Epidemiology and control of helminth parasites.

What is EPIDEMIOLOGY?
 It is the study of distribution of diseases in a particular
community or district.
 Study and analysis of patterns, causes and effects of health
and disease state in particular population.
 The data are best obtained either directly in a field or from
a source such as hospitals or regional health clinic records

Classification:
• Epidemiology of parasites are mainly divided into 2 types:
 Protozoan Epidemiology and Helminthic Epidemiology

HELMINTHS
What are Helminths?
 Helminths (Greek meaning worms)
 Helminths are mostly parasitic worms ; but some are free
living.

CLASSIFICATION OF HELMINTHS
Two major phyla of helminths:
 NEMATHELMINTHES (Roundworms): Includes major
intestinal worms like soil-transmitted helminths Ascaris,
and the filarial worms that cause lymphatic filariasis.
 PLATYHELMINTHES (Flatworms): Includes two classes
 TREMATODA (Flukes) Leaf like; e.g., Schistosomes and
Fasciola
 CESTODA (Tapeworms) Ribbon like; e.g., Pork tapeworm
that causes Cysticercosis.

HELMINTH INFECTIONS
Roundworm infection(Nematodiasis):
Filariasis (Wuchereria bancrofti, Brugia malayi infection)
Onchocerciasis (Onchocerca volvulus infection)
Also known River blindness or Robles disease.
Soil-transmitted nematode disease:
It includes ascariasis (Ascaris lumricoides infection).
It is an intestinal roundworm.

Tapeworm Infection (Cestodiasis):
Echinococcosis (Echinococcus infection):
Infection through ingestion of parasitic egg with
contaminated food, water or soil.
Hymenolepiasis (Hymenolepis infection):
Caused by the introuction of tapeworm species;
Hymenolepis nana or Hymenolepis diminuta.
Taeniasis/ Cysticercosis (Taenia infection):
Acquired by humans through ingestion of tapeworm larval
cysts (cysticerci) in undercooked pork or beef.

Trematode infection (Trematodiasis):
Schistosomiasis/Bilharziasis (Schistosoma Infection):
Caused by parasitic worm that live in certain types of
freshwater snails.
 Amphistomiasis (Amphistoma infection):
It can be transmitted via penetration of skin or by direct
ingestion through contaminated food or water.
Fascioliasis (Fasciola infection)
It is a water and food borne zoonotic disease
Caused by two parasites: F. Hepatica and F. Gigantica.

PREVALENCE OF HELMINTHISIS
 Roundworm infected diseases:
FILARIASIS:
Caused by Wuchereria bancrofti, Brugia malayi
GLOBAL SCENERIO:
 An estimated 120 million people in tropical and subtropical
areas of the world are infected with lympathic filariasis; of
these, 25 million men have genital disease (most commonly
hydrocoele) and almost 15 million; mostly women, have
lymphoedema or elephantiasis of the leg.

 A recent study suggests that during the past 13 years >96.71
million cases were prevented or cured with MDA
(Methylenedioxyamphetamine) treatment, yet, as many as
36 million cases of hydrocoele and lymphoedema remain.
 Of the total population requiring preventive
chemotherapy, 57% live in South-East Asia region(9
countries), 37% live in African region (35 countries).
 One of the leading causes of global disability LF
(Lympathic Filariasis) accounts for 2.8 million DALYs
(Disability Adjacent Life Year).

INDIAN SCENERIO:
 A district-level endemicity map created in India in the year
2000, shows that of the 289 districts as many as 257 were
found to be endemic.
 About 553 million people are exposed to risk of infection;
and of them about 146 million live in urban and the
remaining in rural areas.
 About 31 millions are estimated to be carriers and over 23
million suffer from filarial disease menifestations in India.
 B. Malayi is prevalent in the states of Kerela, Tamil Nadu,
Andhra Pradesh, Madhya pradesh, Orissa, Assam, West
Bengal.

