The mare reproductive loss syndrome and the eastern tent caterpillar: a toxicokinetic/statistical analysis with clinical, epidemiologic, and mechanistic implications.

This research investigates the mare reproductive loss syndrome (MRLS), a condition affecting horses which prompted epidemics of fetal loss and other disorders in Kentucky in 2001. The study utilized toxicokinetic/statistical analysis to show evidence of a causal connection between the eastern tent caterpillars (ETCs) and MRLS.

Background of the Study

• The study was prompted by the outbreak of mare reproductive loss syndrome (MRLS) in central Kentucky during 2001 that led to sudden, significant instances of early and late fetal losses, pericarditis, and unilateral endophthalmitis.
• The purpose of this study was to investigate a suspected link between the outbreak and exposure to eastern tent caterpillars (ETCs).

Toxicokinetic/Statistical Analysis and Experimental Procedures

• The researchers performed the toxicokinetic/statistical analysis of field and experimental MRLS data.
• The specific experiment involved the administering of different daily doses of ETCs (100g or 50g, or 100g of irradiated caterpillars) to pregnant mares, observing the subsequent abortions.
• Applied statistical modeling (accelerated failure time or AFT analysis) was used to fit the experimental data.
• The times to first abortion (deemed as “lag time”) and abortion rates were measured, revealing a dose-dependent relationship, with increased doses leading to decreased lag times and higher abortion rates.

Interpretation of Findings

• The calculated results allowed the researchers to interpret the abortion data in terms of “intubated ETC equivalents”.
• Analysis suggested that mares’ exposure to ETCs in the field during the 2001 outbreak in central Kentucky seemed to have begun around April 27 and gradually increased until reaching a peak.
• It provides a mathematical model that accounts for many aspects of MRLS’s epidemiology, clinical presentations, and manifestations.

Implications and Conclusion

• This study has implications for the basic mechanisms underlying MRLS and supports the hypothesis that MRLS is caused by exposure to ETCs.
• The analysis also indicates that higher levels of ETC exposure would create intense outbreaks of MRLS, localized in both time and place to ETC dispersion, as seen in the 2001 Kentucky instances.
• However, with less intense exposure, the lag time before noticeable effects is longer, and abortions tend to occur over a longer time frame and potentially out of phase with ETC exposure, making the connection between the syndrome and the caterpillars less obvious.