Parasitology

• Medical parasitology: “the study and medical implications of parasites that infect humans”

• A parasite: A living organism dependent on another living organism for its survival in the form of nutrition as well as shelter. Parasites may be simple unicellular protozoa or complex multicellular metazoa

• Eukaryote: a cell with a well-defined chromosome in a membrane-bound nucleus. All parasitic organisms are eukaryotes

• An endoparasite: “a parasite that lives within another living organism” – e.g. malaria, Giardia

• An ectoparasite: “a parasite that lives on the external surface of another living organism” – e.g. lice, ticks

Parasites are found in all groups of organisms

Hosts and life cycles Host: “the organism in, or on, which the parasite lives and causes harm

• The definitive host is by definition the one in which the parasite reproduces sexually

• intermediate hosts the organism in which the parasite lives during a period of its development only”

• Host which actively transmit parasites to humans are often called vectors

• In paratenic or transport hosts no parasite development occurs

• Reservoir host are alternate animal host from which the parasite can be transmitted to humans (zoonosis) or domestic animals

• Accidental host, not suitable for parasite development, but can cause disease

Disease terminology • Prepatency: infected but parasite presence can not be detected yet

• Patency: established infection, parasite stages can be detected (malaria parasites in blood smears, worm eggs in feces etc.)

• Incubation period: time between infection and the development of symptoms

• Acute disease can lead to crisis which can resolve in spontaneous healing, chronic infection or death

• Convalescence: Period after healing, absence of infectious agents, no symptoms, in certain case immunity to reinfection

Epidemiology

• Although parasitic infections occur globally, the majority occur in tropical regions, where there is poverty, poor sanitation and personal hygiene

• Often entire communities may be infected with multiple, different organisms which remain untreated because treatment is neither accessible nor affordable

• Effective prevention and control requires "mass intervention strategies” and intense community education. Examples include:

• General improved sanitation: pit latrines, fresh water wells, piped water

• Vector control: insecticide, impregnated bed nets, spraying of houses with residual insecticides, drainage, landfill

• drug administration programmes which may need to be repeated at regular intervals

CLASSIFICATION

• Protozoa are further divided into:

1. Sarcodina (amebas)

2. Sporozoa (sporozoans)

3. Mastigophora (flagellates)

4. Ciliata (ciliates)

PROTOZOA

PROTOZOA

• Single-celled Eukaryotes

• Free-living or parasitic

• 2 forms:

1. Cyst form (infective for humans) &

2. Trophozoite form

• Protozoa are grouped as :

1. Intestinal protozoa

2. Urogenital protozoa

3. Blood and tissue protozoa

1. Intestinal protozoa

i. Entamoeba histolytica (ameba)

ii. Giardia lamblia (flagellate)

iii. Cryptosporidium parvum (sporozoan)

2. Urogenital Protozoa:

i. Trichomonas vaginalis (flagellate)

3. Blood & Tissue Protozoa:

i. Leishmania species (flagellate)

ii. Trypanosoma species (flagellate)

iii. Toxoplasma gondii (sporozoa)

iv. Plasmodium species (sporozoa)

ENTAMOEBA HISTOLYTICA

• Occurs worldwide,

• endemic in tropics & subtropics

• ROUTE OF TRANSMISSION:

– fecal-oral route

BY contaminated food & water

• Sources of infection – carriers (asymptomatic & convalescent), houseflies, cockroaches

• Risks – poverty, lack of hygiene, poor sanitation, mental retardation, male homosexuals

Protozoan

DISEASES:

• E. histolytica causes:

1. Asymptomatic infection (90%)

2. Acute intestinal amebiasis (Amebic Dysentery)

3. Chronic amebiasis

4. Amebic liver abscess

5. Infrequently abscess in brain, lungs & other organs

Clinical presentation

• 1. Acute intestinal amebiasis: dysentry, lower abdominal discomfort, tenesmus, & flatulence.

• 2. Chronic amebiasis

• 3. Amebic abscess: if in liver, cause right upper quadrant pain, weight loss, fever & a tender, enlarged liver.

Balantidium coli: a large motile ciliated parasite that lives in the colon of pigs, humans and rodents and can lead to colonic ulceration

Giardia intestinalis (G. lamblia; G. duodenalis)

• Giardiasis.

• Worldwide in distribution

- Found in duodenum and upper part of jejunum

• Has both trophozoite and cyst stage.

Giardia intestinalis Trophozoite

Trophozoites are binucleated

(looks like a face)

14-7μm.

The shape is like that of a tennis

or badminton racket when viewed

flat, and

like a longitudinally split pear

when viewed side to side.

Cyst of Giardia intestinalis

Morphology:

• Oval in shape; 8-12 µm long x 7-10 µm wide.

