Download Introducºon to Parasiºc Worms (Helminths)

Recently in the news Introduc)on to Parasi)c Worms (Helminths) 1
Introduc)on to Helminth Parasites Parasite
Diseases
Plasmodium
No. people infected
malaria
Soil transmitted helminths:
 
Roundworm (Ascaris)
Pneumonitis, intestinal obstruction
 
 
 
Whipworm (Trichuris)
Bloody diarrhoea, rectal prolapse
Hookworm (Ancylostoma
and Necator)
Coughing, wheezing, abdominal
pain and anaemia
Deaths/yr
273 million
1.12 million
>2 billion
200,000
Schistosoma
Renal tract and intestinal disease
200 million
15,000
Filariae
Lymphatic filariasis and
elephantiasis
120 million
Not fatal but 40
million
disfigured or
incapacitated
Trypanosoma cruzi
Chagas disease (cardiovascular)
13 million
14,000
African trypanosomes
African sleeping sickness
<100,000
<10,000
Leishamania
Cutaneous, mucocutaneous and
visceral leishmaniasis
12 million; 2 million new
cases/yr
50,000
Introduc)on to Helminth Parasites Sub
kingdom
Metazoa
Phylum
Class
Nematodes
Ascaris (roundworm)
Trichuris (whipworm)
Ancylostoma
(hookworm)
Necator (hookworm)
Enterobius (pinworm or
threadworm)
Strongyloides
C. elegans
Probably >1 mill species
25000 species described
Round worms; appear
round in cross section, they
have body cavities, a
straight alimentary canal
and an anus
Platyhelminthes
Flat worms; dorsoventrally
flattened, no body cavity
and, if present, the
alimentary canal is blind
ending
Genus –
examples
Cestodes
Taenia (tapeworm)
Adult tapeworms are found in
the intestine of their host
They have a head (scolex)
with sucking organs, a
segmented body but no
alimentary canal
Each body segment is
hermaphrodite
Trematodes
Non-segmented, usually leafshaped, with two suckers but
no distinct head
They have an alimentary
canal and are usually
hermaphrodite and leaf
shaped
Schistosomes are the
exception. They are threadlike, and have separate sexes
Fasciola (liver fluke)
Schistosoma (not leaf
shaped!)
2
Structure of nematodes (C. elegans) 100 µm
Nematodes Ascaris
• 
Formally they are bilaterally symmetrical, vermiform. • 
They have a thick complex cuCcle underlain by longitudinal muscles (but no circular muscles) • 
A pseudocoelom (blastocoelom), and a single cell-­‐layered gut running from the anterior mouth to a sub-­‐terminal anus. The pharynx is strongly muscular, with a triangular cross secCon, and sucks in liquid / micro-­‐parCculate food. There is no circulatory system, and the excretory system is very basic (neither flame cells nor nephridia, but unique structures called reneIe cells.) • 
• 
• 
• 
3
Nematodes • 
• 
Cuticle
Arguably the defining feature of the nematode body is its thick cuticle. All
nematodes have a thick collagen body wall retaining a high internal hydrostatic
pressure, up to half an atmosphere - they are almost impossible to squash under
normal circumstances. The design of the body wall is unique to the phylum. It
has up to 9 layers (typically 4), these fibres run in different directions, very much
like a high-pressure tyre. The fibres are inelastic, so preventing changes in body
volume while permitting lateral undulations. This high internal pressure defines
many aspects of the nematode’s life.
Thickness of cuticle: ~80 µm
Nematodes Feeding •  The gut is a tube lined by a single cell layer, with no muscles, but microvilli. Its transit Cme is very short, around 3 minutes, with the animals defecaCng conCnuously as fast as is compaCble with their hydrostaCc pressure. It is thought that this is too fast for much enzymaCc/digesCve acCon, and that they simply absorb useful nutrients without engaging in digesCon per se. 4
Nematodes •  The fundamental design is pre-­‐adapted to endo-­‐parasiCsm. •  1:The thick body wall is an excellent protecCon against chemical or immune aIack, allowing them to survive gut acids or anCbody aIack. (AnCbodies certainly do bind to nematode cuCcle, but can’t puncture it.) •  2: The vast numbers of resistant eggs allow dispersal in Cme and space, maximizing the chance of infecCng a new host. •  3: The microphagous habit pre-­‐adapts to a gut content / body fluid diet. •  4: The body design works well at small body size, which is advantageous for most parasiCc lifestyles (although some worms are up to 9 m in length). Nematode reproducCon •  Most Nematodes produce eggs in prodigious quanCCes (oviparous). A typical gut parasite releases 15,000 eggs per day. One such prolific producer the human hookworm Ancylostoma duodenale may shed eggs at this rate for all of its life of 5 -­‐ 15 years. •  Onchocerca does not produce eggs (viviparous). The first stage in its life cycle are live young called microfilariae. However, they are also produced in vast quanCCes. 50 µm
Taenia solium egg
50 µm
Trichuris egg
5
Life cycle of nematodes (C. elegans) •  normally male and female worms (dioecious/diözisch) •  occasionally hermaphrodites (e.g. C. elegans) •  4 larval stages (L1-­‐L4) •  adult worm about 1 cm in length Introduc)on to Helminth Parasites -­‐ Nematodes Trichuris (whipworm [Peitschenwurm])
•  A soil transmitted helminth
•  prevalent in warm, humid conditions
•  Can cause diarrhoea, rectal prolapse and anaemia
in heavily-infected people
Ancylostoma and Necator (hookworms [Hakenwurm])
•  A major cause of anaemia in the tropics
Strongyloides [Zwergfadenwurm]
•  inhabits the small bowel
•  infection more severe in immuno-suppressed
people (e.g. HIV/AIDS, malnutrition)
Enterobius (pinworm or threadworm [Madenwurm])
•  prevalent in cold and temperate climates but rare
in the tropics
•  found mainly in children – this is one YOU are
likely to have had in your own childhood
6
Enterobius vermicularis (pinworm, Madenwurm)Life Cycle Nematodes •  Ancylostoma duodenale – Hookworm (Hakenwurm) 7
Ancylostoma duodenale – Life Cycle (L3)
(L1-L2)
(L4)
Introduc)on to Helminthe Parasites -­‐ Hookworms Life cycle
 
