Helminths - A11CLS/20 - NLE

Helminths - A11CLS/20
Dr Steve Diggle
Royal Society Research Fellow
and Lecturer
School of Molecular Medical Sciences
Centre for Biomolecular Sciences
University of Nottingham
Aims: To understand the importance of helminthic disease in man
Objectives:
Outline the spectrum of helminths responsible for human disease
Outline the role of vectors in the life cycle of selected helminths
Distinguish helminthic infections that are restricted to the gut from those which invade the
tissues
Outline the different approaches to the laboratory diagnosis of helminthic infections
Explain the principles for the prevention of helminthic infections through vector control,
hygiene and sanitation and chemotherapy
Helminths (parasitic worms)
Definition:
Eukaryotic multicellular organisms which
reproduce sexually, usually within the host, but
have pre-adult stages (ova, larvae) which live
externally (or in other hosts)
Common helminths and helminthic diseases
Genus
•
•
•
•
•
•
•
•
•
•
•
Disease
Schistosoma
SCHISTOSOMIASIS
Ascaris
ASCARIASIS (Roundworm)
Ancylostoma/Necator
HOOKWORM
Enterobius
PIN (Thread worm)
Trichuris
TRICHURIASIS (Whipworm)
Taenia
TAPEWORM INFECTIONS
Echinococcus
HYDATID DISEASES
Trichinella
TRICHINOSIS
Strongyloides
STRONGYLOIDIASIS
Filariae
FILARIASES (e.g. Elephantiasis)
Onchocherca
ONCHOCERCIASIS (River blindness)
Classification of Helminths
Families
Trematodes
Cestodes
Nematodes
Flukes
Tapeworms
Roundworms
Examples
Schistosoma, Fasciola
Taenia solium (pork), T.
sagninatum (beef),
Echinococcus spp.
Ascaris, Hookworms,
Filariae
Shape
Unsegmented
Segmented
Cylindrical
Body cavity
No
No
Present
Digestive tube
Ends in cecum
No
Ends in anus
Hook organ
Oral and ventral sucker
Oral sucker, bortridas
and rostellar hooks
Lips, teeth, dentary plates
Sex
Hermaphroditic except
Schistosoma
Hermaphroditic
Dioecious (male and
female)
Comprises
Trematodes
Trematoda - Platyhelminths, Flukes
Flatworms although some are rounded in appearance
Zombie snail!
Flatworm
Leucochloridium paradoxum
Amber snail - intermediate host
Bird droppings - snail - bird
http://www.youtube.com/watch?v=EWB_COSUXMw
Trematode characteristics
•
•
2 suckers (oral and ventral)
•
•
Digenetic (2 hosts)
•
Rest is mainly for
reproduction
•
Hermaphrodites (self
fertilising, except
Schistosoma)
Oral sucker leads to blind
ending gut
Secretory system opening
into excretory pore
Schistosomiasis (Bilharzia)
•
Affects 200,000,000 people
worldwide
•
Largely in developing countries in
the tropics/sub tropics (rural areas)
•
Dams and irrigation systems have
encouraged spread
•
Chronic infection is a cause of
significant morbidity
•
3 species affect humans S. haematobium, S. mansoni, S.
japonicum
Schistosomiasis - global distribution of infecting species
From Center for Disease Control (CDC)
Schistosomiasis life cycle
Intermediate host
Male
Female
Schistosome cercaria
Schistosomiasis - General clinical features
• “Swimmers itch” at site of cercarial
penetration
• 4 weeks later - allergic reaction: fever, rash,
myalgia, pneumonitis (Katayama fever)
• Asymptomatic egg deposition (3 months)
S. mansoni - clinical features
• Blood stained diarrhoea
• Rectal ulceration and fibrosis
• Rectal strictures
• Hepatic fibrosis and portal hypertension
• Oesophageal varices and splenomegaly
S. haematobium - clinical features
• Painless, terminal haematuria
• Progressive bladder symptoms
• Recurrent UTI
• Fibrosis of ureters and bladder
• Renal failure
• Bladder carcinoma
Schistosomiasis - diagnosis
S. mansoni
Ova (lateral spine) in faeces or rectal snips
S. haematobium
Ova (terminal spine) in filtered mid-day
urine
Serology
- ELISA (Enzyme linked Immunosorbent Assay). Detects antigens and antibodies
- Supports the parasitological diagnosis
Schistosomiasis - treatment
Praziquantel (Biltricide) - Antihelminthic effective against flatworms
S. haematobium and S. mansoni
Praziquantel 40mg/kg single dose
S. japonicum
Praziquantel 60mg/kg single dose
Treatment is 90 % curative
Follow up samples of urine/faeces at 3 months
Cestodes
Cestoda - Tapeworms
Body arranged in identical individuals known as
proglottids
- Taenia solium (pork)
- Taenia saginatum (beef)
- Echinococcus granulosus
- Echinococcus multilocularis
Life cycle of the pork tapeworm (T. solium)
Scolex - attaches to intestine of definitive host
Definitive host
T. solium head and scolex
Pork tapeworm control
- Inspection of pork meat and removal of
infected carcasses
- Sanitary disposal of human faeces
Hydatid Disease (Echinococcosis)
•
Dog tapeworm (Echinococcus
granulosus). Adult lives in dog
small intestine
•
Intermediate host: Man.
