Larval cyathostominosis results from the mass emergence of encysted larval stages from the large intestinal wall. There is currently no routinely available noninvasive method to enumerate cyathostomin encysted larvae, and horses with high burdens may have low or negative FECs (Dowdall et al. 2002). Furthermore, horses with larval cyathostominosis often have no specific discriminating clinical signs. A noninvasive diagnostic test for encysted larvae would assist in the diagnosis of larval cyathostominosis and would aid in the identification of horses requiring larvicidal treatments. Previously, Dowdall et al. (2002, 2004) demonstrated that serum IgG(T) responses to 2 larval native antigen complexes (of 20 and 25 kDa in size) were observed to be significantly higher in clinical cases than in cyathostomin-naïve or -negative animals. Moreover, in experimentally-infected animals, anti-25 kDa complex IgG(T) levels correlated positively with field exposure and, importantly, with burdens of EL3 (r(s) = 0.74, P = 0.015) and total mucosal parasites (r(s) = 0.78, P = 0.010). In naturally infected horses, whose parasite burdens were quantified post mortem, antigen-specific IgG(T) responses were also significantly higher in infected than in uninfected horses (P = 0.0001 and 0.002 for anti-25 and anti-20 kDa responses, respectively). In these horses, anti-25 kDa IgG(T) levels correlated positively with mucosal and luminal burdens (P<0.05). In terms of IgG(T) responses to the 20 kDa antigen complex, levels correlated positively with luminal burdens only (P = 0.0043) (Dowdall et al. 2004). Antigens within the complexes were shown to be specific to the cyathostomin group, with no or limited cross reactivity to other helminth species (Dowdall et al. 2003). As these antigens are time-consuming to prepare and rely on a continuous source of tissue from infected animals, representative recombinant proteins have been produced in Escherichia coli (McWilliam et al. 2010). Recently, genes encoding 2 antigenic proteins, cyathostomin gut associated larval antigen (Cy-GALA) and cyathostomin immuno-diagnostic antigen (Cy-CID), that are produced by encysted larval stages, were isolated and the proteins expressed in E. coli. A number of recombinant Cy-GALA proteins, representative of common cyathostomin species, have now been produced. These proteins exhibit no reactivity to serum from horses specifically infected with other noncyathostomin species, nor does antiserum, raised to one of the proteins, bind to worm extracts from other species. Initial data suggest that recombinant GALA proteins have diagnostic potential and a patent application is under review. Further development of this assay is directed at increasing cyathostomin species coverage for the proteins Cy-GALA and Cy-CID, to ensure that the assay is sensitive to the presence of other, less common cyathostomin species. It is anticipated that a diagnostic assay based on detection of antibodies to a cocktail of these recombinant proteins will be developed for commercial use in the next 3–5 years.
Mast cell counts and their proteinase (chymase/tryptase) expression may also offer predictive value for the determination of total (including mural) cyathostomin burdens. The intestinal immune response to cyathostomin infection is not fully understood, although increased mast cell numbers have been documented in the large intestine of horses naturally infected with cyathostomins, with a linear correlation observed between magnitude of caecal cyathostomin burden and both toluidine blue stained, and chymase- and tryptase-labelled mast cell populations (Pickles et al. 2010). Development of a noninvasive serological or rectal biopsy assay for mast cells or their proteinases is ongoing and could represent a advance in the in vivo diagnosis of active cyathostomin infection in future.