Introduction to Nematodes PDF

Lecture Objectives Nematodes – Know the key characteristics – Be able to determine if a life cycle is direct or indirect – Be able to identify the types of hosts in a life cycle – Be able to identify methods nematodes use to ensure the survival of their species – Understand the impact of grazing on...

Lecture Objectives Nematodes – Know the key characteristics – Be able to determine if a life cycle is direct or indirect – Be able to identify the types of hosts in a life cycle – Be able to identify methods nematodes use to ensure the survival of their species – Understand the impact of grazing on nematode infections – Be able to describe the balance between pasture nutrition and parasite management Lecture Objectives Ancylostoma caninum – Know the primary clinical signs – Know the primary modes of infection – Be able to relate morphology & behaviour to pathology and clinical signs Parasites of veterinary importance Phylum Nematoda (Roundworms) Phylum Platyhelminthes (Flatworms) – Class Cestoda (Tapeworms) – Class Trematoda (Flukes) Helminth = worm Live extracellularly: in the gastro-intestinal tract and organs Helminths Sexual reproduction – Nematodes: Males and females – Cestodes & trematodes: hermaphroditic – Egg-laying (oviparous); some lay live young (viviparous) Do not multiply within the host – Offspring must leave host – Some cestode larval stages an exception Increased infection results from increased environmental exposure Nematodes (roundworms) Free-living or parasitic – Soil and plant nematodes – Animal nematodes Elongate/cylindrical Alimentary canal present Sexes usually separate – Egg-laying (oviparous); some lay live young (viviparous) – Do not multiply within the host – Offspring must leave host Increased infection results from increased environmental exposure Life cycle direct or indirect Helminths Courtesy Elanco Nematodes (roundworms) Alimentary canal present Photo: J. Ketzis Nematodes (roundworms) Alimentary canal present Sexes usually separate Nematodes (roundworms) Bursate (male) or not Vulva Mouth (shape, teeth) Esophagus Size Aids in identification Lecture Objectives Nematodes – Key characteristics – Life cycles – Hosts – Means of species survival Ancylostoma caninum Nematodes – life cycle E – (mff) L1 - L2 - L3 - L4 - L5 - Adult – Pre-L1 = microfilaria (some nematodes) mff – L5 = immature adult Insert host(s) – Final or definitive – Intermediate – Vectors, paratenic, etc. Insert mode of infection (per os, percutaneous, transmammary, transplacental Nematodes – life cycle Life cycle Direct – infective larva (usually L3) – infective larva in an egg (usually NOT L1) Indirect – L1 infective to intermediate host – L3 to the final host Nematodes – life cycle In feces In feces L1-L2-L3 Host L3 In grass L3 L3-L4-L5-Adult-eggs Nematodes – life cycle In feces In feces In grass L1 L1-L2-L3 L3 Host L3-L4-L5-Adulteggs-L1 in egg-L1 Nematodes – life cycle Insert means of survival How they ensure offspring get in a host – – – – Survival of eggs with larva Paratenic hosts Transmammary, transplacental Periparturient rise Avoid immune system/crowding/“badweather”: – Arrested development/Hypobiosis/Inhibited development Nematodes – life cycles Courtesy Elanco Nematodes – life cycles Courtesy Elanco Nematodes – life cycles Novartis Animal Health Nematodes – life cycles Some can survive on pasture in winter Some have to find another means of making the pasture infected – arrest and emerge in spring; periparturient rise Life cycles Trichostrongyle fecal egg counts; ACSRPC 34 Nematodes – life cycles ‘immune exclusion’ or rapid larval rejection L3s gone in 48 h Hypersensitized sheep; previous exposure IgE, increased peristalsis of the gut Delayed rejection L3s enter mucosa and eventually die Naive sheep Eosinophil-mediated larval killing (antibodydependent cell