medical parasitology --introduction department of medical parasitology

Medical Parasitology--Introduction

Department of Medical Parasitology

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 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


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

http://images.google.cn/imgres?imgurl=http://www.alertbay.com/library/images/hospital.jpg&imgrefurl=http://www.alertbay.com/library/archives.htm&h=321&w=550&sz=59&hl=zh-CN&start=11&tbnid=JzNMWthU7WRdWM:&tbnh=78&tbnw=133&prev=/images%3Fq%3D%2BSt%2BGeorge%2527s%2Bhospital%2B%2B%26gbv%3D2%26svnum%3D10%26complete%3D1%26hl%3Dzh-CN%26newwindow%3D1%26sa%3DG

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 )

RBC

Protozoa

Plasmodium

Trematodes

cercariae

Schistosome

Paragonimus westermani

(Lung fluke)

TapewormTapeworm

Cestodes

Nematode

Ascaris lumbricoides

Hookworm

Medical Medical arthropods

Fly

MosquitoSandfly

FleaLouseHard tickSoft tick

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



*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.



*Tissue parasites ： 20+ species

brain : Angiostrongylus cantonensis

eye : Thelazia callipaeda

lung : Lung fluke

kidney : Dioctophyma renale

skin: Sarcoptes scabiei , etc.

……



* 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







eases


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


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.


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


Schistosomiasis

mesenteric veins via hepatic portal systemascites

Damage to the skin or muscle

Affect the growth , development/teratogenesis


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







eases


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







eases


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







eases


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.

medical parasitology --introduction department of medical parasitology

Documents

human parasitology

fish parasitology

veterinary parasitology

medical microbiology

medical entomolog

medical significance

pathogenic parasites

biology of parasites