Liwei Li

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Human Parasitology(??????)

• Liwei Li
• Department of Medical Microbiology and
  Parasitology
• College of Medicine, Zhejiang University
• lilw2_at_zju.edu.cn

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Introduction to Parasitology

• F. E. G. Cox. History of Human Parasitology.
  Clin Microbiol Rev. 2002 October 15 (4) 595612
  http//www.pubmedcentral.nih.gov/articlerender.fcg
  i?artid126866
• Olson Guselle. Are pig parasite a human health
  risk? http//www.banffpork.ca/proc/2000pdf/Chap13-
  Olson.pdf

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You need to know in the course of human
parasitology

• What is parasitology?
• What are parasitism, parasite and host ?
• What is the life cycle of a parasite?
• How is the host-parasite interplay ?
• How do we diagnose the infections with parasites?
• What do we need to understand in the epidemiology
  of parasitic infections?
• What are principles of control of parasitic
  diseases?

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Pathogens

microbes
parasites
protozoa helminthes arthropods
bacteria viruses fungi
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Pathogens Infectious or communicable diseases!
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Definition of Parasitology

• Parasitology is a discipline dealing with the
  biology of animal parasites, ecology of
  parasitism with emphasis on parasite--host and
  parasite--environmental interactions.
• Human parasitology or Medical parasitology is
  restricted in studying those parasites that are
  of importance in medicine
• Protozoology, helminthology and entomology
• Parasitology is usually in the scope of
  preventive
• medicine and the foundation of clinical
  parasitic diseases

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Subject outline

• In this course we will concentrate on 3 major
  groups of parasites
• 1. Medical protozoa - flagellates, amoebae,
  malarial organisms
• 2. Medical Helminthes - parasitic worms such as
  the flukes, tapeworms, and roundworms
• 3. Medical Arthropods - insects and arachnids
  that are ectoparasites and carriers (vectors) of
  diseases

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Why do we study parasitology?

• Parasites provide unique examples of biological
  phenomena not found in free-living organisms
• _
• Medical importance
• Veterinary importance
• Economic importance

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Medical Importance of Parasites

• Humans are hosts to over 100 species of
  parasites.
• Many of these parasites are causative agents of
  major public health problems of the world.

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Medical Importance of Parasites

• Ten major tropical diseases (UNDP/World
  bank/TDR, 2000)
• Malaria(??)
• Shistosomaiasis(????)
• Filariasis (???,Lymphatic filariasis and
  Onchocerciasis)
• Leishmaniasis(????)
• Trypanosomiasis (???,African trypanosomiasis and
  chagas disease )
• Leprosy(???)
• Tuberculosis (???)
• Dengue fever (???)

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Major human parasites

• Estimated World Prevalence of the Major Parasitic
  Infection of Human
• Malaria
  300-500 million
• Schistosomiasis
  200 million
• Lymphatic filariasis
  120 million
• Onchocerciasis
  85 million
• Leishmaniasis
  12 million
• Trypanosoma cruzi (South America)
  18 million
• Ascaris infection
  1300 million
• Hookworm infection
  1300 million
• Amoebiasis
  60 million
• Trichuriasis
  900 million
• Gardiasis
  200 million

(WHO,1999)
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Examples of Medical Importance in the World
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Medical Importance in China

• Five major parasitic diseases
• Malaria
• Schistosomiasis
• Kala-azar (???)
• Filariasis
• Hookworm disease

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Medical Importance in China
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Medical Importance in China
Parasite infection Estimated number of cases(2004)
Malaria (P.v P.f infection) 60.2 thousand (2006)
Ascariasis (large roundworm infection) 85.9 million
Trichuriasis (whipworm infection) 29.1million
Hookworm disease(A. d and N. a infection) 39.3 million
Clonorchiasis (oriental liver fluke infection) 12.5 million
Fasciolopiasis (intestinal fluke infection) 2 million
Paragonimiasis(lung fluke infection) 2.95 million
Taeniasis (pork and beef tapeworm infection) 1.5 million
Schistosomiasis (blood fluke infection)   843 thousand (2003)
Chinas parasite infection based on the
nationwide parasite survey
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Medical Importance in China

• Food-borne parasitic disease is still a big
  problem.
• Prevalence of pet-borne parasitic disease has
  increased.
• Prevalence of opportunistic parasitic disease has
  increased.
• Material exchange and population migration has
  widened the geographical scope of parasitic
  disease.
• Medical professionals generally lack the
  knowledge of parasitology.