 
 
 
 
 
 
 
 
 
Adult worms live in the intestine and excrete eggs in the
faeces
In the absence of latrines, eggs contaminate soil and
develop in warm, damp conditions (Grubenwurm)
eggs hatch and infective filariform larvae develop in
about one week and remain infective in soil for up to 3
weeks
filariform larvae penetrate the skin when a person walks
barefoot in the soil
Larvae migrate from the skin to the lungs via the
lymphatic and blood systems
Larvae penetrate the capillary wall to enter the alveoli
Larvae are propelled up the respiratory tree to the
epiglottis where they are swallowed
Develops to adult stage in upper intestine; adult worms
are fully mature after about 5 weeks
Infection load can be up to 1000 worms (average 50-100)
Eggs are excreted in the faeces
8
Introduc)on to Helminthe Parasites -­‐ Hookworms Pathology
 
 
 
 
 
 
Hookworms move several times a day to different
attachment sites in the upper intestinal mucosa to ingest
blood
They secrete an anticoagulant which causes the old
attachment sites to continue to bleed
Heavy hookworm infection results in chronic
haemorrhage from the duodenal and jejunal mucosa
The combination of constant blood loss due to hookworm
infection and poor iron intake in the diet results in iron
deficiency anaemia
In a child, the continued daily loss of 10ml of blood can
lead to severe anaemia
1000 worms can consume up to 500 ml blood per day
Introduc)on to Helminthe Parasites -­‐ Hookworm Symptoms and signs
Minor
 
Often itchy papules are found at the site where the larva
penetrated the skin
 
There may be cough and wheezing as the larva migrates
through the lungs
Major
 
Hookworm anaemia
•  Tiredness, aches and pains (stomach)
•  Breathlessness
•  Oedema
  Cardiac complications
Diagnosis
 
Microscopic examination of faecal smears to demonstrate
significant numbers of hook worm eggs
 
Measure Hb, serum ferritin, iron
 
Exclude other causes of anaemia
9
Introduc)on to Helminthe Parasites -­‐ Hookworm Treatment
 
 
 
 
Mebendazole (cheap) – 100mg, twice daily for 3 days
Mebendazole is contraindicated in pregnancy – use
Bephenium hydroxynaphthoate “alcopar”
Mebendazole (a benzamidine) destroys microtubules
For anaemia: ferrous sulphate 200-400 mg three times a
day for 3 months (adult regimen)
Prevention and control
  Health education and improve sanitation facilities –
install pit latrines
  Encourage use of protective footwear
  Mass drug treatment of communities
  Iron supplementation in areas of low iron intake
Introduc)on to Helminthe Parasites -­‐ Hookworms Epidemiology
 
 
>1200m infections each year of which 100m are
symptomatic
It is due to 2 parasites both of which occur worldwide:
•  Necator americanus - predominant species in subSaharan Africa, south Asia and the Pacific
•  Ancylostoma duodenale –predominant in S. Europe,
N. Africa, western Asia, northern China, Japan and
the west coast of America
10
Introduc)on to Helminthe Parasites -­‐ Nematodes Ascaris (roundworm [Spulwurm])
•  Found world-wide in conditions of poor hygiene,
transmitted by the faecal- oral route
•  Adult worms lives in the small intestine
•  Causes eosinophilia
Filarial Worms including:
 
