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Introduction to Medical Parasitology
• Definition of medical parasitology
• Significances of medical parasitology
• Conceptions related to medical parasitology
• Relationships between parasites and hosts
• Basic factors of transmission of parasitic dis
eases
• Preventive measures of parasitic diseases
Introduction to Medical Parasitology
• Definition of medical parasitology
• Significances of medical parasitology
• Conceptions related to medical parasitology
• Relationships between parasites and hosts
• Basic factors of transmission of parasitic dis
eases
• Preventive measures of parasitic diseases
What is Parasitology? A parasite is an organism that live on or within a
nother organism called the host .
Parasitology is a science of studying parasitism a
nd a discipline dealing with the biology of parasites
(including its morphology, embryology, physiology,
biochemistry and nutrition, etc.), ecology of parasit
ism with emphasis on parasite-host and parasite-en
vironment interactions.
Since the parasites studied in this discipline involve
parasitic protozoa, parasitic helminthes, certain lesser
groups of worms, parasitic arthropods, and the vector
s of parasites, that is, parasitology is largely an amalg
amation of protozoology, helminthology, entomology a
nd acarology.
Parasitology has also been subdivided into medical
or human parasitology, veterinary parasitology, fish p
arasitology and plant nematology.
What is Parasitology?
What is Medical Parasitology?
Medical parasitology or human parasitology is re
stricted to studying those parasites that are living in
or on the body of humans and with aspects of the ho
st-parasite relationship having medical significance.
In other words, medical parasitology is the subject w
hich deals with the parasites that infect man, the dis
eases caused by them, clinical picture and the respon
se generated by man against them.
Pathogenic Biology In modern biomedicine, medical parasitology a
nd medical microbiology , which are integrated in
to pathogenic biology, are in the same scope of pat
hogenic organisms.
Pathogenic biology which focuses on the biologi
cal causes to human infectious diseases (biological
etiology), is usually comprised in preventive medi
cine and is also considered as the foundation of cli
nical infectious or communicable diseases and pu
blic health.
Pathogenic Biology Pathogenic biology involves the biological features o
f pathogenic organisms, the relationships between path
ogenic parasites and hosts and their environment, the p
athogenic factors and the related pathogenesis, the labo
ratory diagnosis, the transmission and prevalence, and
the prevention and control of these diseases infected wit
h pathogenic organisms.
• Microbiology--- Pathogen (Microbe) : viruses, bacteria,
and fungi.
• Parasitology--- Pathogen (Parasites) : protozoa, helmin
thes, and arthropods.
Medical Parasitology
Parasites Parasitic diseases
Morp
holog
y Life C
ycle
Path
ogenesi
s Diagn
osis
Treatm
ent
Tran
smissio
n Preven
tion
Medical protozoology
Medical helminthology
Medical arthropodology
Med
ical
para
sito
log
y
i.e. Medical entomology
Preclinical Public Health & ClinicalBiology Medicine Preventive Medicine Medicine
Pathogenic Biology
Medical Parasitology
& Medical Microbiology
Medical Parasitology in Medicine
Microbiology
Overseas Medical Education
• In USA, UK, and other countries, medical microbiology
includes medical microbiology and parasitology. Medic
al parasitology is not a independent curriculum.
Curriculum Reform in China• Before 1997, two independent curricula
• Since 1997, a compulsive curriculum---- Pathogenic biol
ogy.
• However, in our school, microbiology and parasitology
are two independent curricula in medical education.
Biology,Biochemistry,Anatomy,Histology,Physiology,Immunology
Medical Parasitology
Public Health & ClinicalPreventive Medicine Medicine
Medical Parasitology in Medical Education
Curriculum Plan
• Lectures ---- introduce main parasites
and related parasitic diseases
• Experimental observations ---- observe
the morphologic characteristics of
parasites by microscopy or naked eye
• Final examination
1. Wang Shiping & Ye Shiying. Textbook of Medical Microbio
logy and Parasitology (1st Edition) , 2006
2. Gerald D Schmidt & Larry S Roberts. Foundation of Parasi
tology (3rd Edition) , 8th ed, 2009
3. David T John, et al. Medical Parasitology (9th Edition) , 2
007
4. CDC Division of Parasitic diseases:
http://www.cdc.gov/ncidod/dpd/search/default.htm
5. DPDx: http://www.dpd.cdc.gov/dpdx/Default.htm
Recommended References
Early written records• 3000 to 400 BC, the first written records of parasitic infections come f
rom Egyptian medicine, particularly the Ebers papyrus of 1500 BC discovered at Thebes. Intestinal roundworms and tapeworms.
