Veterinary Helminthology: An Overview

• Theme 3.1 concerns helminths and their importance in veterinary and agricultural contexts.

Introduction and Terminology

• Parasitology studies the phenomenon of parasitism.
• Veterinary and medical parasitology focuses on protozoa, arthropods, and helminths of veterinary and medical importance.
• Protozoology, ectoparasitology (entomology), and helminthology, are sub-disciplines

Parasitism

• Parasitism involves interrelationships between different species - biological phenomenon.
• A parasite is a eukaryotic organism.
• It lives temporarily or permanently on/in a host organism of a different species at the host's expense.
• It has pathogenic properties.
• Parasitosis/parasitoses are infections, infestations, and diseases caused by parasites.
• Veterinary parasitology uses Standardized Nomenclature of Animal Parasitic Diseases (SNOAPAD), while medical parasitology does not

Nomenclature, Taxonomy, and Systematics

• Nomenclature names organisms based on the International Code of Zoological Nomenclature (ICZN).
• Taxonomy allocates organisms to a taxon based on morphological, biological, genetic, and other criteria.
• A taxon is a classificatory group or unit in the biological system, such as species, genus, family, and kingdom.
• Systematics describes, delineates, and arranges taxa in a hierarchical system to reflect the phylogeny (evolutionary pathway)

Veterinary and Medical Parasites

• Veterinary and medical groups are relevant as eukaryotic organisms (protozoa, metazoa) that cause disease and vectors

Nomenclature

• Binomial nomenclature scientifically names organisms with two parts.
• Genus is the first part, and species epithet is the second part, mostly Greek and Latin in origin.
• The epithet identifies a subordinate unit within a genus.
• Species names are usually italicized or underlined.
• Common names lack standardized or universal application.
• An example is Calicophoron microbothrium (scientific name) which is also known as rumen fluke or conical fluke (common names).

Categories of Parasites

• Parasites' categorizations are based on location, organ, dependence, contact duration, life cycle phase, and host specificity.
• Location can be ectoparasites or endoparasites.
• Host dependence can be either obligate, facultative, or opportunistic.
• Contact duration can be temporary or stationary.
• Parasitic phases in life cycle are permanent or periodic.
• Host specificity can be stenoxenous (narrow host spectrum) or euryxenous (broad host spectrum)

Categories of Hosts

• Hosts include definitive/final, intermediate, paratenic, accidental, and aberrant types.
• A definitive or final host is where the parasite matures and reproduces sexually.
• An intermediate host is where larval stages develop to become infective
• A paratenic host harbors infective larval stages without further development but remains infective for the definitive host.
• Accidental hosts permit parasite development but lack epidemiological significance.
• An aberrant host limits parasite development

Infection vs. Infestation:

• Infection is correctly used for endoparasites.
• Modes include ingestion, percutaneous, transplacental, transmammary, venereal, and iatrogenic routes.
• Infestation is correctly used for ectoparasites (arthropods)

Pathogenesis, Pathogenicity, and Virulence

• Pathogenesis is the formation/development of abnormal processes.
• Pathogenicity is the ability of an agent to cause disease, differing between host species.
• Virulence is the degree of pathogenicity.

Pathogenic Effects

• Effects are often subclinical, including cytopathogenicity, mechanical effects (destruction/blockage), inflammation, blood/substrate withdrawal, immunopathology, excretion of active substances, and pathogen transmission

Epidemiology

• Epidemiology studies factors influencing disease frequency and distribution.
• Reasons for parasitic diseases include increased infective stages, changed host susceptibility, and introduction of new animal species

Parasitic Zoonoses

• Zoonoses are diseases and infections/infestations naturally transmitted between vertebrate animals and humans

Classification of Helminths

• Parasitic helminths exist in two phyla: Platyhelminthes (flatworms) and Nematoda (roundworms)

Platyhelminthes

• Platyhelminthes have two classes; Class Trematoda (trematodes or flukes) and Class Cestoda (cestodes or tapeworms)
• Body is dorsoventrally flattened, hermaphroditic (with exceptions), and lack a body cavity
• They have a complete intestinal tract or no elementary canal (tapeworms) and undergo indirect life cycles

Nematoda

• Nematoda Orders are; Rhabditida, Strongylida, Ascaridida, Oxyurida, Spirurida, and Enoplida
• These worms have a cylindrical and unisexual body
• They have a body cavity and a complete alimentary tract (mouth, oesophagus, intestine, anus)
• Their life cycles can be direct or indirect.

