Note: Today is my last full day in St. Augustine, I’ll be back on the road home tomorrow. I expect to resume my full blogging schedule on Monday.
# 4953
Different viruses have an affinity for different types of cells. That is why most viruses are selective as to what organ systems they attack, or even what species are susceptible.
This explains why a virus might affect a dog, or a cat, or a bird, yet not affect humans. This species selectivity is known as a `host range'.
Most viruses generally have a fairly narrow host range (there are exceptions, of course. Like rabies).
One of the surprises coming out of the emergence of the 2009 H1N1 pandemic virus was its ability to infect wide range of species.
This wasn’t completely unprecedented with flu viruses, since we’ve seen this kind of pattern with the H5N1 bird flu – but it is unusual for a `humanized’ influenza virus.
Cats, which normally are not susceptible to human influenza viruses, were reportedly stricken in a number of households (see H1N1 Infected Cat Dies In Oregon).
Which serves as prelude to a study that appears ahead-of-print in the CDC’s EID Journal titled:
Experimental Pandemic (H1N1) 2009 Virus Infection of Cats
DOI: 10.3201/eid1611.100845
van den Brand JMA, Stittelaar KJ, van Amerongen G, van de Bildt M, Leijten LL, Kuiken T, et al. Experimental pandemic (H1N1) 2009 virus infection of cats. Emerg Infect Dis. 2010 Nov; [Epub ahead of print]Conclusions
Intratracheal infection of domestic cats with pandemic (H1N1) 2009 virus resulted in mild-to-moderate clinical signs and virus replication throughout the respiratory tract that caused diffuse alveolar damage.
Pathogenic changes in the respiratory tract in cats were similar to those that occur in humans, macaques, and ferrets (7,11–13). Seroconversion of sentinel cats indicated cat-to-cat transmission.
The full study runs about 4 pages, with heavy emphasis on the necropsy and histological examination of these laboratory cats several days post infection.
Those discomforted by such details might want to skip the full paper.
While producing less dramatic symptoms, cats infected with the pandemic H1N1 virus showed similar pathogenic processes to cats infected with the HPAI H5N1 bird flu virus.
Again, from the study:
Histopathologic and immunohistochemical findings in lungs of cats infected with these viruses coincided, which indicated a similar pathogenetic process and increased severity in cats infected with HPAI virus (H5N1).
However, in contrast to HPAI virus (H5N1), pandemic(H1N1) 2009 virus does not cause extrapulmonary lesions in infected cats.
Promiscuous viruses - those capable of expanding their host range - are a bit more worrisome because they have more opportunities to mutate, reassort, or evolve.
And the more diverse their host range, the better the chance that the virus can find a way to survive long term.
We’ve seen reports of swine, ferrets, turkeys, cats, and dogs infected with H1N1 virus over the past year, and similar reports for the H5N1 avian flu over the past decade as well.
A few essays on these include:
Mixing Vessels For Influenza
US: Dog Tests Positive For H1N1
US: Turkey Farm Reports H1N1
Cat Got Your Virus?
While none of this necessarily represents a clear and present danger to humans, it does illustrate how much more we have to learn about how influenza viruses work.