• 800 to 300 BC, writings of Greek physicians such as Hippocrates. Worms from fishes, domesticated animals, and humans.
• 3000 to 300 BC, writings of physicians from China.
• 2500 to 200 BC, from India.
• 700 BC to 400 AD, from Rome.
• Latter part of the first millennium, from the Arab Empire.
• Arabic physician Avicenna (AD 980 to 1037) , wrote important medical works that contain a great deal of information about diseases clearly caused by parasites. He recognized not only Ascaris, Enterobius, and tapeworms but also the guinea worm, Dracunculus medinensis.
History of Human Parasitology
Modern times
• Manson in 1879 filariasis
• Laveran in 1880 malaria parasite
• Ross in 1897 malaria life cycle
• Bruce in 1896-1902 and Chagas in 1908 trypanosomiasis
• Leishman and Donovan in 1900-1911 leishmaniasis ……
• 1879 (Ringer) , 1880 (Manson) : Paragonimus westermani
• 1875 (McConnell) : Clonorchis sinensis
• 1905 (Logan) : Schistosoma japonicum in China
……
History of Human Parasitology
In England Manson became Medical Advisor to the Colonial Office and in this capacity persuaded the then Secretary of State for the Colonies, Joseph Chamberlain, of the need for providing facilities in Britain for educating doctors in tropical diseases. One consequence of his influence was the creation of School of Tropical Medicine in both Liverpool and London in 1898Patrick Manson(1844-1922)
“Father of modern tropical medicine” The first President (and
Ronald Ross Vice-President) of the Society of Tropical Medicine and
Hygiene (1907)
The first to discover (1877–79) that an insect (mosquito) can be host to a developing parasite (the worm Filaria bancrofti) that is the cause of filariasis
Alphonse Laveran
1907 Nobel Laureate in Medicine
in recognition of his work on the role played by protozoa in causing diseases
Ronald Ross
1902 Nobel Laureate in Medicine
for his work on malaria, by which he has shown how it enters the organism and thereby has laid the foundation for successful research on this disease and methods of combating it
• 1911-12 (Dr. Fuqing Yan ): Local epidemic investigations on schistosomiasis and malaria around Changsha
• 1919-20 ( Dr. Fuqing Yan ) : Investigation and control researches on hookworm infection at Pingxiang county
• 1920-28 ( Beijing Xie-He medical college ): Department of Parasitic biology
• 1928 ( Dr. Shilv Hong ): Hangzhou institute of tropical disease, the first academic organization in China on parasitology
• 1932: Department of parasitology, Central experimental academy on hygiene
• Thereafter: Shanghai medical college, Lingnan university, Xiangya school of medicine, Western China medical school, Qilu university……
Human Parasitology in China
Classification of parasites
Protozoa
Parasites Helminthes
Arthropods
Nematodes
Trematodes
Cestodes
(Endoparasite)
(Ectoparasite)
(Unicellular)
(Multicellular )
229 species in total
Nematodes -- 35 species
Trematodes -- 47 species
Cestodes -- 16 species
Protozoa -- 41 species
Others -- 90 species Common human parasites -- around 80 species
Human parasites in China
----According to parasitic sites
*Intestinal tract parasites : 30+ species
Ascaris lumbricoides ( round worm ) Trichuris trichiura ( whip worm ) Enterobius vermicularis ( pinworm ) Hookworm
Fasciolopsis buski ( intestine fluke ) Taenia solium
Entamoeba histolytica, etc.
Classification in clinic
----According to parasitic sites
Classification in clinic
*Other tract parasites : 10+ species
esophagus : Uongylonema pulchrum
trachea : Mammomonogamus
biliary tract : Liver fluke
urogenital tract : Trichomonas vaginalis, etc.
* Blood vessel parasites : 5+ species
Schistosome, Filarial worms,
Angiostrongylus cantonensis, etc.
----According to parasitic sites
Classification in clinic
*Tissue parasites : 20+ species
brain : Angiostrongylus cantonensis
eye : Thelazia callipaeda
lung : Lung fluke
kidney : Dioctophyma renale
skin: Sarcoptes scabiei , etc.
……
----According to parasitic sites
Classification in clinic
* Intracellular parasites : 7+ species
Plasmodium
Leishmania
Toxoplasma gondii
Trichina spiralis, etc.
* Ectoparasite / Vectors : 60+ species
Louce, Flea, Mosquito, Fly, Sand fly, Tabanid fly, Tick, gamasid mite , etc.