• Thin cyst wall.

• 4 nuclei, may remain clustered at one end or

lie in pairs at opposite poles.

• Remains of flagella and margins of sucking

disc may be seen inside the cytoplasm.

Detected in the blood

• Trypanosoma: haemoflagellates which cause • In Africa - sleeping

sickness (transmitted by the Tsetse fly)

• In South America - Chagas disease (transmitted by the Reduviid bug)

Tsetse fly

– the vector of African

trypanosomiasis

It has a painful bite!

Trypanosoma Flagellates (Protozoan)

Chagas diseases occurs in 15 Central

and South American countries.

The symptoms of Chagas disease vary

over the course of an infection. In the

early, acute stage, symptoms are mild

and usually produce no more than

local swelling at the site of infection.

As the disease progresses, over the

course of many years, serious chronic

symptoms can appear, such as heart

disease and malformation of the

intestines. If untreated, the chronic

disease is often fatal.

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Malaria is a major public health problem in warm climates especially in developing countries.

It is a leading cause of disease and death among children under five years, pregnant women and non-immune travellers/immigrants.

Malaria

MALARIA

• Name means “bad air”-

• A life-threatening parasitic disease

• 40% of the world’s population is at risk

• 90% of the deaths due to Malaria occur in Sub-Sahara Africa, mostly among young children.

• Around 400-900 million people are affected

• At least 2.7 million deaths annually.

What is malaria ?

Malaria is a disease caused by the protozoan parasites

of the genus Plasmodium. The 4 species that commonly

infect man are: Consists of 4 species:

P. vivax

P. falciparum

P. malariae

P. ovale

• Plasmodium parasites are highly specific with female

Anopheles mosquitoes

Benign tertian malaria = Vivax Malaria

Malignant tertian Malaria = Falciparum Malaria

Quartian Malaria = P. malaria

Ovale malaria -P. ovale

Incubation period

• P. vivax (in T)urkey

• P. ovale 10 to 14 days

• P. falciparum

• P. malariae 18 days to 6

weeks

Falciparum Malaria

• Most widespread

• Accounts for 80% of malaria cases worldwide

• Most pathogenic of human malaria species

• Untreated infections - severe disease & even death,

particularly in young children, pregnant woman &

non immune adults.

Clinical Features

• Series of febrile paroxysms

• Quartan malaria – every 72 hrs

Tertian malaria - every 48 hrs

* each paroxysm has 3 stages - cold stage (rigors), hot stage (high temp., body & joint pains, vomiting & diarrhoea) and perspiration stage (fall in temp.)

Malaria Prevention Mosquito avoidance - evening and night behavior

- mosquito nets

- air conditioning

- screens

- mosquito repellants

- pyrethrin coils

Mosquito killing - destroying breeding sites

- fog spraying

- residual spraying

Plasmodium killing - chemoprophylaxis

Leishmaniasis

• Leishmaniasis is a widespread and complex disease that exhibits several forms

• Leishmaniasis is transmitted by the bite of a sand fly

-These insects are smaller than mosquitoes

-They can actually fit through the mesh of standard netting

-The infective form is in the saliva of the insect

• Leishmaniasis protozoan pathogens are of about 20 different species and can be categorized into 3 groups:

- Leishmania Donovani (L. visceralis in Tr)

- Leishmania Tropica (L. cutaneous inTr

- Leishmania Braziliensis

L. Donovani (Visceral Leishmaniasis)

• This protozoa multiplies in the liver and spleen, causing organs to enlarge greatly.

• Eventually, kidney function is also lost as these organs are invaded.

• Leishmaniasis is often fatal and without proper treatment can result into death within 1-2 years

L. Tropica (Cutaneous Leishmaniasis)

• Leishmania Tropica is a cutaneous form of leishmaniasis and is sometimes called the orienatal sore.

• A papule appears at the bite site after a few weeks of incubation.

• The papule ulcerates and, after healing, leaves a prominent scar

Cutaneous Leishmaniasis • Most common form

• Characterized by one or more sores, papules or nodules on the skin

• Sores can change in size and appearance over time

• Often described as looking somewhat like a volcano with a raised edge and central crater

• Sores are usually painless but can become painful if secondarily infected

• Swollen lymph nodes may be present near the sores (under the arm if the sores are on the arm or hand…)

Leishmania Braziliensis

• Also known as Mucocutaneous Leishmaniasis

• Mostly found in Yucatan Peninsula of Mexico and rainforests areas of central and South America.

•Affects mucous membrane as well as skin.

Causes disfiguring destruction of tissues of

the nose, mouth, and upper throat.

