PCR vs. EM Adenovirus testing

Hello Everyone,

I have been hesitant to post on this subject. The controversy surrounding this embattled issue is upsetting but I do feel there are a few Adenovirus testing questions relating to the differences between PCR and EM testing that I can answer.

There have been some questions about the differences between blood vs fecal swabs as a specimen type for PCR testing. In theory blood can be used in place of a Cloacal swab only if the dragon has viremia (means the virus is found in the blood stream). If the virus is in the bloodstream it means basically that the host’s immune system has not been able to keep the virus in check. As a scientist you want to develop a method that has the best chance of picking up the virus so you look for the virus in the system that it affects first or lays dormant in. Adenovirus like particles have been found in the Liver which is part of the digestive system. Feces are excreted from the digestive system so this is the best place to find the virus. So the Fecal swab would be much more likely to find the virus if it is present in the animal. So if I was to develop a PCR Adenovirus test my sample type would be Feces.

Here are some of the differences between Polymerase Chain Reaction (PCR) and Electron Microscopy (EM). One of the big differences between PCR and EM is that EM is looking for whole adenovirus like particles and is also unable to distinguish between most types of adenovirus. In the PCR test you are looking for a specific sequence of DNA. Not to mention that DNA is inherently more stable than most viruses. When developing a PCR test of this nature your whole goal is to construct a primer that is specific for a species or strain that is habitually isolated from the particular animal of interest. So what I am saying is that you want to find a DNA sequence that is specific or only found in the animal of interest. In doing this you significantly narrow down the likelihood of picking up other types of Adenovirus. Another advantage of PCR is that in theory your PCR should be able to pick up DNA from animals that are not actively shedding whole virions (virus progeny). Here is the reason why, Infected cells like normal cells will eventually die and the cells will release DNA fragments into the feces even know the animal is not actively shedding large numbers of whole virus. The PCR method should be able to pick up some of this DNA from just the natural death of infected cells. This is another advantage of the PCR method.

Here is a great question asked on another forum:

When a beardie dies and is suspected to have AV, a necropsy is done and the liver is biopsied and looked at through an electron microscope, would it be safe to say that a DNA test at that point would also show the virus?

Yes, If you extract the DNA from the tissue and the animal has Adenovirus it will be picked up by PCR. In actuality one could also identify the Genus, species and hopefully someday the serotype or strain by PCR.

Kind Regards,

Randy