• International travel
• Contamination of water supply
• Immigrants from endemic areas
• Popularity of household pets
• Increasing popularity of exotic regional foods
• Use of antibiotics and immuno-suppressive drugs
• Spread of AIDS
• Undercooked meats and raw fish
• Ingestion of improperly washed fruits, vegetables
Where and how we can get parasites
Introduction to Medical Parasitology
• Definition of medical parasitology
• Significances of medical parasitology
• Conceptions related to medical parasitology
• Relationships between parasites and hosts
• Basic factors of transmission of parasitic dis
eases
• Preventive measures of parasitic diseases
1. Common ailment and frequently encountered disease
Why should we study Parasitology?
Hainan Guangxi Fujian Sichuan 94.7 86.2 85.3 82.0Guizhou Zhejiang Jiangxi 81.0 81.1 79.5 Hunan Guangdong Heilongjiang
76.7 72.1 17.5%
The first survey on parasitic infection completed in 1992 indicated the total infection rate of human parasites in China was 62.63%, number of infections was about more than 700 million, geohelminthes infection for the most
Why should we study Parasitology?
Through comprehensive prevention and control
in China, total worms infection rate in 2004 dropped
from 55.27% to 21.4% . Estimated total number of
infections of roundworm, hookworm , whipworm
dropped from 536 million in 1990 , to about 129
million people (76% reduction ). But in central and
southern China, soil -borne nematode infection rate
was still as high as 20.1 % to 56.2%
1. Common ailment and frequently encountered disease
In 1947, N. Stoll estimated the total number of infections of roundworm, whipworm and hookworm were 644 million (30%) , 355 million (16%) , 457 million(21%), respectively. Fifty years later, in 1997, the numbers were 1273million (24%) , 902million (17%) and 1277million (24%) , respectively. The prevalence of intestinal nematodes did not change, and there was a significant increase in the actual number of infections, almost in developing countries.
Why should we study Parasitology?
2. Severe consequence of parasitic infection
Parasitic infection result in the decline of wor
k ability and quality of life, teratogenesis , disa
bility, death , and carcinogenesis induction
Damage to vital organs
BrainBrain
EyeEye
LungLung
LiverLiverHeartHeart
EyeEye
Why should we study Parasitology?
Why should we study Parasitology?
3. WHO/TDR focuses on infectious diseases
Accoding to WHO statistics , parasites are the cause of more
human deaths than anything else apart from HIV/AIDS and tu
berculosis(TB), one living person in ten suffers from one or mor
e of eight major tropical diseases:
malaria, schistosomiasis, lymphatic filariasis, onchocerciasis,
leprosy, sleeping sickness,Chagas disease,and leishmaniasis
<<Parasitology Today>> , http://www.who.int
The main target diseases of WHO communicable disease programs
• Malaria
• Schistosomiasis and intestinal parasitic infections
• Filariasis (lymphatic filariasis, onchocerciasis)
• Leishmaniasis
• Trypanosomiasis (sleeping sickness, Chagas disease)
• Dracunculiasis
• Leprosy
• Tuberculosis
• Poliomyelitis, AIDS,Dengue fever, etc.
Threatened Endemic countries Deaths dalys(Burden of disease)
population (million) (thousand) (million)
Malaria 2400 100 1156.8 42.80
Schistosomiasis 650 74 14.0 1.77
Trypanosomes 600 36 52.4 1.67
Filaria 1000 80 1.35
Ascaris 3.8 1.31
Trichuris 2.4 1.16
Hookworm 4.6 1.05
Dalys: Disability adjuststed life years
--Reflect the extent of parasitic diseases on the health damage
“Top ten” of human parasites, based on WHO estimated
Tropical diseases are still neglected by scientific
community and medical education, and are still
relatively isolated from the mainstream of modern
biomedicine in the western world, as well as in the
developing world, including China, but they remain
one of major health problems in the world and
particularly, still rank exceedingly high in most of
developing countries
Still neglected !
