Hormonal effects on insects and other endoparasites in vitro

Abstract

Metamorphic and reproductive events in vertebrates and invertebrates are under endocrine control and are often correlated with developmental, behavioral, or reproductive changes in the parasites living in or on these hosts. This paper reviews selected examples of a) host hormone mediated influences on endoparasites in vivo, b) host hormone effects in vitro on protozoan, helminth, and insect endoparasites, and c) identifies possible relationships in hormone effects across parasite taxa. The significance of studies on endoparasites in vitro in relation to the impact of host hormones, antihelminthic, and prophylactic drugs on parasite growth and proliferation will also be addressed. A review of the literature indicates only limited studies have been done in vitro in an attempt to elucidate the bases of reported host hormone influences on endoparasites in vivo. Steroid hormones of hosts seem to stimulate growth, molting or encystment or both of helminth, insect, and protozoan parasites. Vertebrate steroids such as estrogen, testosterone, and progesterone had primarily reproduction- or growth-promoting effects or both on protozoan and nematode parasites. Insect ecdysteroids such as ecdysone, 20-hydroxyecdysone, and makisterone were the most widely studied steroids in vitro and induced growth or molting or both of cestode, nematode, and insect parasite larvae. Although juvenile hormone (JH III) stimulated growth in the protozoan and nematode parasites tested, the analogue methoprene and JH precursors, farnesal, farnesol, and farnesol methyl ether had various effects. Biogenic amines also varied in their effects on the nematode parasites tested, while the peptide hormone, insulin, stimulated growth in the protozoans tested. The evidence for in vitro effects of host hormones on their natural endoparasites is patchy at best. Additional studies are needed to identify the biochemical bases for the numerous host hormone mediated effects on parasites.

Morphometric study of Schistosoma mansoni adult worms recovered from undernourished infected mice

“…Various hormones of vertebrate hosts have been implicated in the stimulation or induction of growth or sexual reproduction of their parasites (Lawrence 1991). It is also known that in IL-7-deficient mice, S. mansoni female worms show an altered fecundity, leading to decreased numbers of eggs trapped in the tissues and to an amilioration of the pathology in the infected host.…”

Schistosoma mansoni (Platyhelminthes, Trematoda) nuclear receptors: Sixteen new members and a novel subfamily

“…Unlike other trematode parasites, Schistosoma species have evolved separate sexes and have a complex life cycle that involves mammalian and snail hosts. During the development of Schistosoma parasites within the vertebrate host, hormonal signals that seem to influence parasite migration, development, growth and sexual maturation are postulated to originate from the parasite itself and/or from the host (Beckage, 1991;de Mendonca et al, 2000a;Lawrence, 1991). Despite evidence that shows an influence of hormones on schistosome function, it is unknown which schistosome NR are involved.…”

Experimental manipulation of tail ornament size affects the hematocrit of male barn swallows ( Hirundo rustica )

“…Male ornaments preferred by females may be costly to produce because of the anabolic energy demands for their development or otherwise negative effects of hormones which ultimately control their growth (Beckage 1983;Grossman 1985;Lawrence 1991;Folstad and Karter 1992). Larger ornaments may also impose higher costs for their maintenance than smaller ones.…”