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WHAT TYPES OF LIVING ORGANISMS ARE PARASITIC?
Parasites occur in two of the five kingdoms of
living organisms. What are the 5 kingdoms?
 
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KINGDOM PROTISTA - contains the single-celled
protozoans.
KINGDOM ANIMALIA contains 32 phyla.

• Parasites of importance are concentrated in 3
  phyla.
• PHYLUM PLATYHELMINTHES Class Trematoda
  Cestoda
• PHYLUM NEMATODA Class Nematoda
• PHYLUM ARTHROPODA Class Insecta

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What are parasitism, parasite and host?

• Evolution of parasitism
• Understanding start with basic concept of
  symbiosis
• Symbiosis was first coined by the German de Bary
  in 1879 - to mean living together. It was
  originally coined to refer to all cases where
  dissimilar organisms or species (e.g.,
  heterogenetic associations) live together in an
  intimate association

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• Interactions of Symbionts
• In order to facilitate our understanding of
  symbiosis, 3 subordinate categories of symbiotic
  relationships are indicated. They are
  commensalism (including phoresis), mutualism, and
  parasitism

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Symbiosis (cont.)

• 1. Mutualism(????)
• This occurs when each member of the association
  benefits the other
• The mutuals are metabolically dependent on one
  another. Sometimes, one cannot survive in the
  absence of the other
• eg. the flagellate cannot
• survive outside the termite

Sea anemones and anemonefish
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Symbiosis (cont.)

• 2. Commensalism(????,??)
• Commensalism means eating at the same table and
  in many commensalistic relationships one organism
  (the commensal) is feeding on food that was not
  consumed by the host
• Commensalism occurs when one member of the
  associating pair, usually the smaller, receives
  all the benefit and the other member is neither
  benefited nor harmed
• To carry -- phoresis
• Example Remora fish associated with sharks
  feeds on leftover food

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Symbiosis (cont.)

• 3. Parasitism(??)
• A parasitos (para beside sitos grain or food)
  Original meaning from the Greek is a relationship
  in which "one eats at another's table or lives at
  another's expense."
• Parasitism is a relationship in which one of the
  participants, the parasite, either harms its host
  (the part that got harmed) or in some sense lives
  at the expense of the host.
• Debate The amoeba Entamoeba invadens is
  harmless in turtles but causes 100 mortality in
  snakes.
• Is it then a commensal (when its in
  turtles) or is it a parasite (when its in
  snakes)?
• The true nature of parasitism involves an
  ecological relationship between the parasite and
  its host. A parasite is metabolically dependent
  on its host.

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Symbiosis (sum.)

• The categories of symbiosis are man-made
  constructs introduced primarily for convenience
  (they allow us to categorize natural symbiosis
  associations). There can in fact be overlap
  between various categories.

Overlap between the major categories of symbiosis
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Parasite In the relationship known as
parasitism, the partner lives in or on another
from which it gains benefit, always smaller, is
the parasite which to some degree injures its
partner. Parasites (animal parasites) are
invertebrates that can not live independently and
should depend upon others to maintain their lives
(live at the expense of others).
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• Parasites may be classified according to
  different ways
• residing site---endoparasite / ectoparasite
• ecology---obligatory/facultative accidental
  or
• opportunistic
• duration of parasitism---permanent/intermitten
  t

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Kinds of Parasites

• An organism that does not absolutely depend on
  the parasitic way of life, but is capable of
  adapting to it if placed in such a relationship
  is known as a facultative parasite
• If an organism is completely dependent on the
  host during a segment or all of its life cycle
  the parasite is known as an obligatory parasite
• Parasites that live within the body of their host
  (intestinal tract, liver, etc.) are called
  endoparasites
• Parasites that are attached to the outer surfaces
  of their hosts are called ectoparasites

