HELMINTHES

Characteristics:Traditionally classified in Kingdom Animalia, now in Domain Eucarya Super Group Opisthokonta

•Eucaryotic•Multicellular•Chemoorganotrophic

• Worms may be "free living" or "parasitic”

Obligate parasites - they cannot complete their lifecycle without a host(s)

Facultative - they may be parasitic but can also survive as free-living

Considered as endoparasites or ectoparasites

Factors in parasitology:

• do not usually kill their host • evolve elaborate cycles of reproduction• high rate of reproduction• complex life cycles involving 1 or more hosts

- usually host specific• development of specialized structures (hooks,

suckers, etc.)• ability to fight immune system (production of

enzymes, changing antigens, other disguises)• loss of structures (eyes, locomotion, etc.)

Classification – Super Group Opisthokonta:

• Phylum Platyhelminthes – “Flat Worms”• most primitive• dorsoventrally flat• nonsegmented• acoelomic - no body cavity• incomplete digestive tract• free-living and parasitic• hermaphroditic except blood flukes• sexual and asexual reproduction• ability to regenerate

Class Trematoda- "Flukes"

• From lab - Fasciola hepatica, Clonorchis sinenesis, Schistosoma

• oral and ventral suckers which function to attach and aid in locomotion

• surrounded by integument whose surface contains spines and projections

• all flukes are parasitic as adults • utilize snails as their first intermediate host• produce operculated eggs which are eggs

that have an operculum, or lid

Specific stages as larvae:

• miracidium

• sporocyst

• redia

• cercaria

• metacercaria

• Lifecycle of the blood flukes - Schistosoma japonicum, S. mansoni, S. haematobium, S. intercalatum, S. mekongi

Lifecycle of liver fluke - Clonorchis sinensis

Class Cestoda - "Tapeworms"

• From lab - Taenia, Dipylidium• all are parasitic - endoparasites, usually in the

digestive tract• have an attachment organ - scolex which has

hooks on a rostellum and suckers• next is a neck followed by “segments,” or

sections called proglottids containing reproductive organs which become more mature towards the end of the worm

• the "body" is referred to as a strobila

• produce operculated ova like the flukes• feed by absorbing nutrients through the body

wall• an adult cestode can range from 0.02 to 10

meters• different species of tapeworms infect different

hosts, many are host specific and will not infect other org outside the host, others will

• Lifecycle of Taenia soliumincluding cysticercosis

Phylum Nematoda - “Unsegmented Roundworms”

• From lab - Wuchereria bancrofti, Trichinella spiralis, Enterobius vermicularis, Ascaris lumbricoides, Necator americanus

• unsegmented, cylindrical, long and slender• complete digestive system• pseudocoelomic: false body cavity - not lined

with tissue derived from mesoderm• separate sexes• body is covered by a cuticle with ridges,

striations or wart-like structures

• Lifecycle of Enterobius vermicularis

• Lifecycle of Ascaris lumbricoides

• Lifecycle of Necator americanus

Lifecycle of Trichinella spiralis