Worm burden in concurrent infections with H. contortus and T. brucei in Nigerian WAD goats from the humid zone. Animals were segregated into low and high FEC producers, following escalating (immunising) infections, as described in the legend to Figure 4. All the animals were treated with an anthelmintic (fenbendazole) on day 61 (d61) to remove the escalating (immunising) infection and then half of each group or FEC phenotype (9 goats in each, total = 18) were infected with 50 × 10⁶ trypanosomes (Tryp +ve, animals). The other half remained trypanosome-naive (No tryps). Seven days later, on d68, all the animals (n = 36) were challenged with 3000 L3 of H. contortus. The figure shows that in those animals which harboured heavy worm infections initially, based on FEC (the high FEC phenotype) prior to anthelmintic abbreviation of immunising infections, subsequent challenge with H. contortus and concurrent infection with T. brucei, resulted in significantly heavier worm burdens compared with similarly treated animals, which produced initially only low FEC. This shows that the trypanosome-elicited increase in worm burdens was confined to the high FEC (poor responder) goats. The y-axis indicates the value of the mean worm burden of relevant groups. For further details see Chiejina et al. [16].