Neglected Tropical Diseases (NTD)
Burden of disease due to NTDs
World Health Report
• Lymphatic Filariasis 5,654,000• Soil-transmitted helminthiasis 4,706,000• Kala-azar 2,357,000• Trachoma 2,329,000• Schistosomiasis 1,760,000• African Sleeping Sickness 1,598,000• Onchocerciasis 987,000• Chagas Disease 649,000• Leprosy 177,000• Buruli Ulcer <100,000• Guinea-worm <100,000 Total Neglected Disease 20,217,000• HIV-AIDS 84,429,000• Malaria 42,280,000
Revised estimates (The Lancet)
• Hookworm disease 22.1 million• Ascariasis 10.5 million• Trichuriasis 6.4 million• Lymphatic Filariasis 5.8 million• Schistosomiasis 4.5 million• Trachoma 2.3 million• Leishmaniasis 2.1 million• Trypanosomiasis 1.5 million• Chagas Disease 0.7 million• Onchocerciasis 0.5 million• Leprosy 0.2 million
• Dracunculiasis <0.1 million• Total 56.6 million
Diseases ( patients ) 1950 2008
Malaria 30 million 26478
Schistosomiasis 11.60 million 0.39 million
Filariasis 30.99 million basically eradicated in 1994
(0.1 million , 1999 )
Leishmaniasis 0.53 million basically eradicated in 1958
524
Hookworm disease 190 million (infection rate 70%) 39.3 million ( 2004 )
Hydatid disease: 0.6 million, Ascariasis: 86 million , Hookworm disease: 39.30 million, Trichuriasis: 29million (2004)Clonorchiasis:12.5 million (2005)
Why should we study Parasitology?4. “Top five” parasitic diseases in China
Introduction to Medical Parasitology
• Definition of medical parasitology
• Significances of medical parasitology
• Conceptions related to medical parasitology
• Relationships between parasites and hosts
• Basic factors of transmission of parasitic dis
eases
• Preventive measures of parasitic diseases
Conceptions related to medical parasitology
• Symbiosis
• Parasite and type of parasites
• Host and common type of host
• Life cycle and type of life cycle
Symbiosis
The relationship between two living things (animals). Two living things live together and involve protection or other advantages to one or both partner.
• Commensalism
• Mutualism
• Parasitism*
Commensalism Both partners are able to lead independent lives,
but one may gain advantage from the association when they are together and least not damage to the other
A female pea crab in the mantle cavity of its mussel host. The crab does not damage the mussel and uses its shell purely for protection
Mussel
Mutualism
An association which is beneficial to both living things
A selection of ciliates from the rumen of cattle or sheep. The rumen contains enormous numbers of ciliates that break down cellulose in the feed
Parasitism
An association which is beneficial to one
partner and harmful to the other partner.
The former that is beneficial to is called
parasite, the latter that is harmful to is
called host.
e.g., Human / Hookworm
Protozoa
Parasites Helminthes
Arthropods
Nematodes
Trematodes
Cestodes
(Endoparasite)
(Ectoparasite)
(Unicellular)
(Multicellular )
Parasite and the type of parasites
Parasite: an animal that is dependent on
another animal (host) for its survival
Other classification
Parasites may be classified according to different ways:
• Obligate parasite: a parasite which cannot survive in any other manner, e.g., filaria
• Facultative parasite: an organism which may exist in a free-living state and which if opportunity presents itself may become parasitic, e.g., Strongyloides stercoralis
Endoparasite and ectoparasite
A parasite which lives in or on the bod
y of the host is called endoparasite (proto
zoa and helminthes) or ectoparasite (arth
ropods)
Host and type of host
• Intermediate host : the host harboring the
larvae or asexual stage of parasite
• Final host (definitive host) : the host harbo
ring adult or sexual stage of parasite
Host : an organism that harbors the parasite usually larger than the parasite
Host and type of host
• Reservoir host : animals harboring the same species of parasites as man, e.g., schistosome/human, buffalo
Potential sources of human infection• Paratenic host (transport host) : a host which act
s as a transporting agent for the parasite and in which, the parasite, usually a larval stage, dose not undergo any further development but if they could go into a final host by accident it would continue to develop till sexual maturity, e.g., Paragonimus Westermani /human, wild boar
Life cycle and type of life cycle
• The direct type : only one host (final host, no i
ntermediate host). e.g., Ascaris lumbricoides, H
ookworm, and Enterobius vermicularis
• The indirect type : life cycle with more than on
e host (intermediate host and final host) . e.g.,
plasmodium, lymphatic filaria
Life cycle : the whole biological course of growth, development and reproduction of a parasite
Introduction to Medical Parasitology
• Definition of medical parasitology
• Significances of medical parasitology
• Conceptions related to medical parasitology
• Relationships between parasites and hosts
• Basic factors of transmission of parasitic dis
eases
• Preventive measures of parasitic diseases
Relationship between parasite and host
injure to
Parasites harbour in Host (animal or human)
immune responses
• Effects of the parasites on the host
• Effects of the host on the parasites
Effects of parasites on the host
• Depriving the host of essential substance
Hookworm Suck blood Anemia
• Mechanical damage of parasites on the host
Ascaris Perforate/Obstruction
• Toxic
Entamoeba histolytica Proteolytic enzyme Necrosis
• Inflammation and hypersensitivity
Parasite antigen Immune system
e.g., Anaphylaxis
Immune response
Allergy/ Hypersensitivity
Uptake of nutrition
• Pathogens utilize nutrition from host
environment for their development and
reproduction.
