Effect of the topical administration of corticosteroids and tuberculin pre-sensitisation on the diagnosis of tuberculosis in goats

Background

Caprine tuberculosis (TB) is a zoonosis caused by members of the Mycobacterium tuberculosis complex (MTBC). Caprine TB control and eradication programmes have traditionally been based on intradermal tuberculin tests and slaughterhouse surveillance. However, this strategy has limitations in terms of sensitivity and specificity. Different factors may affect the performance of the TB diagnostic tests used in goats and, subsequently, the detection of TB-infected animals. In the present study, the effect of two of the factors that may affect the performance of the techniques used to diagnose TB in goats, the topical administration of corticosteroids and a recent pre-sensitisation with tuberculin, was analysed.

Methods

The animals (n = 151) were distributed into three groups: (1) a group topically treated with corticosteroids 48 h after intradermal tuberculin tests (n = 53); (2) a group pre-sensitised with bovine and avian purified protein derivatives (PPDs) 3 days before the intradermal tuberculin test used for TB diagnosis (n = 48); and (3) a control group (n = 50). All the animals were tested using single and comparative intradermal tuberculin (SIT and CIT, respectively) tests, an interferon-gamma release assay (IGRA) and a P22 ELISA.

Results

The number of SIT test reactors was significantly lower in the group treated with corticosteroids when compared to the pre-sensitised (p < 0.001) and control (p = 0.036) groups. In contrast, pre-sensitisation with bovine and avian PPDs did not cause a significant reduction in the number of SIT and CIT test reactors compared with the control group. In fact, a higher number of reactors was observed after the prior tuberculin injection in the pre-sensitised group (p > 0.05). No significant effect was observed on IGRA and P22 ELISA due to corticosteroids administration. Nevertheless, a previous PPD injection affected the IGRA performance in some groups.

Conclusions

The application of topical corticosteroid 24 h before reading the SIT and CIT tests can reduce the increase in skin fold thickness and subsequently significantly decrease the number of positive reactors. Corticosteroids used can be detected in hair samples. A previous pre-sensitisation with bovine and avian PPDs does not lead to a significant reduction in the number of intradermal tests reactors. These results are valuable in order to improve diagnosis of caprine TB and detect fraudulent activities in the context of eradication programs.

Detection of methicillin-resistant Staphylococcus aureus in Iberian pigs

AIMS

Iberian pigs are bred in Spain for the production of high-value dry-cured products, whose export volumes are increasing. Animals are typically reared outdoors, although indoor farming is becoming popular. We compared carriage of methicillin-resistant Staphylococcus aureus (MRSA) in Iberian pigs, raised indoors and outdoors, with intensively farmed Standard White pigs.

METHODS AND RESULTS

From June 2007 to February 2008, 106 skin swabs were taken from Iberian pigs and 157 samples from SWP at slaughterhouses in Spain. We found that Iberian pigs carried MRSA, although with a significantly lower prevalence (30/106; 28%) than SWP (130/157; 83%). A higher prevalence of indoor Iberian pigs compared with animals reared under outdoor conditions was not significant; however, all but one positive indoor Iberian pig samples were detected from one slaughterhouse. Overall, 16 different spa types were identified, with t011 predominating in all three animal populations. A subset of isolates was characterized by MLST. Most of these belonged to ST398. MRSA isolates from Iberian pigs presented a higher susceptibility to antibiotics than those isolated from SWP.

CONCLUSIONS

Despite limited contact with humans, pigs raised outdoors are colonized by an MRSA population that genetically overlaps with that of intensively farmed pigs, although antimicrobial resistance is lower.

SIGNIFICANCE AND IMPACT OF THE STUDY

To our knowledge, this is the first detection of MRSA in food animals raised in free-range conditions.