Animal Health

Three classes of IgG have been described for camelids. IgG1 has a conventional four-chain structure, while IgG2 and IgG3 do not incorporate light chains. The structures and antigen-binding affinities of the so-called heavy-chain classes have been studied in detail; however, their regulation and effector functions are largely undefined. The aim of this study was to examine the participation of conventional and heavy-chain IgG antibodies in the camelid immune defense directed against West Nile virus (WNV). We found that natural infection or vaccination with killed WNV induced IgG1 and IgG3. Vaccination also induced IgG1 and IgG3; IgG2 was produced during the anamnestic response to vaccination. When purified IgGs were tested in plaque-reduction neutralization titer (PRNT) tests, IgG3 demonstrated PRNT activities comparable to those of conventional IgG1. In contrast, IgG2 demonstrated only suboptimal activity at the highest concentrations tested. Flow cytometric analysis revealed that macrophages bound IgG1, IgG2, and IgG3. Furthermore, subneutralizing concentrations of all three isotypes enhanced WNV infection of cultured macrophages. Our results document distinctions in regulation and function between camelid heavy-chain isotypes. The reduced size and distinct structure of IgG3 did not negatively impact its capacity to neutralize virus. In contrast, IgG2 appeared to be less efficient in neutralization. This information advances our understanding of these unusual antibodies in ways that can be applied in the development of effective vaccines for camelids. more »

Objective—To determine humoral responses to an equine West Nile virus (WNV) vaccine in healthy alpacas and llamas and compare responses in alpacas and llamas with responses in horses. Design—Clinical trial. Animals—28 alpacas, 56 llamas, and 16 horses. Procedure—Horses received 2 vaccinations at 4- week intervals, and alpacas and llamas received 3 vaccinations at 3-week intervals. Fifty-five llamas received a fourth vaccination 3 weeks after the third. Blood samples were collected immediately prior to each vaccination, 3 weeks after the last vaccination for alpacas and llamas, and 4 weeks after the last vaccination for horses and tested for virus-neutralizing antibodies. Samples from 29 randomly selected vaccinated llamas were used. Results—None of the animals developed any local or systemic adverse reactions. Four of 28 (14%) alpacas, 4 of 29 (14%) llamas, and 7 of 16 (44%) horses were seropositive 3 (llamas and alpacas) or 4 (horses) weeks after administration of the first vaccination; 27 of 28 (96%) alpacas, 26 of 29 (90%) llamas, and 15 of 16 (94%) horses were seropositive after administration of the second vaccination; and all 28 alpacas and 28 of 29 (97%) llamas were seropositive 3 weeks after administration of the third vaccination. Conclusions and Clinical Relevance—Results suggest that vaccination with the equine WNV vaccine is safe in alpacas and llamas. Administration of 3 vaccinations generally resulted in virus-neutralizing antibody titers similar to those observed following 2 vaccinations in horses; however, because it is not known what antibody titer would be protective against clinical WNV disease in alpacas or llamas, we cannot conclude that the vaccine was efficacious. more »

Blood transfusion would be a potential source in alpacas, however unlikely. The other method that West Nile Virus can be transmitted – at least in horses and in people – is transplacentally, which means a pregnant mother who has been infected can infect the unborn child. Transmission by blood transfusion or across the placenta have not been demonstrated in camelids. more »

The first reports of WNV clinical disease in camelids occurred during the 2002 epizootic, which happened to be a particularly bad year for WNV in other species as well, accounting for 284 human deaths and countless bird and horse losses. Confirmation of camelid clinical neurologic disease resulting from WNV infection was made from post-mortem testing using immunohistochemistry and reverse- transcriptase polymerase chain reaction (PCR) from cases in Ohio and Iowa, respectively. more »