Abstract
Influenza viruses are among the most important respiratory pathogens in pigs and humans. They cause seasonal epidemics in pigs and occasional pandemics in humans. Herbal remedies have been regarded as suitable elements to aid in controlling influenza. This study was carried out to analyse the effects of the in-feed administration of glycyrrhizic acid, the best-known component of liquorice (as Viusid-Vet® powder), in pigs suffering an outbreak of influenza. Eighty crossbred Duroc-Landrace pigs, one day post-weaning (22 days old), were included in this trial. Piglets were randomly divided into the following two groups: those treated with glycyrrhizic acid and an untreated control group. Serological measurements to assess viral load and humoral responses were carried out. Blood samples from pigs were obtained every fortnight, starting on week two and ending on week 15. With these samples, haemagglutination inhibition (HI) tests were performed, using A/swine/New Jersey/11/76 (H1N1) and A/swine/Minnesota/9088-2/98 (H3N2) as reference viruses. Quantitative RT-PCR tests against the M gene of the influenza virus were also performed to assess viral shedding from nasal swab samples on weeks 1 to 8 after the beginning of the trial. Weight variables were assessed weekly for 18 weeks. In the HI tests, treated animals showed fewer positive responses compared to the control group for H1N1 and H3N2. However, a positive response to viral protection, as assessed by HI tests, was regarded as not conclusive of humoral immune stimulation. qRT-PCR tests for viral spread exhibited a lower rate of excretion for the treated group compared to the untreated one. Hence, it appears that glycyrrhizic acid stimulates, to some extent, immune responses against pig influenza as measured by viral shedding. For mean body weight, the generalized estimating equations show a higher weight gain for pigs treated with glycyrrhizic acid than the control group (P = 0.0001). These effects may assist producers in addressing the aftermath of an influenza outbreak.Figure 1. Results of RT-PCR viral shedding test against the M gene. (Likelihood χ21,7 = 19.2 P = 0.0001).
Highlights
Intensive pig farming entails a great danger regarding the presentation and prevalence of diseases, respiratory ones
In the haemagglutination inhibition (HI) tests, treated animals showed fewer positive responses compared to the control group for H1N1 and H3N2
In the HI test used to detect antibodies against H1N1 tests on week two, the glycyrrhizic acid-treated group showed fewer positive responses compared to the control group (47.3 % vs 61.1 %)
Summary
Intensive pig farming entails a great danger regarding the presentation and prevalence of diseases, respiratory ones. Producers often need to vaccinate their animals after maternal antibodies decrease, that is, when they are 10-13 weeks old.[4] A vaccine can completely protect against influenza if antibody titres against the challenge virus are sufficiently high, a relatively rare event.[5] Apart from the vaccine strain, the adjuvants and antigenic dose may play a crucial role in vaccine efficacy. Immune-modulating substances may help the animals achieve the high antibody titre required for full protection.[1,3] it has been postulated that drugs or products that can optimize immune responses may be beneficial to the health status of the farm and improve production variables while maintaining a favourable cost:benefit ratio.[6,7] In pigs, such a drug preparation should ideally be administered orally, be virtually innocuous to animals, and not pose a public health threat, i.e., drug residues in animal tissues should not be a concern
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