 Bihar has highest
endemicity (over
17%) followed by
kerela(15.7%) and
Uttar
Pradesh(14.6%).
 Andhra Pradesh and
Tamil Nadu Has
About 10%
endemicity.
 Goa showed the
lowest endemicity
(>1%), followed by
Lakshwadeep
(1.8%), Madhya
Pradesh(above 3%)
and Assam (5%).

ONCHOCERCIASIS (River Blindness):
Caused by Onchocera volvulus
Symptoms include itching, bumps under skin, blindness.
GLOBAL SCENERIO:
o About 37 million people are infected with this parasite,
about 300,000 of those have been permanently blinded.
o According to 2002 WHO report, Onchocerciasis has not
caused a single death, but its global burden is 987,000
Disability Adjusted Life Years (DALYs).

 As of 2008, about 99% of Onchocerciasis cases occurred in
Africa, and it is currently endemic in 30 African countries,
Yemen and isolated regions of South America.
 Infection reduces the host immunity and resistance to
other diseases, which results in an estimated reduction in
life expectancy of 13 years.
 This disease is not prevalent in India.

ASCARIASIS:
Most common helminthic human infection worldwide,
causative agent Ascaris lumbricoides.
GLOBAL SCENERIO:
 Highest prevalence in tropical and sub-tropical regions
where warm wet climates provide environmental
conditions that favour year-round transmission of infection
and areas with inadequate sanitations where suboptimal
sanitation practices lead to increased contamination of soil
and water.

 In United States ascariasis is the third most frequent
helminth infection exceeded only by hookworm and
Trichuris trichura (whipworm).
 1.4 billion of the population i.e 25% are infected with A.
lumbricoides.
 Ascariasis is found mostly in Asia(73%), Africa (12%),
South America (8%).
INDIAN SCENERIO:
 High prevalence rates are found in Tamil Nadu(85%) and
Kashmir (70%).

 The following table shows the prevalence of roundworm
infection as reported by some workers from different parts
of India:

 PREVALENCE OF TAPEWORM INFECTION
(CESTODIASIS):
 Prevalence of Echinococcosis (Echinococcus Infection:
 GLOBAL SCENERIO:
 Greatest infection is found in the temperate zones
including several parts of Eurasia (the Mediterranean
regions, Southern and Central parts of Russia, central Asia
and China), Australia, some parts of America and
Northeast Africa.

 Worldwide distribution of the zoonotic strains of
Echinococcus granulosus and geographical
endemicity.

 INDIAN SCENERIO:
 The disease is endemic in India.
 High prevalence is reported from Kashmir, Andhra
Pradesh, Tamil Nadu and Central India.

Prevalence of Hymenolepiasis (Hymenolepis infection):
 GLOBAL SCENERIO:
 The prevalence of H. nana in remote communities in
Northwest Australia is remarkably high, 55%.
 In Bat Dambang, Cambodia middle school students were
found to have a 2.4% prevalence.
 In 2006, a study in rural mexico found that 25% of the
children ages 6-10 in 12 schools were infected with H.
nana.
 Zimbabwe children in both small town and high-density
suburbs suffer from H. nana.

 Studies reported an overall prevalence rate of 24%in urban
areas and 18% prevalence in rural towns.

Prevalence of Taeniasis/Cysticercosis (Taenia infection)
GLOBAL SCENERIO:
 More than 80% of the world’s 50 million people who are
affected by epilepsy live in low- and lower-middle-income
countries.
 T. solium is the cause of 30% of epilepsy cases in many
endemic areas where people and roaming pigs livein close
proximity.

Figure: Endemicity of cysticercosis around the world

INDIAN SCENERIO:
 Cysticercosis is prevalent in virtually in all states of India,
except in Kerela and Jammu and Kashmir.
 NCC(Neural Cysticercosis) accounts for anywhere between
8.7 to 50% of patients presenting with recent onset of
seizure.
 The peculiarity of the disease in India is the high incidence
of patients with the solitary form of the disease, namely,
Solitary Cysticercus Granuloma (SCG).
 Pig rearing communities of the northern state of Uttar
Pradesh reported that 38% of the members of that
community has evidence of taeniasis.

