Helminth-associated changes in host immune phenotype connect top-down and bottom-up interactions during co-infection

Area of Science:

• Ecology
• Parasitology
• Immunology

Background:

• Host phenotypes change with parasite infections, mediating interactions between co-infecting parasites.
• Parasites like helminths induce physiological, morphological, and immunological changes, driving bottom-up (resource) and top-down (immune) interactions.
• These interaction types are often studied separately, but host phenotypic changes may reveal combined effects.

Purpose of the Study:

• To investigate how helminth infections influence host phenotypes and drive bottom-up and top-down interactions with co-infecting coccidia in African buffalo.
• To examine the role of host immunological and morphological changes in mediating parasite interactions.
• To assess the repercussions of these interactions on host fitness.

Main Methods:

• An anthelmintic treatment study was conducted on African buffalo (Syncerus caffer) infected with helminths and coccidia.
• Changes in host immunological (Th1/Th2) and morphological phenotypes were tracked following helminth clearance.
• Coccidia shedding, host body condition, and reproductive parameters were assessed.

Main Results:

• Clearance of Haemonchus induced a Th2 immune phenotype, while Cooperia clearance induced a Th1 phenotype.
• The Th2 phenotype increased coccidia shedding through simultaneous top-down and bottom-up effects, altering the intestinal environment.
• Higher coccidia shedding correlated with reduced host body condition, lower pregnancy rates, and delayed age at first pregnancy.

Conclusions:

• Top-down and bottom-up parasite interactions can co-occur and are influenced by host phenotypic changes.
• Tracking host phenotypes provides insights into complex parasite interaction pathways.
• Coccidia infection imposes significant condition and reproductive costs on hosts, exacerbated by helminth-induced host responses.