Testing for clinical anaemia caused by Haemonchus spp. in goats farmed under resource-poor conditions in South Africa using an eye colour chart developed for sheep

Abstract

A novel clinical assay for the assessment and subsequent treatment of Haemonchus infection in sheep to slow down the development of anthelmintic resistance — the FAMACHA © system — has been developed, tested and validated in South Africa. The system is based on a colour chart with five colour categories depicting varying degrees of anaemia that are compared with the colour of the mucous membranes of the eyes of sheep. The animal is then scored from severely anaemic (pale) through anaemic to non-anaemic (red) and those animals considered in danger of succumbing to the effects of haemonchosis are treated. This method was tested in goats farmed under resource-poor conditions in South Africa. Analyses in goats performed during the summers of 1998/1999 and 1999/2000 show a test sensitivity of 76 and 85%, respectively, meaning that the system may be used to identify correctly 76–85% of those animals in need of treatment with an anthelmintic. However, the test specificity remains low at 52–55%. This means that a large proportion of those animals that would not require treatment would in fact be treated. However, when the use of the FAMACHA © system is compared with conventional dosing practices where all the animals are treated, using the FAMACHA © system would result in a large proportion of the animals being left untreated. The untreated animals are then able to deposit the eggs of anthelmintic-susceptible worms on the pasture, while the treated ones should pass very few ova, given an effective anthelmintic. This maintains a reservoir of susceptible larvae in refugia, and should slow down the development of anthelmintic resistance. The validation of the FAMACHA © system for goats for use by resource-poor farmers, which this paper describes, may have wide application in the tropics and subtropics of sub-Saharan Africa and elsewhere.