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Host

• Definition In the parasitism, the partners
  which provide the food and shelter for parasites,
  and to some degree are injured by this
  association, are scientifically called as hosts.
• larger, more complex and better regulated
  bodies

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Types of the host

• A definitive host(???) is the host in which the
  parasite become sexually mature (where the adult
  worm harbor or undergoing sexual reproduction).
• An intermediate host(????) is host in which the
  parasite undergoes larval development but does
  not reach sexual maturity, parasites often can
  undergo asexual reproduction in this type of
  host.

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Definitions of Hosts (cont.)
Reservoir host(????) is referred to those animals
that harbor an infection that can be transmitted
to humans. Even if the animal is the normal host
of the parasite, it is the reservoir for the
zoonotic infection of people.Thus,the reservoir
host shares the same stage of the parasite with
humans.
Zoonosis(?????) a disease of animals that may be
transmitted to humans under natural conditions.

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Definitions of Hosts (cont.)
A transport/paratenic/transfer host (????) When
parasite enters the body of an abnormal host and
not undergoes any development but continues to
stay alive and be infective to the normal
host.The host is called the transport host. not
necessary for the completion of the parasites
life cycle
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Definitions of Hosts (cont.)

• Immune compromised hosts are persons who are
  considered to have reduced resistance to illness
  include  infants, hospital patients, pregnant
  women, frail, elderly people, malnourished
  individuals, people with controlled physical or
  metabolic disorders (e.g., diabetes or high blood
  pressure), people with AIDS.

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Definitions of Hosts (cont.)

• Opportunistic parasitic infection Any infection
  caused by a parasite that does not normally cause
  disease in humans occurs in persons with
  abnormally functioning immune systems (as AIDS
  patients or transplant patients receiving
  immunosuppressive drugs).
• For example Toxoplasma gondii, Crypsosporidium
• (Pneumocystis
  jeroveci (carinii) -----
• Pneumocystis
  pneumonia, PCP)

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Definitions of Hosts (cont.)
Vector parasite infections may be carried from
one host to another by means of arthropod
vectors. A vector may also be a host if
development of the parasite takes place with its
body.(If the arthropod is simply an instrument of
passive transfer, we refer to it as a mechanical
vector)
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What is the Life Cycle

• Life cycle described the ontogenesis, development
  and reproduction of the parasite, tracking it
  through the various phases of its life history
  which will encompass both parasitic and
  non-parasitic stages.

The key to understanding the transmission of a
parasite species and parasitic disease is its
life-cycle
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Generalized stages of a parasites life
cycle Stage in human host (linking to
pathogenesis) Stage to discharge (diagnostic
stage) Stage developing outside human host (
in external environment, intermediate host or
insect host)--- (linking to transmission) Stage
infecting men (infective stage)
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Parasite Life CycleA generalized mode
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The types of life cycle of parasites Direct
type one host (definitive host)
---geo-helminth Indirect type more one
hosts(intermediate host(s)
and definitive host) ---bio-helminth
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Life cycle (cont.)

• Simple or Direct Life Cycle (monoxenous) is one
  in which there is only one host where the
  parasite often spends most of its life, usually
  as an adult, and where it reproduces.

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Life cycle (cont.)

• Many parasites have more complex cycles which
  include 2 or more hosts and are classified as
  having indirect life cycles.

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host-parasite interactions

• Adaptations to parasitism
• Profound morphological adaptation to their way
  of life
• Organs not necessary to a parasitic existence
  are
• frequently lost or degenerated
• Reproductive system is very highly developed in
• association with increased reproductive
  capacity      
• Specialized attachment organs in the form of
  suckers
• and hooks have been developed  
• Physiological and biochemical adaptations
• Immune evasion

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The harmful effects on the host
host-parasite interactions

• Depriving for nutrition
• Mechanical damage
• Toxic effects
• Immune-pathological consequences

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Ascaris in small intestine
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Hookworm and anemia
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Complete blockage of intestine caused by Ascaris
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Allergy caused by mosquito bites
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schistosomiasis
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host-parasite interactions

