Skip to main content
ARS Home » Midwest Area » Ames, Iowa » National Animal Disease Center » Virus and Prion Research » Research » Publications at this Location » Publication #246812

Title: Swine Influenza Update

item Lager, Kelly
item Baker, Amy
item CIACCI-ZANELLA, JANICE - Labex - Embrapa
item ZANELLA, ERALDO - Universidad De Passo Fundo
item Lorusso, Alessio
item Faaberg, Kay
item Kehrli Jr, Marcus

Submitted to: Swine Disease Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 10/16/2009
Publication Date: 11/5/2009
Citation: Lager, K.M., Vincent, A.L., Ciacci-Zanella, J.R., Zanella, E.L., Lorusso, A., Faaberg, K.S., Kehrli, Jr., M.E. 2009. Swine influenza update. In: Proceedings of the 17th Annual Swine Disease Conference, November 5-6, 2009, Iowa State University, Ames, Iowa. pp. 128-131.

Interpretive Summary:

Technical Abstract: On April 24, 2009, the Centers for Disease Control (CDC) confirmed an influenza epidemic was occurring in people and the genetic lineage was most closely related to influenza viruses known to be circulating in swine. The outbreak epicenter appeared to be in central Mexico and the virus spread to the United States and Canada by way of infected individuals early in the course of the pandemic. This proclamation that the virus was swine in origin led to a complex series of questions and politics that are still trying to be answered and addressed months later. This paper will summarize our efforts to answer some of the scientific questions with the political debate being left to others. In mid-April two children in Southern California with influenza like illness (ILI) had tested positive for a swine influenza-like virus [1]. This in and by itself was not unusual since several human swine flu cases have been detected annually over the last few years. What was unique about these two cases is that the children had no known contact with each other nor had visited any common sites or people, yet they were infected with almost identical viruses. Moreover, genetic analysis of the viruses revealed they were composed of a novel set of genes that had not been detected previously anywhere in the world. Within a few days it became clear this virus was transmitting from person to person in the United States and there was an epidemic of ILI in central Mexico that was spreading to the United States and Canada via the movement of infected people. A US Public Health Emergency was declared on April 26th and the CDC began to work closely with World Health Organization staff to try and control the spread of an apparently regional disease. Despite the best efforts of many, the H1N1 virus rapidly moved around the world leading to the declaration of a pandemic by June 11th, 2009. Since the genetics of the pandemic virus were novel, the obvious question was, would this virus have any unique phenotypic characteristics in swine? The following narrative summarizes research conducted at NADC since the start of the pandemic, followed by concluding statements. NADC in vivo studies. Beginning on May 1, 2009 we initiated a 4 pig study that followed our usual swine influenza virus challenge model, i.e., giving young pigs an intratracheal inoculation with 1 x 105 CCID50 of the pandemic virus isolate A/CA/04/2009 H1N1 (Vincent, unpublished data). The pigs were euthanized 5 days post inoculation (dpi), a time point that usually provides the peak virus load and extent of lesions when testing swine influenza virus (SIV) isolates. Using virus isolation and a real-time PCR assay, challenge virus was detected in nasal swabs and tissues associated with the respiratory tract in each of the 4 pigs. In contrast, virus was not isolated from sera or any other tissues collected from these pigs, although viral nucleic acid was detected in sera in two pigs and in a lymph node sample from 2 pigs. Pigs were moderately to severely affected following the inoculation having a rapid rise in body temperature and becoming dyspneic to a point of "thumping." Typically, there are few clinical signs following inoculation in our SIV challenge model; however, we have seen a similar response when pigs were given an H1N1 SIV challenge with A/swine/OH/07. The OH/07 virus was isolated from sick swine at an Ohio county fair during which a number of the swine show exhibitors developed ILI. An influenza virus was isolated from a child and parent that matched the swine isolate confirming the exhibitors had become infected with the swine virus. Based on a recent phylogenetic analysis [2], the OH/07 virus is from a cluster or clade of H1N1 SIV isolates that have emerged in the last few years known as the gamma clade. In a second animal study we inoculated pigs with