Basic Life Cycle of Helminths

• Helminth development has three phases: embryonal, postembryonal, and definitive
• Embryonal development: Begins with ovum fertilisation resulting in the formation of a 1st larval stage
• Postembryonal development: 1st larval stage ends with infective larval stage formation.
• This happens exogenously (environment - direct life cycles) or endogenously (intermediate host - indirect life cycles0
• Definitive development: Begins with final host infection, ending at adult stages with sexual reproduction

Prepatent Period (PPP)

• (PPP) PPP is the time from infection to mature parasite egg/larvae production.

Patent Period (PP)

• (PP) PP is the timeframe after PPP when parasite sexual products can be found in material samples (faeces, blood, urine, saliva)

Postpatent Period

• Following patent period, the helminth infection continues, but sexual products are gone

Immunity to Helminths

• The immune system is inefficient in controlling helminthoses
• Morbidity is more relevant than mortality, since most worms do not replicate in their definitive hosts
• Large worm burdens or non-adapted parasites cause acute disease
• Worm burden depends on host genetics and response

Control of Helminth

• Helminth infection control aims to minimize parasitic subpopulation via free-living subpopulations, economic losses, and clinical disease onset

Rationale

• Rationale includes clinical cure, human infection/zoonosis risk minimization, ethical considerations, and owner satisfaction

Approaches

• Host management: includes monitoring, anthelmintics, breeding for resistance, appropriate nutrition, and vaccination.
• Habitat management: includes hygiene, faeces removal, sanitation, sewage treatment plants
• Other management: includes alternate/rotational grazing, farming/stocking density, and IH vector control

Anthelmintics

• Control uses anthelmintic drugs for prophylaxis, metaphylaxis, or curative treatment.

Antiparasitic Drug Resistance:

• Parasite populations showing decreased drug response are considered resistant.
• Susceptible strains are killed whereas resistant/drug-tolerant strains are not affected is observed in some cases.
• Contributing factors include high treatment frequency, single-drug regimens, long-acting drugs, mass treatments, and underdosing

Anthelmintic Resistance:

• Anthelmintic resistance is detected via faecal egg count reduction tests (FECRT) and laboratory tests

Tolerance

• Tolerance is the innate drug unresponsiveness towards a developmental stage or a parasite.

Resilience:

• Resilience is the ability to cope with infection effects without severe morbidity and mortality.

Trematoda

• Trematoda are the trematodes or flukes

Trematoda Classification

• Belong to the Phylum Plathelminthes, Class Trematoda, and Subclass Digenea
• Families of trematoda are the Fasciolidae and Blood flukes

Keynotes for Trematoda

• Digenetic trematodes widely parasitize fish, amphibians, reptiles, birds, and mammals
• Adults are in parts of the GIT, bile and pancreatic ducts, lungs, kidneys, urinary bladder, blood vessels and selected areas of the body
• Body is dorsoventrally flattened, pear-shaped, or cylindrical.
• There are 2 suckers (oral and ventral) for attachment to the host.
• The body is covered by an absorptive tegument that is often spiny
• There is no coelum or "body cavity"
• The digestive system ends blindly
• Mostly oviparous
• Hermaphrodite (except Schistosomatidae)
• Indirect life cycle with 1 or 2 intermediate hosts, mollusc being the first

Life Cycle of Trematoda

• Eggs are released in urine, sputum, or faeces, and are sensitive to desiccation
• Miracidium is the 1st larval stage that requires water to infect an intermediate host such as an amphibious snail
• Sporocyst develops in the snail for asexual production
• Redia also develops in the snail where asexual reproduction occurs
• Cercaria leaves the snail, and becomes motile in the water
• Cercaria in water is the infective stage for mammals to cause percutaneous infection or ingestion of water
• Metacercaria attaches to plants in water, walls of drinking water, or is free in water
• Metacercaria is the infective stage for mammals through percutaneous infection or ingestion of water

Egg characteristics

• Cercaria requires poor resistance to desiccation; survival for almost 1 year if high humidity prevails.
• Immature and adult flukes are present

Important Trematoda Species

• Fasciola hepatica: Causes liver disease, and causes parasitic disease in cattle, sheep, goats and humans
• Schistosoma spp : Blood fluke causing Schistosomiasis

Trematoda development

• Parasitic development begins with the preparasitic development to the miracidium in around 9-10 days
• The intermediate host undergoes miracidium to metacercaria in about 6-7 weeks
• Infection with 1 miracidium can produce greater than 600 metacercariae in the intermediate
• Regarding the definitive host, infection occurs with the ingestion of metacercariae, and excystment of metacercaria occurs with migration in the liver