• Effects of the host to the parasite
• Genetic constitution of the host may profoundly
  influence the host-parasite relationship (racial
  variations in resistance to certain strains of
  Plasmodium vivax sickle cell trait increased
  resistance to infection with P. falciparum )

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host-parasite interactions

• Effects of the host to the parasite
• Anti-parasitic immune responses 
• Natural immunity mucocutaneous barrier, blood
  brain
• barrier, phagocyte, complement, defensins
• Acquired immunity
• Sterilizing immunity (cutaneous leishmaniasis)
• Non-sterilizing immunity premunition (????),
  concomitant immunity (????)

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host-parasite interactions

• Colonized (infected), asymptomatic
• Differences in host susceptibility
• Many people are asymptomatically infected with
  Toxoplasma gondii.
• Capable of spreading microbe
• Amoeba carrier
• Colonized, infected, symptomatic
• Infected, host death

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Characteristics of parasitic disease (infection)

• Chronic infection, carrier
• Suppressive infection(????)
• Polyparasitism
• Eosinophilia(????????)
• IgE ?
• Larva migrans(?????)
• Ectopic parasitism(????)

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Diagnosis

• Diagnostic techniques
• Etiological techniques
• Immunodiagnostic techniques
• Other molecular diagnostics

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Epidemiology principles of control

• Basic and essential links for parasitic diseases
• Source of infection patients, carriers,
  reservoir hosts
• Route of infection
• Susceptible population

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Epidemiology principles of control(cont.)

• Endemic factors
• Natural factors
• One wont get parasitic diseases in the polar
  area
• Social factors
• Eating habits, hygienic habit
• Sexual transmitted diseases

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Epidemiology principles of control(cont.)

• Principal of disease control
• Control the source of infection
• Cut off the route of transmission
• Massive protection, esp. for the susceptible
  population
• no successful vaccine

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Epidemiology principles of control(cont.)

• Health Education

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Round Worms
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Introduction

• Among the commonest of all parasites and
  responsible for diseases of major importance in
  humans
• Non-segmented roundworms belonging to the Phylum
  Nemathelminthes, Class Nematoda
• The sexes are usually separate (Dioecious), the
  male which is smaller than the female commonly
  has a curved posterior end

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Morphology

• Cylindrical and slender
• Bilaterally symmetrical
• Sex-differentiated
• Celomic cavity protocoele
• The supporting body wall consists of cuticle
  layer, syncytial layer (subcutical layer) and
  longitudinal muscular layer
• The alimentary tract is a simple tube extending
  from the mouth to the anus

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Morphology

• No circulatory system
• The reproductive system is in tubular form with
  dioecious (sex-differentiation)
• Male testis, vas deferens, seminal vesicle, and
  ejaculatory duct, also cloaca and spicule
• Female ovary, oviduct, seminal receptacle,
  uterus, ovejector and vagina

Digestive system
male reproductive system
female reproductive system
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Physiology

• The methods of obtaining food may be classified
  as
• Sucking with ingestion of blood (Ancylostoma)
• Ingestion of lysed tissues and blood (Trichuris)
• Feeding on the intestinal contents (Ascaris)
• Ingestion of nourishment from the body fluids
  (filarial worms)
• Metabolism mainly aerobic metabolism, and most
  species need free-living periods for larvae,
  which are capable of withstanding a wide range of
  environmental condition
• During larval development, nematodes pass through
  several molts or ecdysis, both inside and outside
  the host

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Life cycle

• Geo-helminths
• Only one host the larvae pass from host to host
  directly or after a free-living existence
• Transmission to a new host depends upon
• the ingestion of the mature infectious eggs with
  larvae (Ascaris, Pinworm)
• the penetration of the skin or mucous membranes
  by the larvae (Hookworm)
• Bio-helminths
• Have an intermediate host
• Transmission to a new definitive host is
  intermediated by the arthropod--- (filarial worm)

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Common medical nematodes species

