Abstract
On 18 June 2020, Alvarez et al. published their article titled “Seroprevalence of influenza D virus in bulls in Argentina.” 1 It is an interesting work in which the authors evaluated the influenza D virus (IDV) seroprevalence rates in bulls in the province of La Pampa, Argentina. Despite its strengths and scientific value, some technical issues should be further considered and discussed.
First, the collection and storage conditions of the 165 banked serum samples, which had been stored in the serum bank of INTA (Instituto Nacional de Investigación Agropecuaria), were not noted in the manuscript. It is important to maintain the stability of samples through cold-chain transport from collection to storage. The storage temperature of the banked serum samples may influence the anti-IDV antibody titer. A study explored the impact of storage temperature and the use of LSF (labile serum factor) against selective arboviruses in infected humans; the neutralization-enhancing effect of LSF was absent in serum stored at 24°C for 15 d. 2
Second, the key to the seroprevalence study was the anti-IDV antibodies, which were tested by an in-house indirect ELISA. 3 According to the article, “We used 165 serum samples, which had been collected in 2013 to estimate the seroprevalence of reproductive diseases in bulls, such as bovine brucellosis, and had been stored in the serum bank of the Instituto Nacional de Investigación Agropecuaria (INTA) in Anguil, La Pampa”; the serum specimens had been collected in 2013 for other studies and stored for 6 y. The stability of the anti-IDV antibodies during long-term storage may have influenced the results of the seroprevalence survey; antibody titers may have decreased, especially of the seropositive samples near the cutoff titer.
The relationship between storage temperature, time, and anti-IDV antibody should be further analyzed. The storage time and temperature of long-term stored blood specimens should be included in the “Materials and Methods” during seroprevalence studies of IDV in the future. If the seropositive serum samples for IDV in this study were still stored in the serum bank of INTA, we strongly advise that the in-house indirect ELISA should be performed under different storage time and temperature conditions.