Helminths II Flashcards
Cestodes (tapeworms)
- Taenia saginata (beef tapeworm)
- Taenia solium (pork tapeworm)
- Diphyllobothrium latum (fish tapeworm)
- Hymenolepis nana (dwarf tapeworm)
- Echinococcus granulosus and multilocularis (hydatid cyst)
Cestodes
- Live in the intestine of their host
- Lack GI tract
- Hermaphrodites (male and female organs in the same tapeworm)
- Chain of box-like segments (proglottids)
- Each tapeworm consists of:
1 Scolex: has suckers and sometimes hooks
2 Immature proglottids
3 Mature proglottids have both male and female organs
4 Gravid proglottids contain fertilized eggs
Cestodes Life Cycle
- Adult worm lives in the GI tract of the definitive host (human)
- They produce proglottids and eggs that pass out in feces
- Eggs are ingested by the intermediate host where larvae develop in tissue
- The intermediate host is an animal that serve as food for the final host
- Clinical effects depend on whether humans are definitive hosts or intermediate hosts
- Tissue cysts, not intestinal worms, cause serious disease
Taenia saginata (beef tapeworm)
1•0 meters, 2000 proglottids
- Humans (definitive host) get infected from eating larval cysticerci in undercooked beef muscle (intermediate host)
- Adult uses suckers to adhere on small intestinal mucosa
- Clinical features: asymptomatic or malnutrition
- Diagnosis: identifying eggs or proglottids in feces
- Treatment: niclosamide or praziquantel
Taenia solium (pork tapeworm)
- 2-8 meters
- Humans (definitive host) get infected from eating larval cysticerci in undercooked pork muscle (intermediate host)
- Adult uses hooks in its scolex to attach to the intestinal mucosa
- Clinical features: asymptomatic
- Diagnosis: identifying eggs or proglottids in feces
- Treatment: niclosamide or praziquantel
Cystercercosis
- Cystercercosis occurs when humans play the role of the pig (intermediate host) by ingesting eggs (from another human stool)
- These eggs hatch within small intestine, and the larvae migrates throughout the body (mostly muscles and CNS), forming cystercerci
- Seizures, hydrocephalus, focal neurologic abnormalities
- Diagnosis: serology, imaging showing calcified cystercerci, or biopsy
- Treatment: albendazole or praziquantel for non- calcified (viable) CNS lesions. Corticosteroids are generally added. Treatment might exacerbate seizures.
Diphyllobothrium latum (fish tapeworm)
- 45 meters
- Acquired by ingesting larvae in raw freshwater fish (2nd intermediate host)
- Adult in human (definitive host) drop off their broad proglottids loaded with eggs
- Man-freshwater-crustacean-fish
- Adult worm absorbs B12 leading to B12 deficiency
- Diagnosis: eggs in stool
- Prevention: Thorough cooking, or freezing -10°C
Hymenolepis nana (dwarf tapeworm)
- Most common tapeworm
- 15-50 mm in length
- 4% of US school children
- No intermediate host
- Fecal oral spread
- Eggs hatch in the intestine; larvae penetrate the mucsoa-cystercercoid; come back out in the lumen as adults in the ileum; pass eggs
- Eggs are then ingested by humans
Echinococcus granulosus (hydatid disease- cystic echinococcus)
- 5mm in length. Common worldwide
- Navaho reservation of southern UT and northern AZ
- Dogs are the definitive host
- Sheep and human (intermediate host) became infected by ingesting eggs from dog stool
- Larvae in sheep or human take the form of large fluidfilled collections called hydatid cyst in the liver or, less likely the lung and brain
- Dogs acquire infection by eating sheep with hydatid cyst
Echinococcus granulosus (hydatid disease- cystic echinococcus) Clinical Features
•asymptomatic, palpable liver cyst, anaphylaxis (in cases of cyst rupture)
Echinococcus granulosus (hydatid disease- cystic echinococcus) Diagnosis
•imaging- immunoelectrophoresis