Trematoda characteristics:

• Trematoda can easily be seen macroscopically
• F asciola hepatica is around 20-50 mm long , and 4–13 mm wide
• F gigantica is measured to be around 25-75 mm long, 3-11 mm wide
• Flukes have a dorsoventrally flattened body shape
• Colour of flukes is brown-greyish
• They have conical anterior end
• Fasciola eggs are large and oval, are sized at F. hepatica 130-150 x 63-90 µm and F. gigantica 156-197 x 90-104 μm and contain fine granular material.
• They also are yellowish-brown, thin-shelled, and have an Indistinct shell
• Metacercariae is around Circular, 310-350 µm in Ø which are attached to plants or on the surface
• Trematoda is directly daignosable with egg detection in fecal samples

Epidemiology and Importance of Trematoda

• Development relies on permanent or semi-permanent water bodies
• Domestic ruminants act as reservoir hosts and Metacercariae are more resistant to desiccation
• Metacercariae can survive for commonly 4-6 months (up to 1 year)

Public health concerns:

• Metacarcariae can survive on vegetables grown in snail-infested habitats grazed by ruminants, on wild watercress, (3) floating in water, causing health concerns

Schistosoma

• Schistosoma is a genus of trematodes that belong to the class Trematoda, and cause schistosomiasis

Epidemiology of Schistosomiasis

• Schistosoma relies on aquatic fresh water snails for completion of their lifecycle

Types of Schistosoma

• Species of the Schisostoma are Schistosoma mansoni, Schistosoma haematobium, and Schistosoma mattheei, each with different animal targets

Life cycle of Schistosoma

• Cercariae is the infective stage of Schistosoma and they penetrate the dermis of mammals
• During penetration, cercariae loses its tail and transforms into schistosomulae which enters the circulatory system to the heart
• In the heart, schistosomulae are transferred to the liver for maturity, and enter the mesentric and/or bladder veins
• In the veins the schistosomulae mate, where the female is carried alongside the male
• Eggs are then hatched which can become lodged in blood and shed in feces from the mesentric veins, and urine from the bladder veins

Characters of Schistosomiasis

• The infective stage is the cercariae.
• The Schistosoma adults are elongated, unisexual, and measure 7-28 mm long with cylindrical, black bodies for females, and measure 6-22 mm long, 1-2 mm wide with longitudinally curved (gynaecophoric canal), white bodies for males
• Males carry females for reproduction

Schistosome Characteristics

• Schistosoma eggs are Oval and Large sized (112-175 x 45-70 µm), spindle shaped (83-187 x 60 μm, 170-280 x 72-84 µm) with a lateral or terminal spine.
• Diagnoses include examining fecal and rectal samples and urine filtration. The Schistosoma can be diagnosed using various methods of sedimentation and concentration on feces and blood samples,

Schistosoma Epidemiology

• Main source of infection is humans,
• Schistosoma is contracted by freshwater snails, therefore, it thrives in hot and humid temperatures
• Schistosome importance: chronic conditions can cause health problem
• Poor sanitation can intensify the cycle of disease that affects deprived communities

Cestoda (Cestodes, Tapeworms):

Classification:

• Belong to the Phylum: Plathelminthes
• Class: Cestoda
• Subclass: Eucestoda
• Families of them are Dipylidiidae, Taeniidae, Echinococcus

Keynotes

• Parasites mostly infect fish, amphibians, reptiles, birds, and mammals
• Diagnostic Feature: hermaphrodite
• Morphology:*
• Flattened dorsoventrally
• Several metres long
• Scolex+Suckers + Rostellum + Neck(growth region),
• Chain of segments termed Strobila
• Motile for excretion through defacation
• Features:*
  • No alimentary tract, Tegument, and Indirect Life Cycle with 1 IH
  • Sexual reproduction + High biotic potential
  • Larval stages in IHs with asexual reproduction in some species

Life Cycle:

• Eggs released free in gravid proglottids during defecation
• Eggs are embryonated (oncosphere = 1st larval stage in cestode life cycles) and immediately infective for IHs for ingestion
• Larval stage that develops in IHs (Metacestode) for ingestion
• Invertebrate IHs (Cysticercoid), and
• mammalsIHs (Cysticercus (measle) with Hydatid (hydatid cyst)

Dipylidiidae Keynotes:

• Dog/Cat and other carnivores are definitive hosts
• Invertebrates carries cysticercoids
• Dipylidium caninum
• Cosmopolitan

Definitive Hosts

:Dog + Cat + Man

Intermediate Hosts

:Fleas + Lice

• Life Cycle:*

  • Flea ingests eggs
  • Vertebrate host consumes infected flea

• Parasitic Development*

• Larval stages

• infective cysticercoids develop within 2-3 weeks in IH (flea or lice)

• DH is infected by the the ingestion of infected fleas/lice

• Characteristics:*

• 3 cm long

• "Cucumber seed:" are Longer than wide +Often with a reddish tinge

• Uterus (large): breaks up into egg capsules, 2-38 spherical eggs with striated embryophore

• Diagnosis: Motile gravid proglottids in feces

Epidemiology

IH are present and re-infection is an issue.

