Eukaryotes 5 - Animalia Fall 20 PDF

Helminths  Kingdom: Animalia All Heterotrophic, Multicellular (no cell walls) Helminths —microscopic parasitic worms – Many are highly adapted to a parasitic lifestyle Specialized and modified structures allow survival in animal host Some obligate parasites,...

Helminths  Kingdom: Animalia All Heterotrophic, Multicellular (no cell walls) Helminths —microscopic parasitic worms – Many are highly adapted to a parasitic lifestyle Specialized and modified structures allow survival in animal host Some obligate parasites, others facultative Estimated 3.8 billion infections currently worldwide Host Parasite Relationships – Definitive (final) vs. Intermediate hosts If 2 hosts are required to complete the lifecycle And the stage is Host Specific: Fertilization in one and growth and maturation in another – Only adults can reproduce – Classification based on morphology Flat or round in cross-section  Infestation vs. Infection Infection – Defined as multiplication in tissue, increase in population size of microbe Example: bacteria multiply, yeast, protozoa multiply and become millions in population size Infestation – Defined as invasion, but numbers do not increase by means of reproduction Numbers increase if more invade – Example: 2 worms produce 20,000 eggs. Eggs leave your body. You still have just 2 worms. You are infested, not infected. – Only way to get 3rd or 4th worm, same way you got first 2 (ingest eggs or larvae, vector transmission, direct penetration)  Classification Phylum: Platyhelminthes (flat worms) – Flattened in cross section Tapeworms and Flukes in different classes Phylum: Nematoda (roundworms) – Round in cross section Various genera – Ascaris and Enterobius (infective eggs, oral-fecal route) – Trichinella (infective larvae, ingestion) – Wuchereria (filarial roundworms, infective larvae, vectored)  Tapeworms Highly adapted to parasitism Specialized structures – Scolex for attachment – Hermaphroditic (bio term is monoecious) Taenia sp. Proglottids (sex organs in each, many eggs produce) – No digestive system, minimal musculature, movement Taeniasis – tapeworm infestation Ridiculous: uninformed and dangerous* Humans are part of the tapeworm lifecycle, BUT… Eggs are ‘supposed to be’ taken up by the intermediate host (hatch, develop in cow) Then mature to adults in our body, the definitive host. When eggs are in wrong host, larvae get lost, may migrate and develop in our brain. *still considered a weight-loss option!  Taeniasis vs. Cysticercosis Humans are the definitive host for Taenia solium (pig tapeworm) and T. saginata (beef tapeworm) – Eggs or gravid proglottids passed with human feces – Pigs and cattle ingest contaminated vegetation – Eggs hatch and migrate to striated (skeletal) muscle – Human ingests larvae in undercooked meat Worm attaches to small intestine by scolex Up to 2000 proglottids, 100,000 eggs in each! Correct route Eggs pass out Incorrect route T. solium eggs can lead to cysticercosis – Human ingests eggs, larval cysts infect brain, muscle, or other tissue, and are a major cause of adult onset seizures in most low-income countries.  Schistosomiasis Schistosoma (blood fluke) 1. Eggs released into irrigated fields Miracidia -ciliated larvae 2. Ciliated larvae invade snails 3. Multiplies and transforms into fork-tailed larvae 4. Released from snails 5. Enter human via skin, mature, mate, and lodge in small blood vessels, feed on blood 6. Eggs voided in feces (or urine) Cercaria -tailed larvae Symptoms of chronic schistosomiasis include: abdominal pain enlarged liver blood in the stool or blood in the urine problems passing urine Copulating flukes pair increased risk of bladder cancer and remain permanently entwined (kinda romantic) Figure 23.28 Schistosomiasis. 1 Adult female 8 Cercariae travel through circulatory flukes lay system to intestinal eggs. Male blood vessels, Definitive where they mature Female Mouth host (size: into adults. Adult Sucker 15–20 mm) flukes Eggs Female Mouth Male 7 Free-swimming (a) Male and female cercariae penetrate schistosomes. The Cercaria female lives in a groove human skin, (0.13 mm) 2 Eggs reach losing tail. body of on the ventral (lower) water after surface of the male being excreted schistosome in human (“split-body”), is feces or continuously fertilized, urine. and continuously lays Egg eggs. The sucker is used Cercaria (0.33 mm) (0.15 mm) by the male to attach to the host. Intermediate 3 Eggs hatch into free-swimming host larvae (miracidia). 6 Cercariae are released from the snail. 5 Miracidium reproduces Miracidium 4 Miracidium (0.2 mm) in snail, forming (b) Life cycle of Schistosoma, several cercariae. penetrates snail. cause of schistosomiasis.  