 
 
Onchocerca volvulus – Transmitted by the simulium
black fly (Kriebelmücke), this microfilarial parasite can
cause visual impairment, blindness and severe itching
of the skin in those infected
Wuchereria bancrofti – The major causative agent of
lymphatic filariasis
Brugia malayi – Another microfilarial parasite that
causes lymphatic filariasis
Ascaris –Life Cycle • 
• 
• 
• 
• 
• 
• 
• 
• 
• 
• 
Eggs are ingested
L3 larvae hatches in
intestines
Penetrate gut wall into
blood
Migrate to liver
Mold into L4 larvae
Transport via vena cava to
heart and lung
Penetrate alveolae
Passiv transport up
airways
Swallowing, transport to
small intestine
Develop into adult worms
Eggs are excreted
11
Nematodes •  Ascaris – Heavy InfestaCon Introduc)on to Helminthe Parasites -­‐ Nematodes Toxocara canis & cati (Hunde/Katzen-Spulwurm)
• 
• 
• 
A world-wide infection of dogs and cats
Human infection occurs when embryonated eggs are
ingested from dog or cat faeces (eggs can be
infectious for up to 2 years) sandpits
It is common in children and can cause visceral
larva migrans (VLM)
• 
Dead larvae cause inflammations and granulomas
• 
If eyes are infected, blindness can occur
• 
• 
Human is a paratenic host (parasites survives but
doesn’t undergo further development)
Deworm your cats and dogs regularly!
12
Toxocara canis Introduc)on to Helminth Parasites -­‐ Filarial Worms Some species cause Elephan)asis 13
Introduc)on to Helminthe Parasites -­‐ Filarial Worms Symptoms and signs – 3 stages
1. Asymptomatic stage
  There is internal damage to the lymphatics and kidneys
2. Acute stage – Filarial lymphangitis (inflammation)
  Characterised by bouts of fever
  heat, redness, pain, swelling and tenderness of the
lymph nodes and ducts
3. Chronic stage
  Usually results in elephantiasis as a result of chronic
lymphoedema (=lymphatic obstruction)
  There is a massive overgrowth of tissue resulting in
severe deformities
  The legs are often affected and result in inability to walk
  The scrotum is often affected in men and the breasts
and vulva in women
Introduc)on to Helminthe Parasites -­‐ Filarial Worms MoldL4 larvae
Up to 108 filaria in heavy infections
14
Nematodes •  Simulium (Blackfly[Kriebelmücke]) – Vector for Onchocerca volvulus •  Feeds on blood and
tissue
•  Takes up subcutaneous
microfilaria
Nematodes •  Onchocerca Microfilaria
Length: ~300 µm
Nodule (Onchocercoma)
with adult worms
Length: 25 (males)-50 cm (females)
15
Nematodes •  Onchocerca nodule Nematodes •  Onchocerca volvulus – The cause of River Blindness 16
Filarial worms – Wuchereria bancroci/Brugia malayi •  Transmitted by mosquitos
•  Reside in blood & lypmphatic
system
•  Periodicity of appearnace of
microfilaria in the blood
•  Peak between 10 pm and 2
am
•  Night-feeding mosquitoes are
main vectors
•  During daytime microfilaria
are mainly in pulmonary
arteries (high O2)
•  Change in sleep pattern
reverses periodicity from
nocturnal to diurnal
•  Cause of lymphatic filariasis
(Elephantiasis)
•  No known animal reservoir
hosts
Introduc)on to Helminthe Parasites -­‐ Filarial Worms Diagnosis
 
 
 
Microscopic examination of Giemsa stained thick blood
films for the presence of microfilariae
W. bancrofti shows marked nocturnal periodicity, so it’s
best to collect blood samples between 10pm and 1 am
Serology
Treatment
  Diethylcarbamazine (DEC) rapidly kills microfilariae and
will kill adult worms if given in full dosage over 3 weeks
  Release of antigens from dying microfilaria causes
allergic-type reactions – add an antihistamine and
aspirin to treatment regimen
  Other treatment options are
• 
ivermectin
• 
combination of DEC and albendazole
17
Introduc)on to Helminthe Parasites -­‐ Filarial Worms Prevention and control
 
 
 
 
Rapid diagnosis and treatment of infected individuals
Mass drug administration to at risk communities
Vector control: eliminate mosquito breeding sites
through improved sanitation and environmental
management
Personal protection against mosquito bites by
insecticides, bed nets and repellents
18