>> have some problems understanding the seasonal factor<<
Here are a few comments on co-infections with coronaviruses, which may be a significant issue in the Fall or Winter:
cmbi.bjmu.edu.cn
"Co- or Sequential Infections
The other factor that is important in terms of SARS is this question of whether there are concurrent or sequential respiratory viral infections, and whether these exacerbate the SARS coronavirus infections. What I want to show here is a precedent for that in animals, a recent study conducted by a master's DVM student in my lab, Dr. Hayes. In this study, he infected pigs with a porcine arterivirus which in the Nidovirales order, which is the same order as the coronaviruses are in. He gave them this PRRS virus first, and then PRCV after five days. What he found in this study was a longer shedding of PRCV after the dual infections, and the fecal shedding of PRCV was more common after the dual infections. We don't understand the reason for that at this time, but we can speculate on several hypotheses. He also found—also the group in Belgium, Van Reuth and Pensaert, found—that there was prolonged fever, respiratory disease, and reduced weight gain after these dual infections.
This shows a normal pig lung tissue; this is what the tissue looks like after PRCV infection, and this is after the dual infection. I want to point out there is a lot of infiltration here of monocytes in the lung. They are some of the major lesions that are seen, as well as some inflammation in the lungs.
The other study I think is quite pertinent with what we're seeing happening the world today is the study from Van Reuth and Pensaert in Belgium that showed if they gave PRCV first and then they infected pigs with swine influenza two days later, they had severely enhanced respiratory disease compared to either virus alone. Often it's hard to reproduce some of these respiratory viral infections in an animal model, so this has relevance because recently avian influenza outbreaks have been diagnosed in the Netherlands, so I think we can imagine what might happen if both of these viruses co-infected people together.
Other factors have been defined from animal studies. These, again, were mixed infections, dual infections with PRCV, or with PRRS, or with PRCV followed by bacterial LPS in five days. These animals were found to develop more severe respiratory disease after LPS exposure and enhanced fever, compared to pigs inoculated with each agent alone. Again, this may have relevance to SARS cases if there are secondary bacterial infections. " |