Roundworms Prolific reproductive capacity – Some produce 200,000 eggs per day Cuticle (outer layer) provides protection against harsh environments (digestive tract) Intestinal and Tissue parasites  Soil-Transmitted Helminths Ascaris and hookworms are acquired through contact with soil contaminated with infected feces. – More than four billion people are at high risk throughout the world, with over one billion individuals already infected. – STH infections can contribute to anemia, vitamin A deficiency, malnutrition and impaired growth, delayed development, and intestinal blockages. Hookworms cannot be acquired directly, require period free living in soil – Fewer cases in US due to indoor plumbing and wearing of shoes! Ancylostoma and Necator Large Intestinal Roundworms Ascariasis is the most common human worm infestation Ascaris lumbricoides Eggs ingested (remember Eggs nightsoil), hatch in intestine – Burrow OUT of intestine to be picked up by circulatory system – Reach lungs, migrate upward to throat to be swallowed – Larvae return to intestine to mature Abdominal pain, diarrhea Intestinal obstruction and blockage of ducts (worms remain motile)  Pinworms (seat worms) Common intestinal parasite of children – Most common type in US – Human only host – Fecal-oral route Enterobius vermicularis Eggs ingested, – hatch in Small Intestine – mature in Large Intestine – adults mate Female exits GI tract to lay eggs, then re-enters – Irritation contaminates hands – Hand to mouth transmission – Dried eggs become airborne  Trichinosis (zoonosis) Trichinella spiralis Eggs ingested by swine (or other carnivore/omnivore) – Digestive acids cause excystment, worms mature and mate – Eggs hatch, larvae migrate to skeletal muscles and encyst – May survive for years Undercooked (or raw) meat eaten by new host (human) Cycle not completed when worm encysts in human tissue (accidental parasitism), no one eats us to release parasite. Figure 25.26 The life cycle of Trichinella spiralis, the causative agent of trichinellosis. Ingested cysts develop into Trichinella spiralis adults in Adult worms produce larvae that the pig’s intestinal wall. encyst in the pig’s muscles. Garbage, including undercooked or raw pork Capsule Section of encysted Meanwhile, T. spiralis other animals eat infected meat that has been dumped. Human eats undercooked pork containing cysts that are infective to humans or animals that ingest it. Trichinellosis in humans; ingested cysts develop into T. spiralis adults. Adults produce larvae that encyst in T. spiralis adult muscles.  Filarial Roundworms Lymphatic filariasis (elephantiasis) – Chronic deforming disease – Increases risk of bacterial infections Wuchereria bancrofti – Mosquito picks up ‘microfilariae’ from diseased host – parasites develop into infective larvae and migrates to vector’s mouthpart, passed to next host during blood meal – worm matures in vessels and reproduces, more microfilariae produced – Blockage of lymphatics causes edema of lower extremities, hydrocele in men (swelling of the scrotum)  Additional info Bite deposits and/or picks up juveniles (larvae) in skin – (parasites swarm to skin of infected host during times mosquitoes feed) Long-lived worms develop in lymphatic vessels, release huge numbers of offspring – Infection in the young is subclinical – Many infected will never develop symptoms – 1 to 5 decades of chronic infection before massive swelling results from blockage  Other important roundworm parasites Guinea Worms – Ingestion of copepods in water ‘water fleas’ carry larvae Eye Worm (Loa Loa) – Biting black fly vector Heartworms (canine filariasis) – Mosquito vector Onchocerca (River Blindness) – Black fly vector (truly heart breaking cycle of misery)  Last thoughts on Parasites… Parasites REQUIRE a host to feed and reproduce – Parasitism MUST involve provision to leave host and success depends on an encounter with next host. Millions of people suffer and die from preventable and curable (not all) diseases. – What can be done to help? Preventing is more important that curing, but access to a cure would be progress  Human Impact (infections) (deaths per year) All helminths 4.46 billion Ascaris 1221 million 60,000 Hookworms 740 million 65,000 Filarial worms 657 million 20-50,000 Schistosomes 200 million 20 million Malaria 298-659 million 1-2 million Entameoba 50 million 40,000 – $543+ per case for cancer (NCI) – $32+ per case for cardiovascular disease (MHL&BI) – $0.004(+?) per case for schistosomiasis (WHO) Consider the ‘parasitologist’s dilemma’ and ways in which ‘misery compounds itself’. (more people survive disease, more people to starve)  Neglected Parasitic Infections in US A group of five parasitic diseases that have been targeted by CDC as priorities for public health action. Selection based on: – Number of people infected – Severity of the illnesses – Ability to prevent and treat them List includes: – Chagas Disease – Cysticercosis Note: red font represents helminthes – Toxocariasis Boldface font represents protozoan – Toxoplasmosis diseases we will look at here – Trichomoniasis These infections are considered neglected because relatively little attention has been devoted to their surveillance, prevention, and/or treatment. Anyone, regardless of race or economic status, can become infected although minorities, immigrants, and people living in poor or disadvantaged communities appear to be most at risk.  Neglected Tropical Diseases Neglected Tropical Diseases (NTDs) are a group of parasitic and bacterial diseases that cause substantial illness for more than one billion people globally. Affecting the world's poorest people, NTDs impair physical and cognitive development, contribute to mother and child illness and death, make it difficult to farm or earn a living, and limit productivity in the workplace. As a result, NTDs trap the poor in a cycle of poverty and disease. Chagas disease Cysticercosis Dracunculiasis (Guinea Worm Disease) Human African Trypanosomiasis (African Sleeping Sickness) Leishmaniasis Lymphatic filariasis Onchocerciasis Schistosomiasis Soil-transmitted Helminths (STH) (Ascaris, hookworm, and whipworm)  Arthropods as Vectors Can transmit disease (vectors) Kingdom: Animalia – Phylum: Arthropoda (exoskeleton, jointed legs) Class: Insecta (6 legs) – Lice, fleas, mosquitoes Class: Arachnida (8 legs) – Mites and ticks