Human Parasitology ( 人体寄生虫学 )

1. Human Parasitology(人体寄生虫学) Liwei Li Department of Medical Microbiology and Parasitology College of Medicine, Zhejiang University lilw2@zju.edu.cn

2. Introduction to Parasitology • F. E. G. Cox. History of Human Parasitology. Clin Microbiol Rev. 2002 October; 15 (4): 595–612 http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=126866 • Olson & Guselle. Are pig parasite a human health risk?http://www.banffpork.ca/proc/2000pdf/Chap13-Olson.pdf

3. 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?

4. Pathogens microbes parasites protozoa helminthes arthropods bacteria viruses fungi

5. Mosquito Pathogens Infectious or communicable diseases!

6. Definition of Parasitology Parasitologyis 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 parasitologyis 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

7. 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

8. Why do we study parasitology? • Parasites provide unique examples of biological phenomena not found in free-living organisms • _ • Medical importance • Veterinary importance • Economic importance

9. 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.

10. Medical Importance of Parasites • Ten major tropical diseases (UNDP/World bank/TDR, 2000) • Malaria(疟疾) • Shistosomaiasis（血吸虫病） • Filariasis(丝虫病，Lymphatic filariasis and Onchocerciasis) • Leishmaniasis（利什曼病） • Trypanosomiasis (锥虫病，African trypanosomiasis and chagas disease ) • Leprosy（麻风病） • Tuberculosis （结核病） • Dengue fever （登革热）

11. 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)

12. Examples of Medical Importance in the World

13. Medical Importance in China • Five major parasitic diseases • Malaria • Schistosomiasis • Kala-azar (黑热病) • Filariasis • Hookworm disease

14. Medical Importance in China

15. Medical Importance in China China’s parasite infection based on the nationwide parasite survey

16. 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.

17. WHAT TYPES OF LIVING ORGANISMS ARE PARASITIC? Parasites occur in two of the five kingdoms of living organisms. What are the 5 kingdoms?

18. 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……

19. 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

20. 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

21. Symbiosis (cont.) • 1. Mutualism(互利共生) • 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

22. Symbiosis (cont.) • 2. Commensalism(偏利共生,共栖) • 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

23. Symbiosis(cont.) • 3. Parasitism(寄生) • 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 it’s in turtles) or is it a parasite (when it’s 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.

24. Commensalism and Phoresis Mutualism Parasitism 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

25. 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).

26. —Parasites may be classified according to different ways: • residing site---endoparasite / ectoparasite • ecology---obligatory/facultative; accidental or • opportunistic • durationof parasitism---permanent/intermittent

27. 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

28. 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

29. Types of the host • A definitive host(终宿主) is the host in which the parasite become sexually mature (where the adult wormharbor or undergoing sexual reproduction). • An intermediate host(中间宿主) 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.

30. Definitions of Hosts (cont.) Reservoir host(保虫宿主) 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(人兽共患病): a disease of animals that may be transmitted to humans under natural conditions.

31. Definitions of Hosts (cont.) A transport/paratenic/transfer host (转续宿主) : 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 parasite’s life cycle

32. Definitions of Hosts (cont.) • Immune compromised hostsare 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.

33. 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)

34. Definitions of Hosts (cont.) Vectorparasite 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)

35. What is the Life Cycle Life cycledescribed 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

36. Generalized stages of a parasite’s 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)

37. Invading Pathogenesis Human residing stage Oral Skin Vector contact Site No. Infective stage Stage to discharge Via: feces Urine Sputum Vector blood (soil, water, animal host, insect) Extra-Human development Epidemiology Diagnosis Parasite Life Cycle—A generalized mode

38. 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

39. 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.

40. Life cycle (cont.) • Many parasites have more complex cycles which include 2 or more hosts and are classified as having indirect life cycles.

41. 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

42. The harmful effects on the host host-parasite interactions • Depriving for nutrition • Mechanical damage • Toxic effects • Immune-pathological consequences

43. Ascaris in small intestine

44. Hookworm and anemia

45. Complete blockage of intestine caused by Ascaris

46. Allergy caused by mosquito bites

47. schistosomiasis

48. host-parasite interactions • Effects of the host to the parasite • Genetic constitutionof 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 )

49. 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 (带虫免疫), concomitant immunity (伴随免疫)

50. 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