Prevention

• Suppress the reservoir: dogs, rats, gerbils, other small mammals and rodents

• Suppress the vector: Sandfly

• Critical to preventing disease in stationary troop populations

• Prevent sandfly bites: Personal Protective Measures

• Most important at night

• Sleeves down

• Insect repellent

• Permethrin treated uniforms

• Permethrin treated bed nets

Introduction:

• Toxoplasmosis infection is caused by a parasite called Toxoplasma gondii.

• Toxoplasma gondii was first discovered in 1908.

• Toxoplasma gondii is a intracellular parasite in intestinal epithelium and muscle.

• It can be found free in the blood and peritoneal exudate.

EPIDEMIOLOGY / TRANSMISSION

• Toxoplasmosis is one of the most common infections of humans throughout the world(30 – 50% of global population exposed or chronically infected)

• Infection is more common in warm climates and lower altitudes than cold climates and mountainous regions.

• Distribution is probably related to conditions favoring the sporulation and survival of oocysts.

Enteric cycle or sexual cycle

Exo enteric cycle or asexual cycle

Life cycle – two phases:

Primary Transmission of Toxoplasmosis

• Ingesting cysts

• Raw or undercooked meat

• Especially pork, mutton

• Ingesting oocysts

• Accidental ingestion of feline feces

• Contaminated dirt at playgrounds or sandboxes

• Hands contaminated when changing litter boxes

Ways of Infection Oral intake of raw or rare ("under-

cooked") meat or of contamination with cats feces or consumption of contaminated vegetables, fruits, and salad, ...

• A fresh maternal infection during pregnancy can lead to an infection of the placenta.

• Congenital Toxoplasmosis results from transplacental infection of the fetus during pregnancy.

•

Transmission Cycle DEFINITIVE HOST (cat)

Cysts ingested

by cat

Unsporulated oocyst

passed in feces

Sporulated

oocyst

Intermediate host

ingests oocysts in

feed, water, or soil

Cysts containing bradyzoites

in tissues of intermediate hosts

INTERMEDIATE HOSTS

Contamination of

food and water

Ingests cysts

in infected meat

Infection of fetus

Tachyzoites

transmitted

through placenta

life-cycle for Toxoplasma gondii

• The asexual stages of T. gondii can cause disease

in humans and most animals .

• There are two asexual forms. The first form, called

• tachyzoite,( fast replicating form) can invade all types of cells and divides rapidly, leading to cell death .

• The second form, called the bradyzoite, divides

• slowly and forms cysts, most prominently in

• muscle and brain. Tissue cysts can be ingested by a cat where they undergo sexual reproduction and oocyst formation.

Congenital Toxoplasmosis

A)Frist

trimester…… Abortion B)Second

trimester…Stillbirth

C)Third trimester…Infection may be present as:-Hydrocephaly,

Neonatal jaundice . Mental retardation.

Congenital Toxoplasmosis

• The consequences of the infection of the fetus can be very different: between subclinical and very serious.

• Abortion Overt disease. The symptoms vary widely, the classical triad of Congenital Toxoplasmosis is Hydrocephalus

• Intracranial calcification

• Chorioretinitis

Toxoplasmosis prevention of Congenital.

• Primary prevention is an information about the ways of infection (cats, raw meet) to avoid ingestion or inhalation. This is important for all pregnant women who are "seronegative"

• Secondary prevention is the detection of infected women during pregnancy to start treatment before the fetus gets infected.

• Tertiary Prevention is the treatment of infected children to reduce or avoid symptoms.

Helmints

Some of them are;

Taenia saginata

Taenia solium

Trichinella spiralis

Ascaris lumbricoides

Diphylobotrium latum

Fasciola hepatica

Trichuris trichura

Taenia saginata

• Also called beef tapeworm

• Word wide, highest prevalence (up to 27%) are in central Asia, the Near East, and Central and East Africa.

• Habitat: upper jejunum of man

• Definitive host : human

• Intermediate host : cattle's

T. saginata

Scolex

T. saginata T. solium

Egg of T. saginata and T. solium

Pathogenesis

• Adult tapeworms : minimal local pathology

• Vague abdominal discomfort, indigestion, diarrhoea, constipation, loss of appetite

• An immune response to adult tapeworms provokes eosinophilia and immunoglobulin E(IgE) elevation in some patients

Taenia solium

• Also called pork tapeworm

• T. solium infection is endemic include Mexico, Central America, South America, Africa, Southeast Asia, India, the Philippines, and southern Europe.