• Intestinal lumen residing nematodes
• Ascaris, Hookworm, Whip worm, Pinworm----the
  adult parasite inhabit in human intestinal tract
• Blood and tissue residing nematodes
• Filaria, Thichinella----the location of the adult
  parasite is blood or tissue

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Ascaris lumbricoides(?????,??)
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General Introduction

• Common saying round worm of man
• The largest of the intestinal nematodes
  parasitizing humans
• The most common worm found in human
• It is worldwide in distribution and most
  prevalent through out the tropics, sub-tropics
  and more prevalent in the countryside than in the
  city

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Morphology

• Adult
• Cylindrical in shape
• Creamy-white or pinkish in color
• The female averages 20-35cm in length, the
  largest 49cm
• The male is smaller, averaging 15-31cm in length,
  has a typical curled tail with a pair sickle like
  copulatory spines
• On the tip of the head there are three lips,
  arranged as a Chinese word ?
• Male has a single reproductive tubule
• The female has two reproductive tubules and the
  vulva is ventrally located at the posterior part
  of the anterior 1/3 of the body

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Adult worm of A. lumbricoides
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The lips of A. lumbricoides
The three lips are seen at the anterior end.
The margin of each lip is lined with minute teeth
which are not visible at this magnification
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Morphology

• Egg
• There are three kinds of the eggs
• fertilized eggs
• unfertilized eggs
• decorticated eggs
• We usually describe an egg in 5 aspects
• size, color, shape, shell and content

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Morphology

• Fertilized egg
• an average size 6045µm
• broad oval in shape
• brown in color
• The shell is thick
• Albuminous coat is thick and stained brown by
  bile
• The content is a fertilized ovum
• There is a new-moon(crescent) shaped clear space
  at each end inside the shell

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Morphology

• Unfertilized egg
• Longer and slender than fertilized egg
• The shell and albuminous coat are thinner
• than those of the fertilized egg
• The content is made of many refractable
• granules various in size
• Decorticated egg
• Both fertilized and unfertilized eggs sometimes
  may lack their outer albuminous coats and are
  colorless

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Life Cycle
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Life Cycle

• Site of inhabitation small intestine
• Infective stage embryonated eggs
• Route of infection by mouth
• Blood-lung migration intestine--- blood stream
  --- right side of the heart --- lung ---
  respiratory tree --- coughed up and swallowed ---
  small intestine

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Life Cycle

• No intermediate and reservoir hosts
• The time from the ingestion of embryonated eggs
  to oviposition by the females is about 60-75 days
• Life span of the adult about 1 year
• Female may produce approximately 240,000 eggs per
  day, which are passed in feces

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Pathogenesis

• The blood-lung migration phase of the larvae
  During the migration through the lungs, the
  larvae may cause a pneumonia (temporary).
• The symptoms of the pneumonia are low fever,
  cough, blood-tinged sputum, asthma
• The clinical manifestation is also called
  Loefflers syndrome

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Pathogenesis

• 2. The intestinal phase of the adults
• No symptoms to vague abdominal pains or
  intermittent colic, especially in children
• A heavy worm burden can result in malnutrition
• Wandering adults may block the appendical lumen
  or the common bile duct and even perforate the
  intestinal wall which cause complications of
  ascariasis
• intestinal obstruction
• Appendicitis
• biliary ascariasis (the most common one)
• perforation of the intestine
• cholecystitis, pancreatitis and peritonitis

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Diagnosis

• The symptoms and signs are for reference only
• Intestinal ascariasis feces are examined for
  the ascaris eggs
• Direct fecal film it is simple and effective and
  is the first choice
• brine-floatation method
• recovery of adult worms when adults or
  adolescents are found in feces or vomit and
  tissues
• Ascaris pneumonitis examination of sputum for
  Ascaris larvae is sometimes

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Epidemiology

• Worldwide distribution, very common in China,
  especially in the countryside.
• Infection rate
• rural gturban
• children gt adults

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• Factors favoring the spread of the transmission
• Simple life cycle
• Enormous egg production ( 240,000 eggs/ day/
  female )
• Eggs are highly resistant to ordinary
  disinfectants ( due to the ascroside) which may
  remain viable for several years
• Social customs and living habits.
• Disposal of feces is unsuitable

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Prevention

• Treatment to ascariasis Mebendazole(????)
  Albendazole(????)
• Sanitary disposal of feces.
• Hygienic habits such as cleaning of hands before
  meals.
• Health education.

