The immunological response of foals to Rhodococcus equi: a review.

The research article discusses the immune response of horses, particularly foals, to Rhodococcus equi, a bacterium that can cause pneumonia. It notes that there are higher levels of antibodies to R. equi in horses from diseased farms compared to those from healthy farms, and even suggests the severity of the disease can be determined by the level of specific antibodies in the horse’s system. The study also highlights the application and results of various tests to detect infection. The potential for treatment options, such as vaccination and passive immunization, have also been assessed, although with limited success.

Understanding Rhodococcus equi Infection in Horses

• Rhodococcus equi is a bacterium that is commonly present in the intestines of horses, irrespective of their age. This bacterium is frequently seen in horses from diseased farms and can cause a severe form of pneumonia. The level of antibodies specific to R. equi, as the paper suggests, could indicate the severity of the infection.

Occurrence and Severity of Disease

• The study shows that horses from diseased farms had a stronger antibody response when compared to horses from healthy farms. The more severe reactions were associated with a higher bacterial presence.
• Methods such as ELISA (Enzyme-Linked Immunosorbent Assay) were used to measure the levels of IgG antibodies during natural infection. A significant increase in these antibodies was observed during natural infection due to R. equi.
• The researchers noted that the severity of pneumonia could be correlated with lower specific antibody responses.

Detection Methods and Immune Response

• Various tests, including complement fixation, indirect immunofluorescence, ELISA, lymphocyte blastogenesis, and skin testing, have been used to detect evidence of infection by R. equi and to measure the immunological response.
• The response following experimental infection could be detected with these tests, indicating the presence of an immunological response to R. equi.

Potential Treatments

• Very little research has been conducted on developing a vaccine against R. equi infection. The results of such studies have been less than encouraging.
• The study also reports that passive immunization – the transfer of active immunity from one individual to another – has shown some success in treating R. equi infection.
• However, administration of immune leucocyte extracts did not affect the morbidity or mortality rates of the infection.

Conditions Favoring Infection

• The article suggests that infection with R. equi may not occur unless certain conditions are met. Despite its widespread distribution, the disease caused by R. equi is relatively infrequent. This points to the possibility that R. equi may only cause infection in situations of a high infectious challenge, immunological immaturity or deficiency in the host, or a genetic predisposition.