Lower airway disease, now and in the future

Genetics of Equine Respiratory Disease

Genetic factors influence the development of guttural pouch tympany, recurrent laryngeal neuropathy, severe equine asthma, exercise-induced pulmonary hemorrhage, and possibly also some malformations and infectious diseases of the respiratory tract. The current data suggest that most of these diseases are complex, resulting from the interaction between several genes and environmental factors. To date, no specific genes or causative mutations have been identified that would allow the development of practical genetic tests. In the future, genetic profiling panels, based on multiple genetic markers and environmental risk factors, may allow identification of individuals with an increased genetic risk.

Alkaline phosphatase activity in airway fluid obtained by tracheal wash from adult horses

BACKGROUND

Collection of fluid from the lower respiratory tract (LRT) plays an important role in both the pathophysiological investigation and diagnosis of respiratory tract disease. Enzymes such as ALP are, among others, indicators of cell damage or death, type II pneumocyte proliferation, and neutrophil invasion, and have been useful as biomarkers of respiratory disease in other species.

OBJECTIVES

The purpose of this study was to determine and compare tracheal wash (TW) ALP activity in healthy horses and horses with LRT inflammation (LRTI) determined by TW cytology profile.

METHODS

Tracheal washes were collected from asymptomatic adult geldings to measure ALP activity. The horses were allocated to the healthy group or the group with LRT inflammation based on differential leukocyte counts of TW preparations. Horses with > 20% neutrophils and > 1% eosinophils were allocated to the LRTI group, the horses with < 20% neutrophils and < 1% eosinophils were the controls.

RESULTS

Tracheal wash ALP activity, measured using a semiautomatic chemistry analyzer, was statistically significantly higher in 18 horses with LRTI (18.9 ± 11.2 × 10(3) U/L) than in healthy horses (10.3 ± 5.9 × 10(3) U/L) (P = .021).

CONCLUSIONS

Determining tracheal wash ALP activity is a simple, inexpensive and safe technique that can be used to facilitate the early diagnosis of equine respiratory disease, since it is higher in asymptomatic adult horses with a TW cytology profile consistent with LRT inflammation than in healthy adult horses with a normal TW cytology profile.

Genetics of upper and lower airway diseases in the horse

Genetic predispositions for guttural pouch tympany, recurrent laryngeal neuropathy and recurrent airway obstruction (RAO) are well documented. There is also evidence that exercise-induced pulmonary haemorrhage and infectious diseases of the respiratory tract in horses have a genetic component. The clinical expression of equine respiratory diseases with a genetic basis results from complex interactions between the environment and the genetic make-up of each individual horse. The genetic effects are likely to be due to variations in several genes, i.e. they are polygenic. It is therefore unlikely that single gene tests will be diagnostically useful in these disorders. Genetic profiling panels, combining several genetic factors with an assessment of environmental risk factors, may have greater value, but much work is still needed to uncover diagnostically useful genetic markers or even causative variants for equine respiratory diseases. Nonetheless, chromosomal regions associated with guttural pouch tympany, recurrent laryngeal neuropathy and RAO have been identified. The association of RAO with other hypersensitivities and with resistance to intestinal parasites requires further study. This review aims to provide an overview of the available data and current thoughts on the genetics of equine airway diseases.