• Importance:
• Most common tapeworm for dogs and cats
• Largely non-pathogenic anal pruritus

Taeniidae ('Taeniids'): Keynotes

• Genus: Taenia and Echinococcuis.
• DH: Carnivores and Humans,
• IH: Mammals, and Cestode family with greatests relevance in public health
• Man:*
• Acting as DH: Infection with ingesting IH
• Acting as IH: Infection with ingesting infected eggs of adult worms occurring mostly in dogs
• strobilar stage The strobilar and segments
• Scolex with armed rostellum except T. saginata with proglottids that are longer than wide
• Metacestodes: Cysticercus + Hydatid _ Taeniid eggs_
• Cannot morphologically/ morphometrically differentiate between species

Life Cycle

• Direct cysticercoids

Key Species

• Taenia soilum
• Taenia saginata
• • DH**:Man
• Taenia hydatigen,
• Taenia multiceps Df= Dog

Intermediate Host

T. solium: pork musculature with CNS tissue

Taenia saginata: beef: muscle tissue

Distribution Cosmopolitan

. Life stages with cycle:

Echinococcus are developing cysticerci in muscle through ingestion of raw meat from a DH Ascaridida

• Infected with vegetation with infective stage from a definitive host

Diagnostics

Direct Eggs and specimens only

DH: Taenia

• Demonstrations in the feces

Taeniasis:

• Under cooked pork meat
• Public Health issues/concerns for taeniasis:

Risk of contraction

Ascaridida features

• Direct
• Direct lives and undercooked meat

Key Notes

• The class Nematoda for vertebrates
• Causative agents of infections to DH is Important
• In digestive / respiration and other
• Infections can be both Direct and Indirect

Nematoda and stages:

• Infective - 3 -L - (with 2 pre parasitic moults)
• Direct*: DH through and 2 parasitic
• Migratory Phase* Hepatic racheal using the bloodstream in liver, in vessels
• Lymphatic migration using steam

Summaries:

• Not always the best at identifying them
• Life cycle has a migratory / somatic state

Rhabditida

• Important group of nematodes
• Causative agents of infection
• Life Cycle*
• Infective film penetrates in the stratum with new generation in adult
• Infects filariform/and autofillaria

Key Features

• Infections from a variety of factors of the GIT
• Parasites in host-animal
• Diarrhoea, weight loss

Ancylostomatoidea

• *Higher in mammals.
• *Hook and tape Infection:
• Larvae infection from -transduces fluids or infection from milk Publicity: Man also gets infected through percutaneous infection leading to larva migrans

Ancylostoma. Species + Infections

• A variety of worms that infect by hooking from the surface of the skin

Cycle.Life and species

• Bloodstream is key to parasite reproduction
• Can be ingested through breast milk.
• In general:
• **

Ascaridida:

SuperFamilies: Ascaridoidea and other: large species

• Cycle: direct life Ascarid-type eggs: Thick, smooth, hard Eggs do not hatch externally
• Mammal Infection (Birds, Reptiles)*
• Infection and
• Transmammary by a milk-based transmission where eggs cannot be hatch

Species and DH:

Ascaris lumbricoides - (humans cross) DISTRIBUTION: Cosmopolitan

• Development:* Infection through eggs

CHARACTERS:

Subspherical + egg medium

• Epidemiology*. infection and immune from other side Young children and infection Ascarosis a pathogen " Ascariasis

Public: Health:

Hygiene important and for high water supplies

Toxocara, Infections + Species:

1. Direct to humans by eggs in intestine from animals

Eggs cannot Hatch

LifeStage, Distribution + Development:

• Distribution cosmopolitan
• Trans mammary.
• Parasitic development:
• Ingestion with eggs (2 -4 ) in body
• Demonstration :
• Immature egg
• Epidemiology:* 1 transmission (vertical) to hosts
• High resistance for longer

Enolplida "whipwarm

Most hosts get this from the consumption of eggs with the

• All and
• Host.