Acute-phase Proteins and Interleukin-6 (IL-6) in Cattle Infected with Subclinical Parasitic Infections

Background: The acute phase response (APR) has been well documented for clinical infections. There are relatively few reports regarding the potential uses of acute phase proteins (APP) for the recognition of subclinical infection. Until now, There have been no reports published on the development of the APR in subclinical infection with parasites. Haptoglobin (Hp) and serum amyloid A (SAA) are important APPs for cattle. Interleukin-6 (IL-6) is considered a major immune and inflammatory mediator and the principal regulator of most APPs. This study was carried out to ascertain the levels of SAA, Hp and IL-6 in cattle infected with low levels of various parasites. Materials, Methods & Results: Thirty six slaughtered cattle (20 male, 16 female) of varying ages were used. Clinical findings such as pain, redness, slackness, diarrhoea or fever were not seen in these cattle. Blood samples were taken into vacutainers without heparin during slaughter, the internal organs of the cattle were examined postmortem for possible infections and faecal samples were collected. For detection, Benedect’s sedimentation was used for trematode infections, saturated water flotation was used for cestode and nematode infections, and the Baermann Wetzel method was used for lungworm infections. A total of 28 cattle with parasitic infection were evaluated as the study group and eight parasitologically free cattle were used as the control group. In the study group, 12 of the 28 cattle were infected with Eimeria sp. only, 10 with Trichostrongylidae only, one with hydatid cysts only and five with mixed parasites (Trichostrongylidae + Eimeria sp. in one animal, Trichostrongylidae + hydatid cyst in two animals, Trichostrongylidae + Moniezia sp. in two animals). Trichostrongylidae and Eimeria sp. infections were found at low levels. Serum amyloid A, Hp and IL-6 levels in the serum samples were analysed using the enzyme linked immunosorbent assay method. In the present study, levels (mean ± standard error) of SAA and Hp were significantly (P < 0.01) lower (1.83 ± 0.52 μg / mL and 0.77 ± 0.15 ng / mL, respectively) in the study group compared with the those of the control group (4.84 ± 0.51 μg / mL and 3.87 ± 0.91 ng / mL, respectively). The serum concentration of IL-6 in the study group was significantly (P < 0.01) higher than that in the control group. This elevated level was higher in cattle infected with Eimeria sp. and mixed parasites (P < 0.01). Serum SAA levels of cattle infected with Eimeria sp. and Trichostrongylidae were statistically lower compared with those of the control group (P < 0.05). Discussion: Acute phase proteins are specific indicators of tissue damage. Therefore, these proteins are an important parameter in terms of herd health and the monitoring of treatment during infections in veterinary medicine. Subclinical parasitic diseases are an important cause of production losses in cattle, even though this condition is very often found in field conditions. In the present study, Hp and SAA levels were significantly lower and the level of IL-6 significantly higher in cattle infected with a low level of parasites when compared with healthy animals. The determination of serum Hp and SAA concentrations may be helpful clinically to monitor concomitant immunity and to evaluate animal health. The results indicate that measurement of SAA, Hp and IL-6 concentrations may be a valuable in combination for monitoring cattle infected with subclinical parasitic infections.