher sensitivity than the former assay (53.6%) and the same sensitivity as the latter (60.7%). The microfluidic immunofluorescence assay kit did not detect nine non-EIV viruses including one equine coronavirus strain and seven bacteria, suggesting a high specificity for EIV antigens. Similar to other rapid antigen detection kits, the microfluidic immunofluorescence assay kit could be an effective diagnostic tool to detect EIV in the field.

Outbreak of equine coronavirus infection among riding horses in Tokyo, Japan

In 2020, an outbreak of equine coronavirus (ECoV) infection occurred among 41 horses at a riding stable in Tokyo, Japan. This stable had 16 Thoroughbreds and 25 horses of other breeds, including Andalusians, ponies and miniature horses. Fifteen horses (37 %) showed mild clinical signs such as fever, lethargy, anorexia and diarrhoea, and they recovered within 3 days of onset. A virus neutralization test showed that all 41 horses were infected with ECoV, signifying that 26 horses (63 %) were subclinical. The results suggest that subclinical horses played an important role as spreaders. A genome sequence analysis revealed that the lengths from genes p4.7 to p12.7 or NS2 in ECoV differed from those of ECoVs detected previously, suggesting that this outbreak was caused by a virus different from those that caused previous outbreaks among draughthorses in Japan. Among 30 horses that tested positive by real-time RT-PCR, ECoV shedding periods of non-Thoroughbreds were significantly longer than those of Thoroughbreds. The difference in shedding periods may indicate that some breeds excrete ECoV longer than other breeds and can contribute to the spread of ECoV.