Longitudinal detection of Sarcocystis aucheniae DNA in blood samples of naturally infected alpacas in the Andean highlands of Peru

Sarcocystis aucheniae is a protozoan parasite that forms macroscopic cysts in the skeletal muscles of South American camelids (SAC), impairing meat commercialization and posing a significant barrier to sustainable camelid livestock development. Although S. aucheniae DNA has been previously detected in SAC blood, the temporal dynamics of parasitemia remain unclear. This study presents the first longitudinal analysis of S. aucheniae DNA detection in alpaca (Vicugna pacos) peripheral blood. Monthly blood samples were collected from 38 male alpacas over 10 months in a SAC breeding establishment in Yanque, Peru. A duplex semi-nested PCR was used to detect DNA from parasites and the host, the latter as an extraction control. Sarcocystis aucheniae was detected in 9 animals (24 %) during the study. The maximum time length of positive detection was 2 months in 2 alpacas, while the rest of the animals tested positive in only one sampling. This suggests a brief window of blood-circulating stages, before encysting in the muscles. In one alpaca, positive and negative detection alternated in consecutive months, which might indicate fluctuating parasitemia levels, or re-infection. No correlation was found between PCR positivity and host age, temperature, or precipitation. Primer specificity was assessed by in silico alignments, and analytical sensitivity was estimated at 0.46 pg/μl of DNA. Although the method has limited diagnostic value in chronic infections, it is useful for epidemiological surveillance and transmission monitoring. This study provides novel insights into the infection kinetics of S. aucheniae and highlights the value of molecular tools in understanding parasitic transmission in SAC.