Microbiology - Parasites - Helminths

Parasites - Helminths Range in size from microscopic to 20m long. Each worm has both male and female organs. Two types: flatworms ( platyhelminthes ) and roundworms ( nematoda ) Requires a host to complete its life cycle. Adults usually live in intestines and shed eggs or segments. Intervertebrates: any animal without a spinal column. They are classified into over 30 phyla. Reproduction depends on the species of worm. If a male and female worm join, they produce eggs. When segments break off, the segments will contain both male and female sex organs, to produce eggs. Life cycle of intestinal parasites: The infected individual will contaminate soil with faeces containing the helminth’s eggs. These eggs develop, and then are ingested by other individuals through food, via dirty hands, or by larvae penetrating the skin. Parasitic worms will disrupt nutrient absorption, causing weakness and disease. Platyhelminthes: flattened worms covered by a tegument acoelomate: has no body cavity which separates its body from its digestive tract the excretion system is ciliated cells which extend into excretory tubules most are hermaphroditic, except schistosomes. Adult worms will produce sexually, and larvae (immature worms) will reproduce asexually. TYPES: Tremoda (Flukes) These attach to host tissue using suckers. They are leaf-shaped. 2. Cestoda (Tapeworms) No digestive cavity. Humans are the primary host; cows, pigs and fish are the intermediate hosts. They are elongated, have segments called proglottids, and have scolex (heads). TAENIASIS - a parasitic infection caused by 3 different species of tapeworms. You become infected by eating raw or undercooked beef or pork. Symptoms are usually mild or non-existent. CYSTICERCOSIS - tissue infection caused by Taenia solium tapeworm. Solid lumps may develop under the skin. Can affect the heart, muscle, and brain, and neurocysticercosis affects the brain and causes neurological symptoms and seizures. Nematodes: round and bilaterally symmetrical sized between 1mm and 1m. has organs and a complete digestive system. separate sexes has moulting stages - shedding has an acellular cuticle and a subcutaneous layer of muscle. bowel nematodes reside in the bowels as mature worms, eg Trichuris trichiura (whipworm) causes Trichuriasis which is common in tropical countries. A stool sample will show whipworm eggs which are barrel-shaped. People will defecate outside in soil, and this soil will be untreated and used as fertiliser. With a few worms, there are no symptoms; with many worms, there is abdominal pain, tiredness and diarrhoea which sometimes contains blood. This can also cause anaemia due to blood loss. Hookworms: Eggs in faeces hatch and mature as larvae in soil. Larvae will penetrate host skin eg through bare feet. Circulates to lungs Attaches by mouth to small intestinal mucosa, and sucks blood. Takes 4-5 weeks to penetrate skin and to produce eggs. Lives for 5-15 years as an adult. Enterobius vermicularis one of the most common nematode infections. Humans are its only host Lives in the ileum and cecum Faecal-oral infection can occur via contact with contaminated clothes, bedding, hygiene products and furniture. Testing: cellophane tape test or pinworm paddle test. Strongyloides stercoralis - Strongyloidiasis Threadworm Presents as GI symptoms but is asymptomatic in over 60% of cases. Difficult to diagnose, and can persist for decades. Risk of developing strongyloides hyperinfection syndrome, a life-threatening complication of systemic sepsis and multi-organ failure. Ascaris lumbricoides - Ascariasis Directly transferred from humans by skin contact, through contaminated vegetables where the soil has had faecal matter deposited, contaminated water, and contact with pets which have touched contaminated soil. Transmission also through municipal recycling of wastewater into crop fields, contaminating vegetables. PREVENTION: frequent hand washing frequent cleaning of bathrooms and kitchens thorough cooking of foods chlorinated water supplies DIAGNOSIS: medical history physical exam lab analysis of stools TREATMENT: - anti-worm drugs (vermifuges) which kill worms