Skin lesions and cattle hide damage from Haematobia irritans infestations.

The horn fly Haematobia irritans L. (Diptera: Muscidae) has recently spread to Argentina and Uruguay and is believed to cause damage to cattle hides. Four groups of ten Holstein steers each were maintained for 58 weeks under different infestation levels with H. irritans to determine if it was the cause of this problem. Hides (chrome tanned) from steers maintained under minimum infestation level had 4.7 +/- 3.8% of the area damaged. Maintaining the steers under low H. irritans level for the last 44 days of the trial using insecticidal ear-tags, resulted in 29.5 +/- 15.8% of hide area being damaged. Steers that were treated with 5% cypermethrin pour-on, when the H. irritans population was close to 50 flies, showed that 31.3 +/- 16.6% of hide area was injured, and 46.6 +/- 12.8% of damaged hide area was found in hides from non-treated steers. Significant differences were found between mean hide damage from steers maintained continuously under low H. irritans infestation levels and all other groups. Hyperaemia was significantly lower in the skin of steers under low H. irritans infestation level than in the skins of non-treated steers and steers maintained under low-level infestations for the final 44 days. Eosinophil and mononuclear cell infiltration was significantly lower when the population of H. irritans was less than six per steer than when the population was more than 100 flies per steer. Low numbers of Stomoxys calcitrans were found in all groups, but most hide damage was presumed due to H. irritans.

Evaluation of natural Psoroptes ovis (Acarina: Psoroptidae) soluble proteins as candidate vaccine immunogens.

In this study potential vaccine candidate immunogens were identified and evaluated in a vaccine challenge trial. Calves vaccinated with a partially purified fraction of Psoroptes ovis-soluble proteins had 8 of 14 calves free of palpable lesions 8 wk after a challenge infestation. A self-grooming behavioral response elicited by a pruritic immediate-type allergic reaction was believed to be an effector in protecting the vaccinated calves from a clinical P. ovis infestation.

Antigen-specific lymphocyte proliferative responses in vaccinated and Hypoderma lineatum-infested calves.

Cattle infested with the common cattle grub, Hypoderma lineatum (Villers) develop specific humoral antibodies and a cellular immune reaction, defined by delayed-type hypersensitivity, to purified H. lineatum proteins. This investigation was designed to study the antigen-specific bovine lymphocyte response to hypodermin A (HyA), a serine protease of larval first-instar H. lineatum. Calves were vaccinated with either native or denatured HyA, and challenge-infested with H. lineatum. The kinetic development of a cellular immune response to HyA was monitored during vaccination and infestation. The HyA-specific responses were highly variable and weak during vaccination and infestation. Although HyA-specific lymphocyte blastogenic responses were observed, no correlation was noted between the magnitude of antigen-specific, peripheral lymphocyte proliferation and larval mortality. In striking contrast to responses observed during infestation, intense HyA-specific lymphocyte responses were observed with 3 calves 6 months after recovery from infestation. In addition, those responses were further heightened by a 250 micrograms booster injection of pure HyA.

Dexamethasone-induced bovine T-lymphocyte suppression and the effect upon susceptibility to sheep scab mite (Acari: Psoroptidae) infestation.

The synthetic glucocorticoid dexamethasone was used to suppress bovine T-lymphocyte function. Dexamethasone-treated animals were challenged with Psoroptes ovis (Hering) to determine if the immunosuppressive treatment would normalize susceptibility to infestation. Dexamethasone suppressed T-lymphocyte function and anti-P. ovis antibody production, and delayed the onset of scab lesions. All animals were not equally susceptible to infestation as a result of dexamethasone treatment. These data further support the importance of anti-P. ovis antibody in colonization of cattle by P. ovis and the pathology associated with scab mite infestation.

Effects of dexamethasone on selected parameters of the bovine immune system.

The synthetic glucocorticoid, dexamethasone, has been used by investigators studying bovine immune mechanisms to either exacerbate infectious processes or stimulate stress-induced steroid-influenced immunosuppression. Considerable differences exist in the literature concerning the effect of dexamethasone on the bovine immune response. The purpose of our study was to clarify the reported effects of dexamethasone on bovine T-lymphocyte function. Therefore, we designed experiments to evaluate cellular and humoral aspects of the bovine immune response under the influence of dexamethasone. The experiments took into consideration the pharmacokinetics of dexamethasone and optimal and suboptimal doses of selected mitogens. The data suggest little variation in hematological parameters that occurred with the administration of dexamethasone. Leukocyte counts were slightly elevated at two observations, and this was believed to be the result of an increase in peripheral blood neutrophils. T-lymphocytes (erythrocyte rosetting) were not selectively depleted. However, suppression of T-lymphocyte function was noted, particularly in response to suboptimum doses of phytohaemagglutinin (PHA) and Concanaval in A (Con A). Antibody production to the T-dependent antigen, KLH, was suppressed in those animals receiving dexamethasone. These data suggest that the immunosuppressive effect of dexamethasone in the bovine is dependent upon the dose of dexamethasone administered, the pharmacological level of dexamethasone in vivo, physiological adaptation of the host, mitogen dose used in evaluation, and the time of evaluation post drug administration. The study points out the importance of considering these variables when interpreting the effects of dexamethasone on the bovine immune response.

