6 The helminths Flashcards
Helminth term used for groups of parasitic worms.
What are names of:
Tapeworms
Roundworms
Flukes
More common in tropical climates, as favours survivial of infective stages, and poor socio-economic conditions which facilitate faecal-oral transmission, and poor food preparation
Tapeworms - cestodes
Roundworms - nematodes
Flukes - trematodes
Cestodes/ tremadoes - phylum flatworms. Flat bodies, muscular suckers, and hooks for attachments.
Roundworms - phylum roundworm. Long cylindrical bodies and lack specialised attachment organs
What are transmission routes of helminths
Most helminths (except strongyloides) do not replicate in host. Mostly, sexual reproduction in intestines results in production of eggs, which are released in faeces
Swallowing infective eggs or larvae - faecal-oral
Swallowing infective larvae in tissue of other host e.g pork
Active penetration via skin - e.g schistosomiasis
Injection by blood-sucking vector e.g filariasis
How do helminths get nutrition
Outer surfaces of helminths (tapeworms/ flukes) have complex plasma membrane, which protects to prevent host damaging it, as resistant to immune attack. Smaller larval stages may be attacked by immune system. Worms release large amounts of soluble antigenic material , which directs immune system towards. Schistosomiasis for exmaple, inserts host antigens into surface, to help evade destruction by macrophages/ T cells. Many worms become too big to be damaged by cells/ antibodies
Flukes/ roundworms can feed on host tissues or intestinal contents
Tapeworms feed on pre-digested food
What are direct and indirect life cycles of helminths
Direct - reproductive stages produced by sexually mature adults in one host, are released from body, and infect other host e.g ascaris, hookworm
Indirect - requires intermediate host (pork tapeworm) or vector (filarial worms) before sexual maturity can be achieved in final host
Most flukes are hermaphrodites (except schistosomes).
Nematodes (round worms) can develop to maturity within single host.
How to nematodes replicate?
Sexes are separate, and produces fertilised eggs.
Adult tapeworms are acquired by eating undercooked or raw meat containing larval stages (or eggs). all develop in GI tract
What are species names of adult tapeworms acquired from these sources:
- larvae in beef
- larvae in in pork
- larvae in fish/ fish-eating mammals
- larvae in beetles/ rodents
- larvae in beef - taenia saginata
- larvae in in pork - taenia solium (cysticercosis). Can also acquire eggs in food/ water
- larvae in fish - diphyllobothrium latum
- larvae in beetles - hymenolepsis nana
What are species names of tapeworms acquired from these sources:
- eggs in dogs/ sheep/ rodents
- Echinococcus granulosus (cystic echinococcois). Infects liver, lungs, brain
- Echinococcus multilocularis (alveolar echinococcus) . Infects liver
Most important flukes are those causing schistosomiasis.
What are the main species
S. haematobium - blood vessel of bladder
S. Mansoni - blood vessels intestine
S. japonicum - blood vessels intestine
Apart from schistosomiasis, what are other human fluke infections, and how are they acquired
Clonorchis sinesis - oriental liver fluke. Ingesting fish infected larval stages
Opisthorchis viverrini - bile duct. Ingesting fish infected
Fasciola hepatica - sheep liver fluke. Ingesting vegetation (watercress) infected larval stages
Paragonimus westermani - lung fluke. Ingesting freshwater crabs infected with larval stages
Which nematodes infected GI tract?
ingestion of eggs/ skin penetration by larvae
Ascaris lumbricoides. Ingestion of eggs.
Enterobius vermicularis. Ingestion of eggs.
Hookworm (ancylostoma duodenale/ necator americanus). Skin penetration by infective larvae
Strongyloides stercoralis - skin penetration infective larvae.
Trichuris trichiura. Ingestion of eggs.
Which nematodes are transmitted person to person via arthropod carrying infective larvae?
Brugia malayi - mosquito. Lymphatics (adults). Blood (larvae)
Onchocerca volvulus - simulium fly. Skin (larvae/ adults). Eye (larvae)
Wuchereria bancrofti - mosquito. Lymphatics (adults). Blood (larvae)
Loa loa - deer fly. Subcutaenous tissues called calabar swellings (adults). Blood (larvae)
Humans can also be infected with larvae of nematode species that mature in other animals.
What are examples?
Toxocara canis - dog host, eggs passed in stool. Tissues, eyes, CNS
Trichinella spiralis - pork host. Small intestine (adults), muscles (larvae)
Larvae of tapeworms/ flukes must pass through intermediate host.
How do tapeworms reproduce?
Tapeworm reporductive organs are replicated along the body (the stobila) in series of proglottids. Terminal proglottid becomes filled with mature eggs, detach, and pass out in faeces
Classification of nematodes is complex. How are they classified?
Classification of nematodes is complex. For human purposes :
- those which mature in GI tract, some may migrate through body during development - ascaris, hookworm, trichinella, strongyloides, trichuris
- those which develop in deeper tissues e.g filaria
What are examples of nematodes which infect humans?
Intestinal
Anisakiasis Ascaris Enterobius Hookworm - necator/ ancylostoma Strongyloides Trichuris
