Prospective characterization of the clinicopathologic and immunologic features of an immunodeficiency syndrome affecting juvenile llamas

Prevalence of Mycoplasma haemolamae infection in Peruvian and Chilean llamas and alpacas

Mycoplasma haemolamae is a hemotropic mycoplasma that affects red blood cells of llamas (Lama glama) and alpacas (Lama pacos). It is variably associated with anemia, and most infections are subclinical. Development of a polymerase chain reaction assay has facilitated detection of this infection in llamas and alpacas in the United States and other countries. Whether the infection occurs in camelids in South America has previously been unknown. The current study documents a 15.8% infection rate among 76 Peruvian llamas, a 19.3% infection rate among Peruvian alpacas at one site, and a 9.26% infection rate in 108 Chilean alpacas from selected herds. All of the camelids tested appeared to be clinically healthy. No gender or species predilection was found. Only 1 positive camelid younger than 18 months was found. Infection is not associated with anemia, and the mean packed cell volume (PCV) in positive Peruvian camelids was slightly higher than the mean PCV in negative Peruvian camelids. In the Chilean alpacas, the positive alpacas had a slightly lower PCV than the negative alpacas, although the mean PCV was not in the anemic range in any of the groups.

Use of a polymerase chain reaction assay to study response to oxytetracycline treatment in experimental Candidatus Mycoplasma haemolamae infection in alpacas

OBJECTIVE

To develop a PCR assay for Candidatus Mycoplasma haemolamae (CMhl) infection in alpacas and use it to study the efficacy of oxytetracycline treatment and development of a subclinical carrier state.

ANIMALS

8 healthy adult alpacas.

PROCEDURES

Alpacas initially had negative results for CMhl in blood samples via PCR assay and were experimentally infected with CMhl; 4 were treated with oxytetracycline, and 4 were not treated. All were monitored regularly via PCR assay, blood smear examination, PCV, rectal temperature, and physical examination. At 6 months after treatment, all alpacas were immunosuppressed by administration of dexamethasone and tested for CMhl.

RESULTS

7 of 8 alpacas had positive PCR assay results 4 to 6 days after experimental infection. When organisms were detectable on a blood smear, they were seen 2 to 6 days after positive results of PCR assay. Infection was often associated with mild anemia that was usually transient. No alpacas became hypoglycemic. Oxytetracycline treatment was not associated with faster clearance of organisms or resolution of anemia, and 4 of 4 treated alpacas still had positive results of PCR assay when immunosuppressed 6 months later; 0 of 3 nontreated alpacas had positive results of PCR assay following immunosuppression. Transient fever was detected in 3 alpacas during immunosuppression.

CONCLUSIONS AND CLINICAL RELEVANCE

The PCR assay was more sensitive than blood smear examination for detection of infection. Clinical signs, anemia, and fever were not necessarily associated with infection. Oxytetracyline administration did not consistently clear CMhl infection. Although treated with oxytetracycline, infected alpacas remained chronic carriers.

Development of ELISAs for the measurement of IgM and IgG subclasses in sera from llamas (Lama glama) and assessment of the humoral immune response against different antigens

Members of the Camelidae family possess a functional class of antibodies devoid of light chains (known as heavy chain antibodies, HCAbs). Three IgG isotypes have been identified (IgG(1), IgG(2) and IgG(3)); IgG(2) and IgG(3) are HCAbs whereas the IgG(1) has the conventional structure. Different subtypes of IgG(1) (IgG(1a) and IgG(1b)) and IgG(2) (IgG(2a), IgG(2b) and IgG(2c)) have been classified according to variations in the amino acids sequence of the hinge region. The single variable domain of HCAbs has been referred as VHH. Until now, the relative amount of each subclass has been inferred, but the lack of highly specific antibodies against HCAbs has been a limitation for their quantification. In a previous work, we produced specific polyclonal antibodies against IgG(2a), IgG(2b), IgG(2c) and IgG(3) by immunizing rabbits with synthetic and recombinant peptides corresponding to their hinge region. In this work we produced specific antisera against llama IgM and IgG(1). The anti-IgG(1) serum was obtained by immunizing rabbits with a recombinant fusion protein formed by GST fused to the CH(1) domain of the IgG(1). The anti-IgM serum was obtained by immunizing rabbits with IgM heavy chain. All these antisera were useful for the development of ELISAs for the measurement of IgM, total IgG and IgG subclasses. Sera from llamas (n=20) analyzed by ELISA gave the following values of immunoglobulins: IgG(1)=6.168+/-1.628 mg/ml; IgG(2)=0.684+/-0.310 mg/ml; IgG(3)=1.232+/-0.410 mg/ml; total IgG=8.933+/-1.815 mg/ml and IgM=1.027+/-0.308 mg/ml. These results indicate that HCAbs represent almost 25% of total IgG and the IgG(3) subtype is the predominant HCAb. We also analyzed the primary humoral immune response after immunization llamas with different antigens (BSA, BSA-DNP and dextran). Although it has been described that a few VHH clones are very efficient in the interaction with haptens, in this case the response against DNP was characterized by a delayed appearance of HCAbs in comparison with that of IgG(1). No anti-dextran response was observed in any of the isotypes analyzed.