Acquired by ingestion of cysts
from dog excreta
•
Dog: Acquires infection from
Sheep offal
•
Distribution: Middle East,
Australia, S. America, N. Wales
Hydatid Disease (Echinococcosis)
•
•
•
•
•
Formation of hydatid cysts primarily in liver and lungs
•
Rupture can lead to dissemination due to protoscolices
release
Cyst grows slowly (5-20 years)
Pressure of growing cyst often first sign of infection
In liver can cause biliary rupture
Rupture of cysts (20%) produce fever and possible
anaphylactic shock
Hydatid Disease - Life cycle
Hydatid cysts
Treatment: Surgery (remove cyst). Open cyst (treat with 2 %
formalin). Albendazole (kills protoscolices)
Roundworms (nematodes)
Extremely diverse: 28,000 species (16,000 parasitic)
Digestive system with tubes that open at both ends
Medically important nematodes: Ascaris, Enterobius, Hookworms, Trichinella, Trichuris,
Strongyloides, Filariae
Life cycle of Enterobius (thread or pin worm)
Sellotape on perianal skin first thing in the morning
Treatment is unsatisfactory if other members of house are infected. Prevention: personal cleanliness.
Mebendazole can be used
Life cycle of Ascaris lumbricoides (roundworm)
Ascariasis
Clinical symptoms:
- Usual 5-10 worms, unnoticed in host
- Abdominal pain
- Asthmatic attacks
- Severe: Adults can invade bile ducts, liver, pancreas (pancreatitis). Can be fatal
Diagnosis:
Eggs in faeces
Treatment:
Piperazine citrate. 2 days treatment will
eliminate 95 % of infection
Control:
Family hygiene; sanitary disposal of faeces
Difficult due to ignorance/poverty of population
Life cycle of Hookworm (Ancylostoma and Necator)
‘Main’ species in humans:
Ancylostoma duodenale (Mediterranean, Northern Asia,
South America)
Necator americanus (Western hemisphere, Central/
South Africa, Southern Asia, Australia)
A. duodenale
N. americanus
Hookworm infection
Clinical symptoms:
- Larvae: localised erythema and itching
- Gastroenteritis 6 weeks after infection
- Worms like upper small intestine. 0.1 ml blood/worm over 24 h
- Possible anaemia if worm burden is heavy (possible Pica)
- Infections can persist upto 8 years (A. duodenale) and 2 years (N. americanus)
- Daily egg output per female worm 10,000-20,000
Diagnosis:
- Clinical picture not sufficient
- Eggs in faeces
Treatment:
Mebendazole (100 mg. Twice daily for 3 days). Also effective against Ascaris. Also Albendazole
Control:
Sanitary disposal of faeces
Protection of susceptible individuals
Treatment of infected individuals (removes egg problem)
500 million people infected with hookworm
5 trillion eggs/day!
Filariases (nematodes)
• Several species affect humans
• Vectors - mosquitoes and other insects
• Adult worms reside in lymphatics or tissues
• Adult female releases microfilariae which
circulate in blood and tissues
• Chronic infection: tissue inflammation,
fibrosis, eosinophilia
Diseases caused by filarial worms
Organism
Wuchereria
bancroftii
Brugia timori/
malayi
Loa loa
Onchocerca
Adult worm
Lymphatics
Lymphatics
Subcutaneous
Subcutaneous
Microfilariae
Clinical signs
Distribution
Blood
Fever,
Lymphangitis,
elephantitis
Tropics
Blood
Fever,
Lymphangitis,
elephantitis
E & SE Asia, South
India, Sri Lanka
Blood
‘Calabar’ swellings,
eye migration,
Urticaria
W & Cent Africa
Skin, eye
Subcutaneous
nodules, eye
disease, blindness
Africa, S. America
Bancroftian filariasis (W. bancroftii)
Bancroftian filariasis
Clinical symptoms:
- Can be asymptomatic filariasis
- Obstructive filariasis (Elephantiasis is the dramatic endproduct (exception rather than rule)
- High protein content of the lymph stimulates growth of dermal/collagenous connective tissue
- Over many years these parts harden producing elephantiasis
Diagnosis:
- Patient history on exposure to mosquitoes
- Blood examined for microfilariae
- Serological test if microfilariae are absent from blood
Treatment:
Diethylcarbamazine (DEC). Eliminates microfilariae and kills adult worms
Control:
Protection against mosquito bites (clothing, repellant)
Reading list
•
•
•
NLE - CLS20 - further resources
•
•
Manson’s Tropical Diseases – Ed. G.C. Cook
Clinical Medicine – Kumar & Clark Chapter 2
Atlas of Medical Helminthology and Protozoology 4th ed. PL Chiodini
Markell & Voge’s Medical Parasitology - David T John &
William A Petri
[email protected]