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Parasite co-infections show synergistic and antagonistic interactions on growth performance of East African zebu cattle under one year - PubMed

. 2013 Dec;140(14):1789-98.

doi: 10.1017/S0031182013001261. Epub 2013 Sep 4.

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Free PMC article

Parasite co-infections show synergistic and antagonistic interactions on growth performance of East African zebu cattle under one year

S M Thumbi et al. Parasitology. 2013 Dec.

Free PMC article

Abstract

The co-occurrence of different pathogen species and their simultaneous infection of hosts are common, and may affect host health outcomes. Co-infecting pathogens may interact synergistically (harming the host more) or antagonistically (harming the host less) compared with single infections. Here we have tested associations of infections and their co-infections with variation in growth rate using a subset of 455 animals of the Infectious Diseases of East Africa Livestock (IDEAL) cohort study surviving to one year. Data on live body weight, infections with helminth parasites and haemoparasites were collected every 5 weeks during the first year of life. Growth of zebu cattle during the first year of life was best described by a linear growth function. A large variation in daily weight gain with a range of 0·03-0·34 kg, and a mean of 0·135 kg (0·124, 0·146; 95% CI) was observed. After controlling for other significant covariates in mixed effects statistical models, the results revealed synergistic interactions (lower growth rates) with Theileria parva and Anaplasma marginale co-infections, and antagonistic interactions (relatively higher growth rates) with T. parva and Theileria mutans co-infections, compared with infections with T. parva only. Additionally, helminth infections can have a strong negative effect on the growth rates but this is burden-dependent, accounting for up to 30% decrease in growth rate in heavily infected animals. These findings present evidence of pathogen-pathogen interactions affecting host growth, and we discuss possible mechanisms that may explain observed directions of interactions as well as possible modifications to disease control strategies when co-infections are present.

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Figures

Fig. 1.
Fig. 1.

Growth trajectories of the 455 calves that completed the one year observation time. The blue dots are individual's weights recorded and the grey lines connect repeated measures for each calf. Routine weight measurements were done from birth up to week 31 of age, and thereafter at the final visit done at week 51 before leaving the study.

Fig. 2.
Fig. 2.

Schematic diagram showing associations between average daily weight gain and different infections and co-infections. Negative associations with ADWG have the sign (−ve), and positive (+ve). All single infections have a negative effect on ADWG. The size of the effect expressed as a percentage of the average growth rate in uninfected animals is shown in blue. Co-infections of T. parva and A. marginale have a significant negative effect (synergistic) on ADWG, above the sum of their individual effects. Animals co-infected with T. parva and T. mutans have a significant positive interaction (antagonistic), with average growth rates in coinfected animals higher than in animals infected with T. parva only. The model controls for the non-infectious factors. (ns) = non-significant effect.

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