 The prevalence of Taeniasis is probably in Northern than in
Southern areas.
PREVALENCE OF TREMATODE INFECTION
(TREMATODIASIS):
SCHISTOSOMIASIS/ BILHARZIASIS:
 It is considered second only to malaria as the most
devastating parasitic disease in the tropical countries.
 In Sub-Saharan Africa, more than 2000 deaths per year are
due to schistosomiasis.

Figure: Prevalence of schistosomiasis showing the non
endemic and endemic areas in world

Schistosoma mansoni:
 Distributed throughout Africa.
 Transmission also occurs in the Nile river valley in Sudan
and Egypt, South America: including Brazil, Suriname,
Venezuela Caribbean(low risk): Dominican Replublic,
Guadeloupe, Martinique and Saint Lucia.
Schistosoma Haematobium:
 Distributed throughout Africa: Southern and Sub-Saharan
Africa including the great lakes and rivers as well as smaller
bodies of water.
 Transmission also occurs in the Mahgreb region of North
Africa.

Schistosoms japonicum:
 Found in Indonesia and parts of China and South-East
Asia.
Schistosoms mekongi:
Found in Cambodia and Laos.
Schistosoma Intercalatum:
Found in parts of central and West Africa.
FASCIOLIASIS (Fasciola infection):
 Human Fasciolasis has been reported from countries in
Europe, America, Asia, Africa and Ocenia
 The incidence of human cases has been increasing in 51
countries of the 5 continents.

 In Europe, human fasciolosis occurs mainly in France,
Spain and Portugal.
 In Mexico, 53 cases have been reported.
 In Central America, the Caribbean Island, especially in
zones of Puerto Rico and Cuba
 In South America; Bolivia, Equador and Peru are highly
infected

INTENSITY OF SOME MAJOR
HELMINTHIASES:
SCHISTOSOMIASIS:
 S. haematobium infection intensity reduces with age
 Children are more highly affected and infected than adults
 Low infection probability for males than in females
 The incidence is usually more among those people who
constantly get in contact with the schistosome infected
waters through activities such as farming, fishing,
swimming and washing.
 Death rate is very low or negligible.

FILARIASIS:
 Repeated mosquito bites over several months to years are
needed to cause Lympathic Filariasis.
 This disease cause a negligible death rate but it can cause
permanent disabilities
 It affects both males and females
ASCARIASIS:
 It infects all ages of human. But mostly children of 2-10 year
of age and intensity decreases over 15 years of age.
 Most prevalent in areas of low socioeconomic status and
thus poverty and malnutrition
 It exerts a chronic effect on host nutrition.

TAENIASIS/CYSTERCOSIS:
 Most often in rural areas of developing countries, where
pigs roam freely and eat human faeces and where
hygiene practices are poor
 Worldwide as of 2010 it caused about 1,200 deaths, up
from 700 in 1990.
 The mean age at death was 40.5 years (range 2–88)
 The 33 US-born persons who died of cysticercosis
represented 15% of all cysticercosis-related deaths. The
cysticercosis mortality rate was highest in California,
which accounted for 60% of all cysticercosis deaths

 ECHINOCOCCOSIS:
 Cystic echinococcosis is rarely fatal. Occasionally, deaths
occur because of anaphylactic shock or cardiac tamponade
in heart .
 Hydatid disease is seen in subjects of any age and sex,
although it is more common in those aged 20–40 yrs
 It is a disease of rural areas where farming is practiced
traditionally.