Humoral and cellular immunoresponsiveness of stanchioned cattle infested with Psoroptes ovis.

Bovine scabies in a clinical problem during the cool autumn and cold winter months. In south Texas it is necessary to stanchion animals in order to elicit patent infestation during summer months. Environmental factors and grooming have been purported to account for summer resistance to infestation. However, stanchioned animals exhibit varied levels of susceptibility to infestation, suggesting that the noted variability may be influenced by the host immune response. In this study, animals were infested with Psoroptes ovis while in stanchions. The development of anti-P. ovis antibody activity was measured by the enzyme-linked immunosorbent assay and cellular immune function was monitored with mitogens and P. ovis antigens. A correlation was noted between the development of anti-P. ovis antibody activity and the increase in mite numbers and dermatitis. Coincident with the developing infestation was a suppression of T-cell function that appeared to be stress-related as a result of stanchioning. A working hypothesis is presented that attempts to correlate the developing humoral response and the depressed T-cell response with both an increasing dermatitis and mite population.

Development and decline of serum antibody activity to Psoroptes ovis antigens in infested cattle in an endemic and nonendemic scabies area of Texas.

The serum antibody activity to Psoroptes ovis antigens, as determined by enzyme-linked immunosorbent assay (ELISA), was monitored during the development and decline phase of scabies in cattle herds under feedlot conditions in an endemic (Bushland) and a nonendemic (Kerrville) scabies area of Texas. The infestations were initiated by exposing six calves in each of the herds to P. ovis and allowing the infestations to spread to other members of the herd. The cattle in the endemic area developed more lesions and a higher incidence of the disease than did the cattle in the nonendemic area; also, there were more cattle with specific serum antibody activity in the Bushland herd than in the Kerrville herd at the peak of the infestations (late January--early February). As infestations declined because of summer latency, the number of calves with specific serum antibody activity declined in both herds. Specific serum antibody activity disappeared in the Kerrville cattle when P. ovis was no longer detected. However, specific serum antibody activity was still detected in some of the Bushland cattle in late summer (August) and fall (October) examinations, when low numbers of P. ovis were detected. These results indicate that the ELISA would be very useful in detection of specific serum antibody activity in lightly infested calves, especially during the developmental and decline phases of the disease.

Cross-reactivity between the house dust mite Dermatophagoides pteronyssinus and the mange mites Psoroptes cuniculi and P. ovis. I. Demonstration of antibodies to the house dust mite allergen Dpt 12 in sera from P. cuniculi-infested rabbits.

The cross-reactivity of the mange mites Psoroptes cuniculi (PC) and Psoroptes ovis (PO) antigens with the house dust mite Dermatophagoides pteronyssinus (DP) antigens has been studied. Cross-reactivity between mange mite and house dust mite antigens was demonstrated by both ELISA and immunoelectrophoresis by use of a sheep anti-DP antiserum. Both PC and PO were demonstrated to contain eight cross-reacting antigens. Sera from rabbits infested with PC were demonstrated to produce antibodies to the homologous immunogen, to PO antigens, and to DP antigens. Of the seven sera from infested rabbits tested, four were demonstrated to produce a strong antibody response to a major DP antigen Dpt 12, and two were demonstrated to produce a weak response that was judged empirically by double-diffusion analysis. Two sera were judged to react with the DP lipoprotein, Dpt 4. Sera from control rabbits did not demonstrate reactivity with any extract tested. Despite the detection of anti-Dpt 12 antibodies, however, an antigen corresponding to Dpt 12 was not detected in either PC or PO extracts. The findings that mange mite-infested rabbits produce antibodies that recognize DP antigens probably explain previous observations in which it was demonstrated that commercially obtained rabbit anti-immunoglobulin antisera contain anti-DP antibodies, a finding that suggests caution in the use of such reagents in studies designed to measure antibody responses to DP allergens.

Dermatopathology and immunity in experimental Psoroptes ovis (Acari:Psoroptidae) infestation of naive and previously exposed Hereford cattle.