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Hookworms (??)

• Two major species of hookworms
• can infect human
• Necator americanus
• (??????)
• Ancylostoma duodenale
• (????????)

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General Introduction

• Human intestinal nematode of smaller size,
  inhabits the small intestine
• World-wide distribution, about 900 million
  infections in the world
• A. duodenale is prevalent in Southern Europe,
  North Africa, Northern Asia (North China), and
  the more pathogenic one
• N. americanus is the predominant species in the
  Western hemisphere and equatorial Africa (South
  China)
• Many areas are endemic for both species
• Heavy infection may evoke anemia known as "Yellow
  Laziness"

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Morphology Adults

• Ancylostoma duodenale
• Female is 10-13 mm in length by 0.6 mm in
  diameter
• Males are 8-11 mm by 0.4 mm
• Posterior end has an umbrella-shaped bursa with
  riblike rays
• Two pairs of curved teeth on the ventral wall of
  its buccal capsule

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Morphology Adults

• Necator americanus
• Females are 9-11 mm in length by 0.4 mm in
  diameter
• Males are 7-9 mm by 0.3 mm
• Smaller than A. duodenale
• A pair of semilunar cutting plates on the ventral
  wall of the buccal capsule

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• Buccal capsule

Ancylostoma duodenale
Necator americanus
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Morphology Egg

• oval or can-shaped with a thin, hyaline shell,
  measured 60-75 by 36-40 µm.

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Life cycle
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Life cycle

• No intermediate host is necessary
• Larva takes a free living mode
• The filariform larva is the infective stage
• Infection routes skin penetration(mainly)
  orally swallow maternal-child
• Residing in human upper small intestine
  duodenum, jejunum
• Blood-Lung migration skin --- lymphatic system
  --- right side of the heart --- lung ---
  respiratory tree --- coughed up and swallowed ---
  small intestine
• Persisting migrans(????) Ancylostoma duodenale

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Pathogenesis

• 1. Hookworm larvae dermatitis
• Penetration of the skin by the filariform
  larvae may be asymptomatic in previously
  uninfected individuals.
• However, those experiencing repeated
  infections develop itching, known as "ground
  itch" or "dew itch".

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Pathogenesis

• 2. Migration of pre-adult cause temporary
  pulmonary inflammation
• In heavily infected individuals
• (i.e., 500-1000 worms), there can be symptoms
  of pneumonia during the migratory phase in the
  developmental cycle of these worms

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Pathogenesis

• 3. Abdominal pains, diarrhea, loss of appetite
• 4. Anemia
• Especially in young children
• Hypoproteinemic because of some loss of serum
  proteins
• Iron-deficiency

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• Why the small worms can cause anemia?
• The pump-like action when worms suck blood
• The worms secrete an anticoagulant, which
  facilitates bleeding
• The worms usually change the sites when suck
  blood
• 5. Allotriophagy (Geophagy) due to the
  iron-deficiency
• 6. Ancylostomiasis in infant

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Allotriophagy
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Laboratory diagnosis

• Brine floatation is the method of first choice
• Hookworm larvae cultivation is used for species
  identification
• Hookworm larvae in sputum

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Epidemiology

• Most prevalent in the tropical and subtropical
  zones
• In China, mostly mixed infected, while
  A.duodenale is somewhat northward distributed and
  N. americanus in southward

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Epidemiology

• Moist, shady, sandy, or loamy soil favors
  persistence of these worms
• Larvae can survive for up to 6 weeks
• Do not live long in clay, dry, hard packed
  soils, or where temperatures are freezing, or are
  higher than 45?C

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Principles of Control

1. Chemotherapy Albendazole Mebendazole
2. Sanitary disposal of human feces is the most
   effective control measure in preventing the
   spread of infection with the hookworms
3. Protection of the susceptible population