SCHISTOSOMIASIS:
The manifestations of schistosomal infection vary over time
as the cercariae, and later adult worms and their eggs migrate
through the body.
Dermatitis
 Itchy papular rash
 1-3cm big round bumps
 The rash can occur between the first few hours and a week
after exposure and lasts for several days.
CLINICAL SYMPTOMS,
MORPHOLOGICAL AND PHYSICAL
ALTERATIONS

 A similar, more severe reaction called "swimmer's itch"
reaction can also be caused by cercariae from animal
trematodes that often infect birds.
Katayama fever:
 Acute schistosomiasis (Katayama fever) may occur
weeks or months after the initial infection as a
systemic reaction against migrating schistosomulae as
they pass through the bloodstream through the lungs
to the liver.

 Symptoms include:
 Dry cough with changes on chest x-ray
 Fever
 Fatigue
 Muscle aches
 Malaise
 Abdominal pain
 Enlargement of both the liver and the spleen
 The symptoms usually get better on their own but a small
proportion of people have persistent weight loss, diarrhea,
diffuse abdominal pain and rash.

Chronic Disease:
 In long established disease adult worms lay eggs that
can cause inflammatory reactions
 The long term manifestations are dependent on the
species of schistosome as the adult worms of different
species migrate to different areas.
 Many infections are mildly symptomatic, with anemia
and malnutrition being common in endemic areas.
Genitourinary disease:
 The worms of S. haematobium migrate to the veins
around the bladder and ureters

 This can lead to blood in the urine 10 to 12 weeks after
infection.
 Over time, fibrosis can lead to obstruction of the urinary
 Bladder cancer diagnosis and mortality are generally
elevated in affected areas, and have efforts to control
schistosomiasis in Egypt have led to decreases in the
bladder cancer rate. tract, hydronephrosis and kidney
failure.
 The risk of bladder cancer appears to be especially high in
male smokers, perhaps due to chronic irritation of the
bladder lining allowing it to be exposed to carcinogens
from smokin
 In women, genitourinary disease can also include genital
lesions that may lead to increased rates of HIV
transmissiong

Gastrointestinal Disease:
 The worms of S. mansoni and S. japonicum migrate to
the veins of the gastrointestinal tract and liver.
 Eggs in the gut wall can lead to pain, blood in the
stool, and diarrhea (especially in children).
 Severe disease can lead to narrowing of the colon or
rectum
 Eggs also migrate to the liver leading to fibrosis in 4 to
8 percent of people with chronic infection, mainly
those with long term heavy infection.

Central Nervous system disease
 Central nervous system lesions occur occasionally.
 Cerebral granulomatous disease may be caused by
S. japonicum eggs in the brain.
 Communities in China affected by S. japonicum have
been found to have rates of seizures eight times higher
than baseline.
 Similarly, granulomatous lesions from S. mansoni and
S. haematobium eggs in the spinal cord can lead to
transverse myelitis with flaccid paraplegia.

FILARIASIS:
 Elephantiasis affects mainly the lower extremities,
while the ears, mucous membranes, and amputation
stumps are affected less frequently
 Wuchereria bancrofti can affect the legs, arms, vulva,
breasts, and scrotum (causing hydrocele formation),
while Brugia timori rarely affects the genitals.
 Those who develop the chronic stages of elephantiasis
are usually amicrofilaraemic, and often have adverse
immunological reactions to the microfilariae, as well
as the adult worms.

 The list of signs and symptoms mentioned in various
sources for Lymphatic Filariasis includes the 31
symptoms listed below: (major)
 Swollen lymph nodes ,Lymphedema ,Swollen armpit lymph
nodes ,Swollen groin lymph nodes ,Arm swelling ,Breast
swelling ,Leg swelling ,Male genital swelling ,Elephantiasis
,Lymphangitis ,Fever ,Aches ,Pain ,Epididymitis ,Orchitis
,Eosinophilia ,Hydrocele ,Chyluria , Thickened skin

