Ferrets and mice are often used in influenza research, but neither is truly ideal.
So in recent years a number of researchers have looked at guinea pigs as possible model mammalian host for influenza virus studies (see PNAS The guinea pig as a transmission model for human influenza viruses by Peter Palese et al. 2006).
The success in using guinea pigs in lab studies has led some scientists to wonder just how guinea pigs might fit into the hosting and spread of flu viruses outside of the laboratory.
Which brings us to a dispatch (again from Peter Palese et al.) that was published yesterday in the EID journal called:
Victor H. Leyva-Grado, Samira Mubareka, Florian Krammer, Washington B. Cárdenas, and Peter Palese
To determine whether guinea pigs are infected with influenza virus in nature, we conducted a serologic study in domestic guinea pigs in Ecuador. Detection of antibodies against influenza A and B raises the question about the role of guinea pigs in the ecology and epidemiology of influenza virus in the region.
Guinea pigs are raised and used as food in parts of South America (Peruvians reportedly consume more than 65 million of them each year, and they may also be found on the menu in Bolivia, Ecuador, and Columbia).
While the consumption of guinea pigs may seem an unusual culinary choice to many of us, it is so entrenched in the Andean culture that in 1753 - when Marcos Zapata painted his version of `The Last Supper’ for Peru (which now hangs in The Cathedral Of Cusco ) - he depicted Christ and the Apostles dining on a platter of cuy, or guinea pig.
Photo Source – Wikipedia.
But I digress . . .
Most of these animals are raised on small farms, and often in close contact with other livestock as well as humans.
Given these conditions, and their propensity for hosting and spreading influenza in laboratory studies, a seroprevalence study was undertaken to see how widespread influenza infection among guinea pigs might be outside of the laboratory.
This study examined blood samples from 40 guinea pigs taken from 3 locations across Ecuador, and subsequently found evidence of previous Influenza A infections in a unusually large number of them.
The surprises (of which there were several) included:
- The high percentage of positive influenza A samples (50% H1, 45% H3)
- The detection of several (n=14)animals carrying antibodies to an H5 virus
- And perhaps the biggest surprise of all – finding evidence of influenza B infections (previously only thought to infect humans) in 27 of the 40 samples tested.
An earlier seroprevalence study of influenza A among humans in Ecuador showed a seroprevalence of H1 (5.1%) and H3 (5.5%) - about 1/10th that found in these guinea pigs.
The authors suggest that the way these animals are raised (caged together and in close quarters) may facilitate the spread of influenza.
The discovery of H5 antibodies is intriguing, but since this study only tested only for seroreactivity to parts of the H5 virus, further study will be required to identify and quantify the prevalence of avian influenza viruses in this population.
And the last finding - that of Influenza B in roughly 2/3rds of the samples – support the idea that this type of influenza can be readily transmitted from humans to other hosts.
The authors write:
Further studies are needed to isolate and characterize the type B influenza virus present in the population of guinea pigs to determine if there has been an adaptation to the new host or if the guinea pig is only a transient reservoir for the human virus.
The authors conclude this dispatch by stating:
We did not determine whether guinea pigs are an incidental host for influenza virus infection or, if instead, the virus has been adapted to these animals or if guinea pigs are a natural reservoir for some influenza viruses. To this end, virus isolation and characterization would be necessary to determine the virus strains circulating in this population. In the laboratory, guinea pigs are infected and efficiently transmit influenza viruses to naive hosts without showing any overt clinical signs of disease (1). Therefore, further studies are needed to address the specific role of guinea pigs raised as livestock in the ecology and epidemiology of influenza viruses in the region.
For more details on the methods used, the full text is available online at this link.
While this research might seem a bit obscure to all but the most ardent infectious disease geeks, it serves to show just how little we still know about influenza viruses and their host range, and that there are still plenty of surprises waiting out there yet to be uncovered.