• definitive host : human

• Intermediate host : pigs or human

Taenia solium

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ECHINOCOCCUS

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Echinococcus spp.,

• Echinococcus granulosus

• Dog tapeworm

• Echinococcosis

• Liver, lung, kidney

and brain of Humans

and cows

Habitat: Small intestine (Harbour only larval form but not adult form)

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Echinococcus spp.,

• Definitive host: Dog, wolf, fox, jackal

• Intermediate host: Sheep, pig, cattle, goat and man

• Larval form of e. granulosus causes Hydatid disease

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Hydatid cyst

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Echinococcus granulosus Hydatid disease

• The cystic form is hydatid disease

• Final host is dog and other caniids

• Intermediate hosts are cattle, ruminants, pigs,

• Man is an accidental intermediate host

• The eggs are released from the dogs into the ground where they are picked

• The larvae go through the walls of small intestines and finally into the liver, lungs, peritoneal space, even in the brain.

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Signs

• Signs depend upon the site of infection

• Liver cysts cause abdominal pain or a palpable mass. Jaundice may occur if the bile duct is obstructed. Rupture into the bile duct, peritoneal cavity, or lung may cause fever, urticaria, or a serious anaphylactic reaction.

• Pulmonary cysts can cause cough, chest pain, and hemoptysis.

• Brain and spinal cord; cause epilepsy and blindness

TRICHINELOSIS • Etiology

• Trichinella spiralis, T. nativa, and T. britovi

• Hosts • All mammals, principally, pigs, man, rats, etc

• Life cycle. Clean life cycle. It has no free living stages outside the host.

• After ingestion, it gets encysted in the muscles

• Larvae get released from muscles by action of digestive enzymes.

• Larvae enters the lymphatic system to the circulating system finally back to muscles

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Trichinella spiralis

Trichinella spiralis

Common name: Trichina worm- The Pork worm

Trichinella spiralis means spira, how this coils up in its host.

diseases: Trichinosis, Trichiniasis,

is a zoonotic disease. it is passed between humans and animals.

Habitat: females in mucosa of small intestinal

The same animal acts as final and intermediated host

is most common in Europe, North America, and Asia,

Infective stage: contaminated meat (muscle) containing encyst larvae (pig)

Diagnostic stage: larvae encysted in muscle (human)

Can be fatal if large numbers of cysts form in the heart muscle.

Epidemiology

The disease among humans, rats, and pigs

Rats and pigs feeding on garbage that includes

infected pork waste, become infected in turn

Dead or dying infected rats are themselves eaten

by pigs

Raw or poorly cooked pork (sausage) harboring

infective larvae then becomes the vehicle for human

infections

Trichinellosis is a cosmopolitan disease that

occurs most commonly in Europe and the US

Prevention • The best way to prevent trichinellosis is to cook meat

to safe temperatures.

• For Whole Cuts of Meat (excluding poultry and wild game)

• Cook to at least (63° C).

• For Ground Meat (excluding poultry and wild game)

• Cook to at least (71° C);

(CDC, 2012)

Enterobius vermicularis (Pin worm)

causes ENTEROBIASIS.

Distribution: worldwide

Morphology: Adult female worms are up to

10mm in length, and male worms are up to 5

mm.

Location: the lower part of small intestine, the

upper part of large intestine.

Eggs are transparent and colourless,

asymmetrical, with thin and smooth membrane,

40-60 µm.

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Enterobius vermicularis Clinical manifestation: Infection is frequent among children under

12 years of age.

- perianal itching is most common symptom;

- vaginal irritation caused by the female migration;

- the itching results in insomnia and restlessness;

- in some cases gastrointestinal symptoms (pain, nausea, vomiting, etc.) may develop.

Laboratory diagnosis:

1) the eggs are recovered from perianal skin by using the “Scotch tape” technique and can be observed microscopically;

2) anal swabs (a paddle coated with adhesive material).

3) seldom adult worms and eggs can be found in the stool.

4) microscopic examination of nail beds

Prevention: personal hygiene, keep sanitary condition, treatment of patients

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Ascaris lumbricoides causes : Ascariasis

Distribution: worldwide.

more than 1.4 billion people are infected

with Ascaris lumbricoides, representing

about 25 % of the world population (WHO).

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Ascaris lumbricoides Clinical manifestation:

- In pulmonary stage: larvae may lead to brief period of cough, wheezing, dyspnoea and substernal discomfort, eosinophilia. Also it can cause pneumonia, bronchial asthma.

- In intestinal stage: adults cause weakness, weight loss, anorexia, intermittent loose stool and intestinal obstruction, penetration of the intestinal wall, occlusion of the bile duct, the pancreatic duct or the appendix, toxic effects (nausea, vomiting). Most infections are asymptomatic.

Prevention:

washing hands before meals;

proper washing of vegetables eaten raw;

treatment of patients;

proper disposal of faeces;

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