Characterization of the humoral immune response in alpacas (Lama pacos) experimentally infected with Fasciola hepatica against cysteine proteinases Fas1 and Fas2 and histopathological findings
Introduction
Fasciola hepatica infection is a serious problem to the alpaca farming by the loss in animal productivity and by the increased mortality observed in untreated animals (Leguía and Casas, 1999). The disease is highly prevalent along the high steppes of the Andes, where most of alpaca farms in Peru are found (Neyra et al., 2002). The transmission of the infection is facilitated by the heavy contamination of the pastures with the infective form, the climate that favors the parasite cycle and the lack of control programs against the fluke. Despite the importance of this infection by its negative impact in fiber productivity and quality, little is known of the liver pathology caused by F. hepatica in alpacas and the fluke factors associated to the pathogenesis of the disease. A differential susceptibility of the host to the fluke is a feature of the disease, being cattle able to mount a strong immune response that immunoprotects to subsequent infections and sheep develop little or absent immunoprotective response to F. hepatica infection (Mulcahy et al., 1999). It is not known whether alpacas become resistant to F. hepatica after a primary infection. However, herd screening suggests that alpacas are frequently re-infected in endemic areas (Neyra et al., 2002).
F. hepatica cysteine proteinases are abundantly expressed and secreted into the parasite gut lumen by the adult worm (Dalton et al., 2003). Fluke cysteine proteinases are reported as sensitive and specific markers for the serodiagnosis of fasciolosis in humans (Cordova et al., 1997, Cordova et al., 1999, O’Neill et al., 1998, Strauss et al., 1999), in sheep and cattle (Cornelissen et al., 1999, Cornelissen et al., 2001), and recently in goats (Ruiz et al., 2003). The major components of F. hepatica E/S products are cysteine proteinases, which are termed Fas1 and Fas2. Both parasite enzymes were purified by a simple procedure (Cordova et al., 1997) and evaluated as markers of the infection in alpacas that were naturally exposed to liver fluke in endemic areas (Neyra et al., 2002).
In the present study, we report an evaluation of the humoral immune response and liver histopathological findings in alpacas experimentally infected with F. hepatica.
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Experimental infection
Alpacas were obtained from SAIS Pachacutec, Junin, and transported to Lima, where they were kept for 2 months for adaptation to the housing conditions. Animals were selected on the field by checking for helminth infection and none of them were positive by coprology and serology to F. hepatica. As a preventive measure, all animals received a single dose of triclabendozole and closantel 1 month before the experimental infection. Animals were housed in an uncovered pen and fed with dry hay and
Experimental infection and blood cell count
All infected alpacas shed F. hepatica eggs 8 weeks PI. Eggs were detected in all faecal samples collected during the remaining 16 weeks of the experimental infection. Mature flukes were recovered from the livers of infected animals at necropsy and the parasite load averaged 41 ± 4 (Table 1). No weight loss was observed in the infected animals during the course of experimental infection (data not shown). Haematocrit count of infected animals was lower than controls 4 weeks PI and later (Fig. 1a).
Discussion
In this work, we established an experimental infection of alpacas with F. hepatica. The primary infection is similar to that observed in other species susceptible to F. hepatica infection: mature flukes shed eggs by the 8 weeks PI and adult worms were recovered from the bile ducts at necropsy (Chauvin et al., 1995, Clery et al., 1996, Ruiz et al., 2003). Hepatic lesions as wall thickening of bile ducts, disorganization of the liver parenchyma, stellate scar with fibrosis and destruction of bile
Acknowledgements
This work was partially funded by a grant B/2856-1 from the International Foundation for Science and INCAGRO CONTRACT 007-2003 to JRE. OT received Red SAREC support to conduct the experimental infection. OT and VN are graduate students supported by the Agreement between Consortium of Francophones Universities of Belgium (CIUF) and Universidad Peruana Cayetano Heredia (UPCH). Thanks to E. Chavarry for providing rabbit anti Fas2 IgGs. The authors wish to acknowledge the assistance and facilities
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