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Introduction to Human Parasitology Yihui Luo yihuiluo@zju.edu.cn Department of Medical Microbiology and Parasitology, Medical College, Zhejiang University. Why do you need to learn Medical Parasitology ?. Examples of Medical Importance in the World.
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Introduction to Human Parasitology Yihui Luo yihuiluo@zju.edu.cn Department of Medical Microbiology and Parasitology, Medical College, Zhejiang University
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)
Prevalence of parasitic infections 6 Major Tropical Diseases (WHO and TDR) • Malaria • Schistosomiasis • Filariasis • Leishmaniasis • Trypanosomiasis • Leprosy
Malaria • Infected, 300 to 500 million • Annual deaths 2.2 to 2.5 million
Schistosomiasis • Infected, 150 million • Annual deaths, 500,000 to 1 million patient with ascites
Lymphatic filariasis • 128 million infected patients with elephantiasis and hydrocele testis
Leishmaniasis • Infected, 1.2 million Amastigote in the phagecyte skin lesion
Trypanosomiasis • Infected, 13 to 50 thousands • sleeping-sickness
Parasitic Diseases in China • Infective rate: 19.56% • Infective number: 1.29 million (According to a parasitic survey from 2001.4 to 2006.12)
Examples of Medical Importance in China China’s parasite infection based on the nationwide parasite survey
Why do we study parasites? • Inability to raise livestock in Africa has led to poverty • Debilitating effects of parasitic diseases on humans results in a loss of labour • Bringing huge economic losses Thus, an understanding of parasites is important to students in biology, the medical sciences, the veterinary sciences, and public health.
You need to know 7 questions as follows in the course of human parasitology • What isparasitology? • 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 and diseases. • What are principles of control of parasitic diseases?
Definition of Parasitology • It studies the pathogenic parasites and their relationships to the hosts and environment. • Parasites traditionally have included the study of three major groups of animals: parasitic protozoa , parasitic helminthes(worms) , and those arthropods that directly cause disease or act as vectors of various pathogens. • It encompasses aspects of biology, pathogenesis, diagnosis, epidemiology, treatment, prevention and control. Parasitology is usually in the scope of preventive medicine and the foundation of clinical parasitic diseases .
Helminthes(multicellular) Nematode Trematode Cestode Acanthocephala Important Groups of Human Parasites Protozoa(unicellular) • Amoeba • Flagellate • Sporidium • Ciliate Arthropoda • Mosquito • Fly • Tick • Mite • Bug • Flea • Lice
Contents of learning parasitology Biology of parasites Ecology of parasites (parasite –host and –environment interaction) Pathogenesis Laboratory diagnosis (etiological, immuno- and molecular diagnosis) Epidemiology and disease control
Denomination of parasite Linnaeus binomial nomenclature, in Latin, with the genus name (nominative form) given first, followed by the species name (possessive form). Entamoeba + histolytica Writing in italic type
Evolution of parasitism Understanding start withbasic 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 live together in an intimate association
Three major categories of symbiosis Symbiosis living together 1. Mutualism-- both partners benefit from the association （互利共生） Example:the flagellate live in the intestine of the termite 2. Commensalism-- one partner benefits from its (偏利共生) relationship with the other(host), but the host neither benefits nor is harmed. Example: remora fish associated with sharks feeds on leftover food
3. Parasitism-- one partner (parasite) actually does benefit from the association and harm the other ( host) Example: Ascarias lumbricoides lived in the intestine of human.
Symbiosis (sum.) • + and + = Mutualism. Both species benefit from the interaction between the two species. • + and 0 = Commensalism. One species benefits from the interaction and the other is unaffected. • + and - = Parasitism. One species benefits from the interaction and the other is adversely affected(harmed). The categories of symbiosis are man-made constructed to introduce primarily for convenience. In fact, they can be overlap between various categories.
Parasite — In the relationship known as parasitism, the partner gains benefit, always smaller, is the parasite which to some degree injures its partner and the other to be injured at the same time is known as the host. — 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).
—Parasites may be classified according to different ways: • ecology--- Obligate /facultative • resiting site---endoparasite / ectoparasite • durationof parasitism---permanent/ temporary
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
—types of the host • Definitive/final host is the host in which the parasite become sexually mature (where the adult worm harbor or undergoing sexual reproduction) • Intermediate host is the 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. Typically, the intermediate host must be eaten to transmit the parasite to the next host.
some protozoa and many helminthes have complex life cycles, with not one but two and sometimes more hosts, when more than one host species is necessary to the development of the parasite, that host in which sexual stages of protozoa or adult helminth occurs is called the definitive host; and that host in which larvae stages of helminth or asexual stages of protozoa occurs is called the intermediate host (they are usually designated first and second intermediate hosts if there is more than one).
Reservoir host is referred to those animal hosts of human parasites, in which parasite are kept alive for long period of time with frequent excretion of the eggs or pathogens. Therefore reservoir hosts are potential source of infections in human being. Example: a buffalo, the definitive host of Schistosoma japonicum, harbor the parasite that can be transmitted to humans
Host and 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)
Generalized stages of a parasite’s life cycle Stage in human host (linking to pathogenesis) Stage to discharge (linking to etiological diagnosis) Stage developing outside human host ( in external environment, intermediate host or insect host)--- (linking to transmission) Stage infecting men (infective stage) Infective stage: A stage of parasite which can enter the human body and develop continuously there. (infective eggs containing larval stage)
—The types of life cycle of parasites Direct type: one host (definitive host) Indirect type: more one hosts(intermediate host(s) and definitive host) ---geo-helminth ---bio-helminth
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.
Indirect type:Many parasites have more complex cycles which include 2 or more hosts and are classified as having indirect life cycles.
—Host-specificity of the parasite and susceptibility of the host, parasite may have highly specific requirement for the host species and residing site(a given parasite can only survive in the definite site of definite host species . It is known as the host-specificity to the parasite or the susceptibility to the host) —Zoonotic parasites some parasites can take human being as well as certain kind of animals as susceptible hosts, then it is known as zoonotic parasites and the diseases called as Zoonosis ( a group of diseases naturally transmitted between human and vertebrates)
An example of zoonosis Cysticercosis
Effects of the Parasite on the Host • Parasite infection and parasitic disease. • Overt symptoms of infection may depend on the number of worms present, the nutritional status of the host, or both. • Injury to the host may be brought about in many ways.