ASCARIASIS:
 Most people who are infected with only a small number of
worms have no symptoms.
 Clinical features depend on the affected body site
 Migrating larva:
 As larval stages travel through the body, they may cause
visceral damage, peritonitis and inflammation,
enlargement of the liver or spleen, and an inflammation of
the lungs.
 Pulmonary manifestations take place during larval
migration and may present as Loeffler's syndrome, a
transient respiratory illness associated with blood
eosinophilia and pulmonary infiltrates with radiographic
shadowing

 Intestinal blockage:
 The worms can occasionally cause intestinal blockage when
large numbers get tangled into a bolus or they may migrate
from the small intestine, which may require surgery.
 More than 796 A. lumbricoides worms weighing up to 550 g
[19 ounces] were recovered at autopsy from a 2-year-old
South African girl. The worms had caused torsion and
gangrene of the ileum, which was interpreted as the cause
of death

 Bowel obstruction:
 Bowel obstruction may occur in up to 0.2 per 1000
per year.
 Sometimes the worm blocks the Ampulla of Vater or
goes into the main pancreatic duct resulting in acute
pancreatitis with raised serum levels of amylase and
lipase.
 Allergies:
 Ascariasis may result in allergies to shrimp and
dustmites due to the shared antigen, tropomyosin;
this has not been confirmed in the laboratory

 Malnutrition:
 The worms in the intestine may cause malabsorption
and anorexia which contribute to malnutrition.The
malabsorption may be due to a loss of brush border
enzymes, erosion and flattening of the villi, and
inflammation of the lamina propria.
 Others:
 Ascaris have an aversion to some general anesthetics
and may exit the body, sometimes through the mouth.

 Taeniasis/cysticercosis:
 Taeniasis is generally asymptomatic.
 It is not fatal, although cysticercosis can cause epilepsy and
neurocysticercosis can be fatal.]Heavy infection is indicated by intestinal
irritation, anaemia, and indigestion.
 The eggs enter the intestine where they develop into larvae. The larvae
enter bloodstream and invade host tissues. This clinical condition, called
cysticercosis, is the most frequent and severe disease caused by any
tapeworm.
 It can lead to severe headaches, dizziness, occasional seizures, dementia,
hypertension, lesions in the brain, blindness, tumor-like growths, and low
eosinophil levels. It is the cause of major neurological problems, such as
hydrocephalus, paraplegy, meningitis, convulsions, and even death.
 It can cause antigen reaction that induce allergic reaction.It is an also rare
cause of ileus, pancreatitis, cholecystitis, and cholangitis.

 Echinococcosis:
 In the patients who are infected with E. granulosus and therefore have cystic
echinococcosis, the disease develops into slow-growing mass in the body.
 These slow-growing masses, are called cysts.these cyst are also common in patients
that are infected with alveolar and polycystic echinococcosis. The cysts found in
those with cystic echinococcosis are usually filled with a clear fluid called hydatid
fluid, are spherical, and typically consist of one compartment and are usually only
found in one area of the body
 If the patient is symptomatic, the symptoms will depend largely on where the cysts
are located. For instance, if the patient has cysts in the lungs and is symptomatic,
they will have a cough, shortness of breath and/or pain in the chest.
 On the other hand, if the patient has cysts in the liver and is symptomatic, they will
suffer from abdominal pain, abnormal abdominal tenderness, hepatomegaly with an
abdominal mass, jaundice, fever and/or anaphylactic reaction.
 Some of the other symptoms includes: Bloody sputum, cough, severe skin
itching.

PREVENTION AND TREATMENT Schistosomiasis:
 Prevention:
 Prevention is best accomplished by eliminating the water-dwelling snails
that are the natural reservoir of the disease.
 Avoiding swimming or wading in freshwater when you are in countries in
which schistosomiasis occurs. Swimming in the ocean and in chlorinated
swimming pools is safe.
 Drinking safe water. Although schistosomiasis is not transmitted by
swallowing contaminated water, if your mouth or lips come in contact with
water containing the parasites, you could become infected.
 Water used for bathing should be brought to a rolling boil for 1 minute to
kill any cercariae, and then cooled before bathing to avoid scalding. Water
held in a storage tank for at least 1 - 2 days should be safe for bathing.