cytotoxicity) 35 Nematodes – life cycles L3 exsheaths and now L4 Crowding; adult excretion = arrests Older L3 = slower development = inhibited Immune protection = arrests Immune protection = regulates feeding Small L4 Small adult Fewer eggs 36 Nematodes – life cycles Spring time! L4 resume development after a few months (regardless that it is spring) Spring rise in egg count, periparturient rise New L3 cause “self-cure” or premonition Hypobiosis as a winter strategy is a potential misconception Alternate theory Ewes lose immunity around lambing (-2 - +8 wk) Results in higher infection 37 Nematodes – life cycles Epidemiology – when exposure occurs – when heavy infections occur – when there is the most pathology & clinical signs – how to intervene Usefulness of fecal egg counts Take home message: if you know how the species perpetuates, you can know how AND WHEN to intervene! Nematodes – life cycle E - L1 - L2 - L3 - L4 - L5 - Adult – L1 = mff; L5 = immature adult Insert host(s) – Final or definitive – Intermediate – Vectors, paratenic, etc. Insert mode of infection (per os, percutaneous, transmammary, transplacental Insert means of survival Nematodes – Pastures Animals on pasture in spring Animals in barn in winter Pasture rotations to maximize nutrition Often 30 days – depends on weather, stocking rate, time of year, type of pasture Nematodes – Pastures Eggs to L3: a few days to a few weeks L3 life span a few weeks to 3+ months L3 accumulate Day 1: 100 eggs; Day 2: 100 eggs; Day 3: 100 eggs, etc. Day 7: 100 L3, Day 8: 200 L3; Day 9: 300 L3, etc. On pasture for 30 days: all the L3 from eggs deposited in previous 23 days and, in 7 more days, all L3 from all 30 days Lecture Objectives Ancylostoma caninum – Know the primary clinical signs – Know the primary modes of infection – Be able to relate morphology & behaviour to pathology and clinical signs Ancylostoma caninum Round; elongated; males and females Buccal cavity – teeth Size – 1-2 cm Bursa -- yes Host – caninum = dogs Mode of infection – many modes Prediliction site – adults small intestines; larvae migrate in lungs Food – adults blood Life cycle -- direct Nematodes – Ancylostomatoidea Adults: small (1-2 cm); characteristic hook appearance; bursa; small intestine Attach to the intestinal villi with large mouth (buccal) cavity Caryn Ehrhardt (males; stained) Thomas Nolan Ancylostoma caninum PPP: 2-3 wk Paratenic hosts Elanco Ancylostoma caninum Life cycle: Direct Five modes of infection – Percutaneous or penetration of oral mucosa – Per os – Paratenic hosts (e.g., rodents) – Transplacental (rare) – Transmammary (important) Arrested development Lung migration Ancylostoma caninum Pathogenesis and lesions Acute or chronic hemorrhagic anemia Moist eczema with percutaneous infection Acute infections clinical signs Anemia and lassitude Respiratory disease (larval migration); pneumonia Diarrhea (blood and mucus) Chronic infections clinical signs Weight loss, poor hair coat etc.) Nematodes – Ancylostomatoidea Hemorrhaging Anemia Photo courtesy of Dr. Thomas Nolan Nematodes – Ancylostomatoidea Eggs: oval, thin shelled; 60 X 40 µm Photo: Zajac and Conboy, 2012 Ancylostoma caninum Diagnosis: Clinical signs Fecal examinations A few hookworm eggs confirms infection (-iasis) only, not hookworm disease L4 / early mature also feed on blood Nematodes – Ancylostomatoidea Summary Hookworms Adults: 1-2 cm; small intestine Buccal capsule modifications: teeth, cutting plates Anemia: feed on blood; ulcers Pneumonia: larval migration Eggs: oval, thin shelled, 60 x 40 µm Young animals most severe signs Limited immunity Zoonotic (cutaneous larval migration) Impact of parasites Blood feeding Hoste et al. 2016. Interactions between nutrition and infections with Haemonchus contortus and related gastrointestinal nematodes in small ruminants. Advances in Parasitol 58