• Helminthes (nematodes or flukes --- have a gut
and mouth) feed upon the surrounding tissues,
body fluids or even host cell debris.
• Tapeworms (no gut or mouth) reply on the
host’s daily intake by their body wall absorbing
for their own food.
Mechanical damage of parasites
• Entering the cells: some protozoa must live in certa
in cells and reproduce. Finally result in the rupture
of the host cells.
• Migration or penetration through tissue or organ
• Blockage and pressure: the intestinal lumen can be
blocked by worms. Hydatid cyst in liver may reach
volumes of 1-2 litres, it can cause severe damage to
organ.
Toxic and hypersensitivity
• Toxin: many parasites can introduce or secret
toxin and cause damage to host.
• Hypersensitivity: the metabolites, secretion,
excretion or other products of parasites or dead
worms may act as foreign antigen, to stimulate the
immune system of host to produce immune
response or hypersensitivity. Hypersensitivity is
harmful to host, which may lead to severe or even
fatal reaction.
Sudden rupture of hydatid cysts with release
of large amounts of fluid could result in severe
allergic reaction, sometimes lead to shock or dea
th of patients
Effects of the host on the parasites
• Innate immunity
• Acquired immunity
The host can produce certain degree resistance to parasites in human body or re-infection. The resistance (Immunity) is not very strong. In general, It does not wipe out parasites completely, but may limit the number of parasites and establishes balance with parasites
Innate immunity
• Barrier : prevent parasites to invade in certain
degree. skin/mucous, membrance/placenta
• Acid in skin or stomach can cause damage of th
e parasites
• Phagocytosis of phagocyte
Non-specific/effective against a wide range
of parasitic infection/controlled by genetical fa
ctors. But not very strong
Acquired immunity
Mechanism : cellular and humoral immunity
• Sterilizing immunity : wipe out the parasites co
mpletely, meanwhile get a long-term specific res
istance to re-infection. Rare!
• Non-sterilizing immunity : wipe out most of the
parasites, but not completely. Common! No par
asite, no immunity
Introduction to Medical Parasitology
• Definition of medical parasitology
• Significances of medical parasitology
• Conceptions related to medical parasitology
• Relationships between parasites and hosts
• Basic factors of transmission of parasitic dis
eases
• Preventive measures of parasitic diseases
Basic factors of transmission of parasitic
diseasesParasitic diseases Infectious diseases Transmission
• The source of the infection
• The routes of transmission
• The susceptible host
The combined effect of those factors determine the disp
ersal and the prevalence of the parasites at a given time an
d place and regulate the incidence of the parasitic diseases
in certain local population.
Source of the infection
• Patient : persons who have parasites in their bo
dy and show clinical symptoms
• Carrier : persons who have parasites in their b
ody, not show symptoms
• Reservoir host : animals that harbor the same s
pecies of parasites as man, the parasites in ani
mals sometimes can be transmitted into human
Routes of transmission • Congenital transmission : from mother to infan
t , e.g., toxoplasmosis
• Contact transmission : direct contact or indirec
t contact with patients or infected animals, e.g.,
Trichomonas vaginalis
• Food transmission : the infectious stage of para
sites contaminated food / the meat of the interm
ediate hosts containing infectious stage of paras
ites , e.g., Clonorchiasis
• Water transmission : drink or contact the water
contaminated the infectious stage of parasites, e.
g., schistosome, Entamoeba histolytica
• Soil transmission : soil contaminated by feces co
ntaining the certain stage of parasites which can
develop into infective stage, e.g., Ascaris lumbric
oides , hookworm
• Arthropod transmission : vectors of certain para
sitic diseases, e.g., plasmodium
Routes of transmission
Susceptible host
In general, people is the susceptible host (Why?).
The parasite reaching a susceptible host must gain e
ntrance and set up a favorable residence in order to
complete its life cycle and cause the transmission of
parasitic diseases.
Avenues of invasion
• Digestive tract : most common avenue of entran
ce. (food/ water transmission)
• Skin : infective larvae perforate skin and reach t
o body and establish infection. (soil/ water/ cont
act transmission)
• Blood : bloodsucking insects containing infective
parasites bite the skin and inject parasites into h
uman blood. (arthropod transmission)
Prevention measures of parasitic diseases
• Controlling the source of the infection: treatment o
f the patients, carriers and reservoir hosts
• Blocking the routes of transmission: managing fece
s and water resource, controlling or eliminating vec
tors and intermediate hosts
• Protecting the susceptible hosts: paying attention to
health education/ personal hygiene, changing bad
working/ eating habit, etc.