We have detected DNA from a protozoan parasite in lymph nodes of infected mice during 15 days after the infection. Could this DNA be related to live parasites?
Hi Alessandra,
It depends on the parasite's life cycle and physical characteristics as well as the temperature at which the samples are held. Parasites that have an environmentally persistent life stage, such as microsporidian spores, myxozospores, and some cysts or eggs can remain viable for some time inside a dead animal, particularly if the animal is refrigerated. I would not expect parasites that are present in the host only as trophozoites (or any parasites that cannot survive outside the host) to remain viable for such an extended period in a dead host, even if refrigerated. Many types of parasites do not survive freezing, although some can. However, DNA is quite stable if cold, and if the parasite DNA is protected, e.g., within a spore, egg, or cyst, it will remain detectable for an extended period even if the parasite is no longer viable.
Hi Marcus, I think I was not clear... My question is about the DNA viability of a dead parasite (protozoan) inside a live host. I want to know how long does DNA take to be degraded by the mammal immune system.
Fom our paper "Monitoring of the Parasite Load in the Digestive Tract
of Rhodnius prolixus...." : "The massive lysis event observed 24 hours after infection raised the possibility that the DNA
provided by the dead parasites could contribute to an overestimation of the parasite load in the gut. To assess the amount of DNA template released from dead parasites remaining in the digestive tract that could eventually be amplified by qPCR, we performed a controlled experiment using insects fed with blood containing 107 heat-killed parasites/ml (Fig 2C). In the AM and PM, 24 hours p.f. was sufficient to decrease the number of parasites to three logs below
that obtained with live parasites, whereas at four days p.f., the contribution of the remnant DNA fell to only 4 logs below that of insects fed with live parasites. Thus, the initial contribution of DNA from lysed parasites represents only ~ 0.1% of the total number of parasites. Finally, the kinetics of parasite DNA degradation by insect gut nucleases showed that 7 days were necessary to completely remove all of the remnant DNA
Thank you Pedro. Would you say that the kinetic of parasite DNA degradation by mammal immune system can be similar?
Probably not... this was luminal clearence by a digestive apparatus, but as the anterior midgut has very low (if any) proteolytic activity, the dissapearence was quite slow. My guess is that clearence from blood will be mediated by phagocytosis and receptors, and probably will be much faster. But this is just an educated guess
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