Echinococcus granulosus (hydatid disease- cystic echinococcus) Treatment
•Albendazole
- Avoid cyst puncture (anaphylaxis)
- New technique- PAIR (puncture, aspiration, injection, reaspiration)
•Prevention: dog deworming, not allowing them to feed on sheep, washing hands after contact with dogs, and burning or burying infected carcasses
Echinococcus multilocularis (alveolar echinococcus)
- Foxes, coyotes, and rarely domestic dogs
- North America, Europe and Asia
- Increasing prevalence in the US
- E. multilocularis bud externally, producing proliferative, multilocular cysts that slowly invade and destroy organs
- Liver failure- high mortality
Trematodes
Paragonimus westermani (lung fluke)
- Humans ingest inadequately cooked crabs/crayfish containing metacercariae
- Southeast Asia: sushi
- Adults live and mate in alveoli
- Eggs passed in the sputum; cough and chest pain
- Lung cysts
- Rupture into bronchioles, pleural fluid, bacterial infection
- Peripheral eosinophilia
- Diagnosis: eggs in sputum, pleural fluid or feces- serology
- Treatment: praziquantel
- Paragonimus kelicotti
Liver flukes
•Clonorchis sinensis, Opisthorchis felinieus
- Transmission: Eating contaminated fish (metacercariae inside fish)
- Adult worm migrates to the liver -> recurrent cholangitis, pigmented gallbladder stones, cholangiocarcinoma
•Fasciola hepatica
- Transmission: metacercariae on water plants ingested by human
- Adult worm migrates to the liver-> hepatomegaly.
- The only fluke that does not respond to praziquantel. Use triclabendazole
Intestinal flukes (Fasciolopsis buski)
- Transmission: metacercariae on water plants ingested by human
- Adult worm migrates to the intestine -> abdominal pain/ulceration
Schistosoma
- Second cause of sickness in the tropics (after malaria)
- Found in freshwater
- Cercariae penetrate exposed skin and invade venous system, where they mate and make eggs
- Eggs must reach fresh water to hatch
Schistosoma Pathogenesis
- Adult worms contribute little. They are not killed by host. This is thought to be due to molecular mimicry.
- Immune response of host against larvae and eggs is key
- Pulmonary migration
- Aberrant migration
- CNS (S. japonicum)
- Spinal cord
Schistosoma 3 Diseases
•Swimmers itch
-2 hours
•Swimmers fever
-2 weeks
•Symmer’s fibrosis
-2 years
Schistoma Swimmers itch- Cercarial dermatitis
- Urticaria and rash after cercariae penetration
- Worse with reexposure
- Most severe in persons infected with schistosomes of birds (avian), which die in the skin
- Fresh water lakes and Great Lakes support appropriate snails as intermediate hosts
- Wading birds
-Great Blue Heron
Schistoma Katayama fever (swimmer’s fever- acute schistosomiasis)
- Multisystem disease 2-12 weeks after exposure
- Low egg production
- Fever
- Respiratory symptoms
- GI symptoms
- Hepatosplenomegaly
- Eosinophilia
Chronic schistosomiasis
- Related primarily to immune response to eggs leading to fibrosis
- Disease associated with egg burden
- S. japonicum, S. mansoni:
- Portal hypertension
- Associated with and worsened by co-infections (hepatitis B and C)
•S. haemtobium:
- Bladder scarring with calcification
- Squamous cell carcinoma (SCC) of the bladder
- Associated with chronic Salmonella bacteriuria
Schistoma Diagnosis
•Clinical suspicion
-History- Eosinophilia
- Egg detection from urine or stool (can be negative in acute disease)
- Enzyme immunoassay (EIA)- detection of antigens in blood and urine
- Serology
- Liver or bladder imaging
Schistoma Treatment
- Praziquantel
- Steroids for inflammatory response
- Treatment will not reverse the scarring and won’t help in burned out infection
Schistoma Prevention
•Sanitary disposal of feces; use of molluscicides; multipronged approach; vaccine under development
