Reactivity of Horse Sera to Antigens Derived From Sarcocystis falcatula–Like and Sarcocystis neurona

Abstract

Sarcocystis neurona and Sarcocystis falcatula are protozoan parasites endemic to the Americas. The former is the major cause of equine protozoal myeloencephalitis, and the latter is associated with pulmonary sarcocystosis in birds. The opossum Didelphis virginiana is the definitive host of these parasites in North America. Four Didelphis species are found in Brazil, and in most reports in this country, Sarcocystis species shed by opossums have been classified as S. falcatula-like. It is unknown whether reports on S. neurona-seropositive horses in Brazil are also derived from exposure of horses to S. falcatula-like. The aim of this study was to test the sera reactivity of 409 horses in Brazil using antigens derived from a Brazilian strain of S. falcatula-like (Sarco-BA1) and from a North American strain of S. neurona (SN138). Samples were examined by immunofluorescent antibody tests (IFATs) at start dilutions of 1:20, and a selected number of samples was tested by Western blot (WB). Sera from 43/409 (10.5%) horses were reactive to S. falcatula-like and 70 of 409 (17.1%) were reactive to S. neurona antigen; sera from 25 animals (6.1%) were positive for both parasites by IFAT. A poor agreement was observed between the two employed IFATs (κ = 0.364), indicating that horses were exposed to more than one Sarcocystis species. Horse sera evaluated by WB consisted of four sera reactive to S. falcatula-like by IFAT, six sera positive to S. neurona by IFAT, two sera that tested negative to both parasites by IFAT, and a negative control horse serum from New Zealand. Proteins in the range of 16 and 30 kDa were recognized by part of IFAT-positive sera using both antigen preparations. We concluded that Brazilian horses are exposed to distinct Sarcocystis species that generate different serological responses in exposed animals. Antigens in the range of 16 and 30 kDa are probably homologous in the two parasites. Exposure of the tested horses to other Sarcocystis species, such as Sarcocystis lindsayi, Sarcocystis speeri, and Sarcocystis fayeri, or Sarcocystis bertrami cannot be excluded in the current study.

Reactivity against Sarcocystis neurona and Sarcocystis falcatula-like in horses from Southeastern and Midwestern Brazil

“…Although the clinical history of the horses in this study was not available, none of the animals presented neurological signs at the time of blood collection, therefore a less conservative cutoff was used. Exposure to different Sarcocystis species may also generate different immunological responses ( Borges-Silva et al, 2020 ). This could explain why horses in the present study reacted differently to S. neurona and S. falcatula -like antigens, with up to 8-fold increase in titers for S. falcatula- like and up to 16-fold increase in titers for S. neurona .…”

Sarcocystis neurona,Neosporaspp. andToxoplasma gondiiinfections in horses and equine protozoal myeloencephalitis (EPM): five decades of personal experience, perspectives and update

“…Another study revealed that proteins not related to S. neurona (C-reactive protein and amyloid A) were not elevated in the cases of EPM and had no diagnostic value (Mittelman et al ., 2018). Although S. neurona is morphologically related to T. gondii- like parasites, these parasites are antigenically and molecularly distinct from T. gondii (Dubey et al ., 2017b) and a species of Sarcocystis , S. falcatula (Borges-Silva et al ., 2020).…”

Sarcocystis neurona and related Sarcocystis spp. shed by opossums (Didelphis spp.) in South America

“…The poor agreement observed between the two IFATs (k = 0.364) indicated that the horses were exposed to more than one Sarcocystis species. Some IFAT-positive samples were also tested using IB (using the same isolates as antigens) and showed cross-reactivity to proteins in the range of 16 and 30 kDa (Borges-Silva et al, 2020).…”