Intestinal Nematode Parasites of Vertebrates

Interactions between 11

Intestinal Nematodes and

Vertebrate Hosts

M.V.K. Sukhdeo,

1

S.C. Sukhdeo

2

and A.D. Bansemir

3

(^1) Department of Ecology, Evolution and Natural Resources, Rutgers
University, 14 College Farm Road, New Brunswick, NJ 08901, USA;
(^2) Department of Ecology, Evolution and Natural Resources, Rutgers
University, 84 Lipman Drive, New Brunswick, NJ 08901, USA;
(^3) Division of Life Sciences, Rutgers University, 604 Allison Road,
Piscataway, NJ 08904, USA

Introduction

The phylum Nematoda (roundworms) is one of the largest groups in the

animal kingdom, and some estimates suggest that four out of every five

metazoans are nematodes (Bongers and Ferris, 1999). Gastrointestinal

nematodes represent only a tiny subset of this vast assemblage, but,

because of the severe medical and economic consequences of human

infection (> 3 billion people infected (Montresoret al., 1998)), we know a

lot about these worms. Members of this group are obligate parasites that

spend all, or part, of their lives in the guts and associated organs of their

hosts. Entry into the vertebrate host is usually via oral ingestion or skin

(percutaneous) penetration, and the worms often travel long distances in

their hosts to reach their adult sites. Adult worms typically end up in

narrow and precise microhabitats within the gut, even though most of the

intestinal habitat tends to be vacant of competing parasite species (Rohde

and Hobbs, 1986). Interspecific competition and/or resource-dependent

mechanisms have been proposed to explain this phenomenon (Holmes,

1973; Rohde, 1979, 1992), but there have been few rigorous tests of these

ideas. In addition, parasite decisions on the best locations within the

gut are not independent of higher-level effects of life history and the

constraints of phylogeny. This chapter will focus on the basic strategies

used by gastrointestinal nematodes to get to their habitats in the gut

of vertebrate hosts. Studies on the proximate mechanisms of habitat

selection behaviour and the role of resources (food, attachment and

mates) in parasite strategic decisions will be used to re-examine some

traditional hypotheses on the behaviour of these worms.

CABInternational2002.The Behavioural Ecology of Parasites
(eds E.E. Lewis, J.F. Campbell and M.V.K. Sukhdeo) 223