Antigens of adults and third-stage larvae of the meningeal worm, Parelaphostrongylus tenuis (Nematoda, Metastrongyloidea)

Analysis of heavy-chain antibody responses and resistance to Parelaphostrongylus tenuis in experimentally infected alpacas

The parasitic nematode Parelaphostrongylus tenuis is an important cause of neurologic disease of camelids in central and eastern North America. The aim of this study was to determine whether alpacas develop resistance to disease caused by P. tenuis in response to a previous infection or a combination of controlled infection and immunization. Alpacas were immunized with a homogenate of third-stage larvae (L3) and simultaneously implanted subcutaneously with diffusion chambers containing 20 live L3. Sham-treated animals received adjuvant alone and empty chambers. The protocol was not effective in inducing resistance to oral challenge with 10 L3, and disease developed between 60 and 71 days following infection. Immediately following the onset of neurologic disease, affected animals were treated with a regimen of anthelmintic and anti-inflammatory drugs, and all recovered. One year later, a subset of alpacas from this experiment was challenged with 20 L3 and the results showed that prior infection induced resistance to disease. Primary and secondary infections induced production of conventional and heavy-chain IgGs that reacted with soluble antigens in L3 homogenates but did not consistently recognize a recombinant form of a parasite-derived aspartyl protease inhibitor. Thus, the latter antigen may not be a good candidate for serology-based diagnostic tests. Antibody responses to parasite antigens occurred in the absence of overt disease, demonstrating that P. tenuis infection can be subclinical in a host that has been considered to be highly susceptible to disease. The potential for immunoprophylaxis to be effective in preventing disease caused by P. tenuis was supported by evidence of resistance to reinfection.

Identification of antigens with potential for immunodiagnosis of Parelaphostrongylus tenuis and Elaphostrongylus cervi infections in red deer (Cervus elaphus elaphus)

Red deer (Cervus elaphus elaphus) were infected experimentally with Parelaphostrongylus tenuis in New Brunswick, Canada, and with Elaphostrongylus cervi in New Zealand. Excretory-secretory (E-S) antigens from adult P. tenuis were evaluated for their serodiagnostic potential in identifying P. tenuis and heterologous E. cervi infections in a Western blot. The antigen recognition profile of sera from animals infected with P. tenuis varied between individuals and with duration of infections, whereas that of pooled sera from animals infected with E. cervi showed less variation. A single molecule of 42-43 kDa was recognized consistently by sera from all animals infected with either P. tenuis or E. cervi. Sera from unexposed control deer and from those with other heterologous nematode infections did not consistently identify this antigen. Serorecognition of the 42-43-kDa antigen by deer infected with P. tenuis resulted in a sensitivity of 99% and a specificity of 85% (> or =1 mo postinfection). Although antibody to this antigen waned with time, the persistence of recognition up to 34 mo postinfection with P. tenuis exemplifies its diagnostic value. The sensitivity and specificity of diagnosis using this molecule were each 100% for identifying deer infected with E. cervi (> or =3 mo postinfection). Two other molecules from E-S of adult P. tenuis, 26-28 and 10-12 kDa, were also diagnostic, although their recognition was not persistent throughout infections. These 2 molecules may prove useful in combination with the 42-43-kDa antigen to help identify all infected animals during all phases of infections. This research represents the first conclusive identification of antigens with real potential for reliable antemortem immunodiagnosis of both P. tenuis infections and heterologous E. cervi infections.

Natural and experimental nematode infections in red deer (Cervus elaphus elaphus) and the potential for antemortem serodiagnosis of the tissue worm Elaphostrongylus cervi

Red deer (Cervus elaphus elaphus) were exposed to a variety of nematodes, either naturally on pasture (n = 12) or experimentally under controlled conditions (n = 30). Experimental exposures included a combination of one or more of Elaphostrongylus cervi, Dictyocaulus sp., and Muellerius capillaris. The prepatent period of E. cervi infections was 92–133 days post exposure (dpe) in 12 deer each given 20–42 infective larvae (L3) and maintained under controlled conditions. Adult E. cervi were recovered from all 12 animals at necropsy. The prepatent period of Dictyocaulus sp. was 23–37 dpe in 10 deer each given 100 L3 and maintained under controlled conditions. Adult Dictyocaulus sp. were recovered from seven animals at necropsy. No animal exposed to 42–54 M. capillaris L3 developed patent infections, nor were adult worms recovered at necropsy. There was no evidence of neurologic signs in any deer at any time during the experiment. An enzyme-linked immunosorbent assay (ELISA) using somatic protein extracts of adult E. cervi or those from the closely related nematode Parelaphostrongylus tenuis was evaluated. Although the ELISA was sensitive, it lacked specificity with heterologous infections. However, the close phylogenetic relationship of E. cervi to P. tenuis, and our ELISA results, suggest that molecules from P. tenuis may represent a viable alternative source for use in the future development of a reliable antemortem serodiagnostic assay for E. cervi.

Parasite proteomics

Proteomics offers a new set of tools for investigating parasites and parasite-associated disease. In this article, John Barrett, Jim Jefferies and Peter Brophy describe the key technologies involved, including two-dimensional gel electrophoresis, image analysis, biological mass spectroscopy and database searching. The potential applications of proteomics in drug and vaccine discovery are reviewed, as are possible future developments.

Evaluation of excretory-secretory products and somatic worm antigens for the serodiagnosis of experimental Parelaphostrongylus tenuis infection in white-tailed deer

Three different antigen preparations of Parelaphostrongylus tenuis were assessed for their effectiveness in an indirect enzyme-linked immunosorbent assay (ELISA) to diagnose experimental infection of white-tailed deer (WTD). The antigen preparations were the excretory-secretory products of third-stage larvae (ES-L3), somatic antigens of third-stage larvae (sL3), and somatic antigens of the adult stage (sA) of P. tenuis. The relative sensitivities of the antigen preparations in indirect ELISA were ES-L3 > sL3 > sA. Immunoglobulin G (IgG) antibodies to ES-L3 and sL3 could be detected 14 days postinfection and were consistently present in all infected animals from the first month to the end of the experiment at 5 months. In contrast, IgG antibodies to sA could not be detected at any time in 2 infected WTD. ES-L3 and sL3 proved reliable in the early detection of anti-P. tenuis antibodies and in the serological monitoring of experimentally infected animals. Significant cross-reactivity between all P. tenuis antigen preparations and sera from animals infected with parasites other than P. tenuis may preclude their use for field diagnosis. Nevertheless, isolation of unique P. tenuis antigen(s) should lead to the development of a specific serological test for infected white-tailed deer.