Camelid immunoglobulins and their importance for the new-born--a review

Camelid immunoglobulins differ from all other known antibodies and contradict all common theories on antibody diversity. It was demonstrated that up to 75% of all serum proteins are immunoglobulin G (IgG) molecules lacking light chains. IgG2 and IgG3, which only consist of heavy chains, have a low molecular weight which improves their biodistribution and allows a better tissue penetration. Of special importance is the long complementary determining region (CDR) loop which inserts deep into the active site of an enzyme. This binding property was only observed in experiments to gain structural data and to point out the extraordinary value of heavy chain antibodies as biochemical and pharmacological tools. The acquisition and absorption of adequate amounts of colostral immunoglobulins are essential to the health of the neonate. Pre-colostrum serum IgG levels in camelids are low, with concentrations of 0.26 +/- 10.23 mg/ml. Maximum IgG levels are reached after 24 h and kept at a plateau with concentrations of 24.52 +/- 8.8 mg/dl. IgG concentrations above 10 mg/ml indicate a successful passive transfer. IgG levels decline after 2-5 weeks and a marked increase is observed between 1 and 2 months, indicating that the immune system of the neonate has started to mature. A number of different tests are available for the assessment of IgG serum levels. Single radial immunodiffusion (SRID) is the only method that specifically measures serum IgG concentrations. It is a reliable assay to test failure of passive transfer (FPT). FPT is a major factor in neonatal mortality in camelids, but very little has been published so far. Therapeutic administration of colostrum will provide passive protection against infectious diseases for a 2-3-week period of risk, and the intravenous administration of 20-40 ml of camelid plasma helps to combat FPT.

Intraocular melanoma in an alpaca

A case of primary intraocular melanoma in an alpaca is reported. This patient also presented with a mild normocytic, normochromic anemia and hypoproteinemia. These can be markers of an immunodeficiency syndrome associated with llamas. Although this patient did not appear to have clinical signs of this syndrome, its presence needed to be ruled out as animals affected with this syndrome are subject to recurrent severe debilitating diseases and death. To our knowledge, intraocular melanoma has not been previously reported in an alpaca.

Flow cytometric analysis of an immunodeficiency disorder affecting juvenile llamas

The present study was undertaken to characterize the immune system of llamas and alpacas and establish the basis for an immunodeficiency disorder affecting juvenile llamas. Flow cytometric (FC) analysis of the immune system with a panel of monoclonal antibodies (mAbs) revealed the immune system of llamas and alpacas is similar in leukocyte subset composition to that in ruminants. Peripheral blood mononuclear cells in adults are comprised of surface immunoglobulin (sIg(+)) B-cells (31%+/-8 S.D.), alphabeta T-cells (27%+/-12 S.D.), WC1(+) gammadelta T-cells (16%+/-11 S.D.), and 5-16% monocytes. In contrast to cattle, goats, and sheep, however, the frequency of WC1(+) gammadelta T-cells is not high in juveniles but similar to the frequency in adults. Also, sIg(+) B-cells are present in high concentration in juveniles (43%+/-11 S.D. ). Expression of major histocompatibility class II molecules on resting T-cells was low or absent. Comparative analysis of peripheral blood lymphocyte composition in normal juvenile llamas and llamas presenting with the signs of the juvenile llama immunodeficiency syndrome (JLIDS) revealed the concentration of B-cells is extremely low (1-5%) in affected animals. The findings suggest JLIDS is attributable to an autosomal recessive genetic defect in the development of B-cells.

Immunodiagnostic testing in horses

Technologic advances in immunodiagnostic testing have enhanced our understanding of the pathogenesis of a broad array of diseases, including infectious diseases, immunodeficiency disorders, and immune-mediated disorders. If applied rationally, with an understanding of the questions the tests answer as well as the limitations that constrain their use, these tests can serve as valuable aids in the diagnosis and management of equine diseases.