 Treatment:
 Schistosomiasis is treatable by taking by mouth a single
dose of the drug praziquantel annually.
 Other possible treatments include a combination of
praziquantel with metrifonate, artesunate, or mefloquine
 Another agent, mefloquine, which has previously been
used to treat and prevent malaria, was recognised in 2008–
2009 to be effective against schistosoma

 Filariasis:
 Prevention:
 Avoidance of mosquito bites through personal protection
measures or community-level vector control is the best
option to prevent lymphatic filariasis.
 Periodic examination of blood for infection and initiation
of recommended treatment are also likely to prevent
clinical manifestations.
 To eliminate lymphatic filariasis (LF) as a public health
problem we must stop the spread of infection. Levels of
worm larvae (microfilaria) in the blood of infected persons
must be reduced so that mosquitoes cannot transmit the
worms from one human to another.


 Treatmennt:
 The strategy for interrupting transmission is an annual single
co-administration of two drugs for at least five years. The two
alternative regimens are: single doses of albendazole (400mg)
plus Mectizan® (150-200 mg/kg/body wt) or single doses of
albendazole (400mg) plus DEC (6mg/kg/body wt).
 DEC, developed over 50 years ago, is an inexpensive and effective
anti-filarial drug which is used to treat LF in many countries.
DEC is available in tablet form and in a fortified salt formulation
for daily intake at meal times.
 Mectizan® (generic name: ivermectin) is an oral anti-parasitic
drug, discovered and developed by Merck & Co. Inc. which is
effective against both LF and onchocerciasis. Mectizan® is
provided free of charge by Merck & Co. Inc. for the treatment of
onchocerciasis in all endemic countries and for LF in African
countries where onchocerciasis and LF co-exist.
 Albendazole, donated by GlaxoSmithKline for LF prevention, is a
well-established anti-parasitic treatment, given to an estimated
500-800 million people, mostly children, for intestinal infections
over the past 20 years.

 Ascariasis:
 Prevention:
 The best way to prevent ascariasis is to always:
 Avoid ingesting soil that may be contaminated with human
feces, including where human fecal matter ("night soil") or
wastewater is used to fertilize crops.
 Washing hands with soap and warm water before handling food.
 Wash, peel, or cook all raw vegetables and fruits before eating,
particularly those that have been grown in soil that has been
fertilized with manure.
 By-Not defecating outdoors,effective sewage disposal systems
 In areas where more than 20% of the population is affected
treating everyone is recommended. This has a cost of about 2 to 3
cents per person per treatment. This is known as mass drug
administration and is often carried out among school-age
children.

 Treatment:
 Albendazole 400 mg one dose orally is the drug of choice. Ascariasis commonly
coexists with whipworm infection, which appears to be more susceptible to
albendazole than to mebendazole. Albendazole is not recommended during
pregnancy; pyrantel pamoate is the drug of choice in these cases.
 Alternative therapy is mebendazole (100 mg bid for 3 d or 500 mg as a single
dose). Mebendazole is not recommended during pregnancy; pyrantel pamoate
is the drug of choice in these cases.
 Paralyzing vermifuges (eg, pyrantel pamoate, piperazine, ivermectin) should
be avoided in patients with complete or partial intestinal obstruction since the
paralyzed worms may necessitate or further complicate surgery.
 Vitamin A supplementation improved growth development of children in
Zaire; de worming did not improve growth development in this study.
 Drug therapy affects only adult worms. If the patient lives in an endemic area
or has recently relocated, he or she may still be carrying larvae that are not yet
susceptible. Such patients should be re-evaluated in 3 months and retreated if
stool ova persist. In endemic areas, reinfection rates approach 80% within 6
months.
 Nitazoxanide, a drug used primarily for protozoal infection, was shown to have
89% clinical efficacy for the treatment of ascariasis in rural Mexico and may
offer a future alternative to other medications

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