Type A Influenza Virus Detection from Horses by Real-Time RT-qPCR and Insulated Isothermal RT-PCR

Challenges in navigating molecular diagnostics for common equine respiratory viruses

Equine respiratory viruses remain a leading cause of equine morbidity and mortality, with the resurgence of certain infections, an increasing population of elderly, more susceptible horses, the growth of international equine commerce, and an expansion in geographic distribution of pathogens. The focus of rapid diagnosis of infectious diseases has also shifted recently, with the appearance and increasing importance of nucleic acid amplification-based techniques, primarily polymerase chain reaction (PCR), at the expense of traditional methods such as clinical microbiology. While PCR is fast, reliable, cost-effective, and more sensitive than conventional detection methods, careful interpretation of diagnostic test results is required, taking into account the clinical status of the patient, sample type, assay used and biological relevance of the detected viruses. The interpretation of common equine respiratory viruses such as influenza virus (EIV), alpha herpesviruses (EHV-1, EHV-4), arteritis virus (EAV) and rhinoviruses (ERAV, ERBV) is straight forward as causality can generally be established. However, the testing of less-characterized viruses, such as the gamma herpesviruses (EHV-2, EHV-5), may be confusing, considering their well-established host relationship and frequent detection in both diseased and healthy horses. For selected viruses, absolute quantitation (EHV-1 and EHV-4) and genotyping (EIV and EHV-1) has allowed additional information to be gained regarding viral state and virulence, respectively. This information is relevant when managing outbreaks so that adequate biosecurity measures can be instituted and medical interventions can be considered. The goal of this review is to help the equine practitioner navigate through the rapidly expanding field of molecular diagnostics for respiratory viruses and facilitate the interpretation of results.

Clinical observations and molecular detection of Type-A influenza virus in some of the family Equidae in eastern Saudi Arabia winter-2019

OBJECTIVES

In the current study, we are investigating the viral causes of some respiratory clinical signs in some animals belongs to the family Equidae in eastern Saudi Arabia (ESA) during winter- 2019. We observed the progression of severe respiratory clinical signs among some horses, donkeys, and ponies in the ESA. Animals showed rapid respiration, fever, nasal discharges (started as serous then changed into mucopurulent with the progression of the infection per some animals). We conducted a longitudinal study to monitor the progression of this outbreak. We conducted molecular surveillance for the influenza virus Type-A using real-time PCR and regular RT-PCR. We also conducted a serosurveillance of the virus in sera of the tested animals using the commercially available enzyme-linked immunosorbent assay (ELISA).

RESULTS

The molecular detection of the Influenza virus type-A virus from nasal swabs of the affected animals using the real-time PCR results clearly showing that 35.1% of the tested horses, donkeys, and ponies were positives. Further confirmation was achieved by reporting the seroconversion of some of the affected animals. Several attempts were conducted to isolate the circulating influenza strains using the embryonated chicken eggs were unsuccessful. This was based on the absence of any amplicons in the harvested embryonated egg fluids using some oligonucleotides for the common influenza virus genes (HA, NA, M, and N). Meanwhile, ELISA results revealed the detection of the antibodies in sera of horses and donkeys 72.9%. Seroconversion was reported in many animals several weeks after the onset of the outbreak. Taken together all these pieces of evidence, we confirm an influenza virus type-A outbreak among the tested animals during winter 2019.