Zoonotic Cestodes Flashcards
What is the scolex of a Echinococcus granulosus?
The head
How would you describe using one word a cestode carrying eggs?
Gravid
Give some info on the eggs when theyre in the environment?
Irregular dispersion and contamination of areas from the DH
Additional dispersion through vectors (flies/birds) and other factors (rain)
Highly resistent eggs 20C for 2 months, below 1C for 6 months
Susceptible to dryness
What are metacestodes?
Always in an intermidiate host
Hydatid cysts
Exansive development
Asexual production
Hydatid sand: metacestodes in clusters: feels likfe grains of sand
Where do hytatid cysts form in sheep cows and horses
Sheep: liver and lungs
Cows: Lungs
Horses: Liver
Give an overview of the E. granulosus life cycle?
Egg Stage: Infective stage for intermediate host.Adult tapeworms reside in small intestine of definitive host (canis), Mature Gravid Progllottids detach from adult and pass by fecaes, Release eggs to environment
Ingestion by an intermediate host: Intermediate host (sheep etc) become infected when ingest food water etc with contaminated eggs, Eggs hatch in S intesitne releasing oncospheres (larval forms), These penetrate the intestinal wall and enter the blood stream ot lymph system
Larval development in intermediate Host: Larvas migrate to specific organs then lodge into the tissue they develop hydatid cycts, numerous protoscolices form within brood capsules over months to years
Ingestion by definitive host: Canines become infected by consuming infected rae offal (organs) from infected intermediate, inside the canine undergoes evagination and attaches the intestinal wall
Development into Adult Tapeworm: The protoscolices mature into adult tapeworms within 4-6weeks, and then the cycle resets/carries on.
How does ingestion lead to protoscolex evagination?
They become everted making the hooks and suckers to be outside and able to hook onto the intestinal wall
What are the common points with different E.gran strains?
Cattle sheep cervid pig and camel strains all have canines as the definitive hosts the others are intermediate hosts, Humans are only accidental intermediate hosts
The horse strain is the only one that doesnt affect humans
What happens in the G1 sheep strain (sensu stricto)?
Sheep main intermediate host
Lungs are the primary site for dev
Liver is also important
Eggs also infective for cattle and humans
An important zoonosis
Occurs mainly in part of Wales (not Ireland)
Flocks graze–>hydatid cyst in sheep
–>Dogs scavenge dead sheep
—>Adult tapeworm in dogs
—>Dogs defaecate near the homestead
What is G4 ECHINOCOCCUS eQUINUS?
Horses are the only intermediate hosts
Was common in rural england as hunt kennels disseminated eggs
Fed horse meat
Present in Ireland
Liver is the primary site of dev
Eggs appear to be non-infective for humans: No human cases reported so far, Failure to infect non-human primates
Discuss the general principles of control of E. granulosus?
Control of E. granulosus
Ø Base-line epidemiology (prevalence)
Ø Dog registration
Ø Regular treatment (praziquantel)
Ø Education (farmers + dog owners)
Ø Regular screening
Ø Minimise dog access to raw offal/intermediate hosts, clean up dog faeces
Ø Good dog food production
Ø Reduce dog access to grazing areas
Legislation
Discuss the public health importance of E. granulosus?
Human Health impacts
Cystic Echinococcosis (CE) in Humans
Clinical Manifestations
Liver Cysts (70% of cases) → Can cause abdominal pain, jaundice, and hepatomegaly.
Lung Cysts (20-30%) → May lead to chest pain, coughing, and breathlessness.
Brain, Heart, or Bone Involvement (Rare but Severe) → Neurological symptoms, cardiac failure, or bone fractures.
Ruptured Cysts → Can cause anaphylactic shock, secondary cyst formation, or bacterial infection.
Diagnosis and Treatment
WHO classifies CE as a neglected tropical disease (NTD)
Livestock Losses
Medical Costs
Transmission and Risk Factors
Devise strategies to (a) control; and (b) monitor infection of both animals and humans with Echinococcus;
Prevention and Control Strategies
(a) Dog Deworming Programs
Regular anthelmintic treatment (praziquantel) for dogs to eliminate adult worms.
(b) Proper Disposal of Infected Offal
Prevent dogs from consuming raw livestock organs.
(c) Public Awareness and Hygiene Education
Promoting handwashing, safe food handling, and avoiding dog feces contamination.
(d) Livestock Vaccination
EG95 vaccine for sheep to reduce cyst formation and transmission.
(e) Improved Sanitation and Meat Inspection
Routine meat inspections to detect and remove infected organs. Access to clean drinking water and proper waste disposal.
Discuss what parasite control should be used other than just drug treatment?
(a) Veterinary and Animal Management
Regular deworming of definitive hosts (e.g., dogs for Echinococcus granulosus). Improved animal husbandry to minimize parasite exposure. Proper disposal of infected offal to prevent ingestion by scavenging animals. Vaccination programs (e.g., EG95 vaccine for livestock against E. granulosus).
(b) Environmental Control
Proper waste management to prevent fecal contamination of food and water. Vector control programs (e.g., reducing mosquito breeding sites for malaria prevention). Improved sanitation infrastructure (e.g., latrines, sewage treatment) to reduce egg and larval spread.
(c) Public Health and Hygiene Education
Handwashing campaigns to minimize fecal-oral transmission of parasites. Safe food handling (e.g., cooking meat thoroughly to kill larval stages). Health education in schools and communities to promote awareness of parasite transmission.
(d) Surveillance and Early Detection
Regular screening programs to detect and treat infections before they spread. Monitoring animal and human infection rates to guide control efforts. Meat inspection to identify and remove infected carcasses from the food supply.
(e) Policy and Societal Interventions
Stronger regulations on livestock movement to prevent parasite spread. International collaboration for cross-border parasite control (e.g., E. granulosus in nomadic livestock communities). Economic incentives for farmers to implement parasite prevention strategies.
Why Drug Treatment Alone Is Insufficient?
Reinfection Risk: Treated individuals can quickly become reinfected if the environment remains contaminated.
Drug Resistance: Over-reliance on antiparasitic drugs can lead to resistance in parasites. Asymptomatic Carriers: Many infections persist in populations without noticeable symptoms, fueling transmission. Complex Life Cycles: Many parasites have multiple hosts (e.g., E. granulosus in dogs and livestock), requiring multi-level interventions.