Naive and previously exposed young Hereford cattle were infested with Psoroptes ovis and maintained in stanchions for 7 weeks. Skin biopsy samples were examined at 1, 2, 5, and 7 weeks after infestation was induced, compared with those from noninfested control calves, and correlated with changes in the mite populations and development of dermatitis. Gross and microscopic appearance of lesions were qualitatively similar in both groups of infested calves. The lesions occurred early in the previously exposed calves, but progressed slowly, whereas lesions in the naive calves appeared later, but were rapidly progressive. The basic histopathologic pattern was chronic exudative superficial perivascular dermatitis compatible with allergy. The mite populations on the naive calves revealed exponential growth and high fecundity, and reached high population densities, whereas mite populations on previously exposed calves had low growth rates and low fecundity and reached population densities 100 to 1,000 times less than those on naive calves. Seemingly, there was a hypersensitivity to mite antigens. The hypersensitivity response may have been a mechanism by which humoral immunity was delivered to the mite microenvironment and may have contributed to acquired resistance by controlling mite populations. The mechanism of population control seems to be related partially to decreased fecundity of female P ovis.

Systemic pathologic responses in experimental Psoroptes ovis infestation of Hereford calves.

Nine Hereford calves were infested with Psoroptes ovis and were allowed to develop clinical mange during a 9-week period. Blood, serum, and urine samples were obtained before and after calves were infested and were compared with those from 3 noninfested control calves. All calves were euthanatized and necropsied 9 weeks after they were infested. Gross and microscopic anatomic changes occurred only in the skin. Calves developed typical exudative dermatitis, the extent of which was dependent on population density of mites. Severely infested calves (50% to 70% of skin with dermatitis) developed a mild anemia and lymphopenia with marked neutropenia and variable eosinophilia. There were also increases in fibrinogen, gamma-globulin, and in vitro lymphocyte response to mitogen stimulation and decreases in anion gap cortisol, albumin, albumin/globulin ratio, and fractional Na clearance values. The severity of many of the changes could be correlated with the extent of dermatitis.

Development of serum antibody activity as determined by enzyme-linked immunosorbent assay to Psoroptes ovis (Acarina:Psoroptidae) antigens in cattle infested with P. ovis.

Calves infested with Psoroptes ovis (Hering, 1838) for the first time (naive) or previously infested calves were examined for serum antibody activity to P. ovis (obtained from rabbits) antigens by enzyme-linked immunosorbent assay (ELISA) to determine the temporal appearance of specific serum antibody activity. The development of the serum antibody activity to P. ovis antigens was then correlated with the development of lesions (% scab) and with changes in the number of P. ovis. The serum antibody activity [ELISA OD414 value (EODV) greater than 0.290] to P. ovis antigens in naive calves, in most cases, is first detected at the same time or slightly after the detection of mites and mite-caused lesions; and the development of specific serum antibody activity paralleled the increase in the P. ovis population and the percentage scab until 7 weeks post-infestation (PI). In previously infested calves, if serum antibody activity to P. ovis antigens was not already present from the previous infestation, specific serum antibody activity was detected at the same time and developed in a similar manner as in the naive calves. The serum antibody activity to P. ovis antigens could be detected after calves were relieved of their P. ovis burdens by pesticide treatment or after the P. ovis population began to decline when the calves were allowed to groom themselves. Serum antibody activity to P. ovis antigens was not detected in any of the control calves during the test period.

Effects of Psoroptes ovis (Acarina:Psoroptidae) on certain biochemical constituents of cattle serum.

Sera from Psoroptes ovis-infested calves were examined for 17 selected biochemical constituents to determine if P. ovis caused changes in any of these constituents. In order to recognize a scabies effect, there had to be a statistically significant (P less than or equal to 0.10) scabies exposure X time interaction and the changes in the biochemical constituents should have been correlated with the changes in the mite infestation. Five serum biochemical constituents fulfilled these criteria. Total protein, alpha-, beta-, and gamma-globulin were increased and total cholesterol was decreased at the peak of the scabies infestation. Precipitating antibodies to a P. ovis antigen were detected by immunodiffusion in some of the stored sera of the infested calves just after the peak of the infestation. Total protein, beta-, and gamma-globulin values were probably increased as a result of antibody production; alpha-globulin values were probably increased as a result of inflammation. As the scabies infestation declined, the mean values of all the above constituents from the infested calves, except cholesterol, began declining. Decreases in total cholesterol occurred, but they could not be entirely attributed to scabies. Examination of the serum biochemical constituents from a heavily infested calf that died during the test suggested that, in addition to antibody production and inflammation, kidney and liver damage may have occurred.