Parasitism

Department of Parasitology

Guangxi Medical University

HUMAN PARASITOLOGY Huan huan Shi (石焕焕)

HUMAN (MEDICAL) PARASITOLOGY a branch of the medical sciences dealing with the members of the animal kingdom living in and on the body of humans and with aspects of this host-parasite relationship having medical significance.

A science to study the parasitism.

HARMFULNESS OF PARASITES TO HUMAN BEINGS Six important tropical diseases defined by WHO: 1 Malaria 2 Schistosomiasis 3 Filariasis 4 Leishmaniasis

5 Trypanosomiasis 6 Leprosy

parasitosis

INTRODUCTION TO HUMAN PARASITOLOGY

Hope you can answer following questions after my lecture today. 1.What is the parasitism ? 2.Definition of parasite, host, life cycle and infective stage. 3. How do the parasites injure human beings? 4. How do the parasites infect host?

5.How to prevent and control parasitosis?

1

PARASITISM, PARASITE AND HOST

PARASITISM The relationship between animals that live together (From viewpoints of benefit and harm) Commensalism: an association which is benificial to one partner and no harm to the other.

Mutualism: reciprocal benefit between the two organisims.

Parasitism: One partner derives benefit. Another is injured. Parasitism involves two factors: parasite and host

PARASITE and HOST Among the partners in the parasitism,the one which benefits from the other is a parasite,while the one which harmed by the parasite is a host. CLASSIFICATION OF PARASITES: 1 Basing on the biologic taxonomy (1) Medical protozoa

(2) Medical helminths (3) Medical arthropods

2 Basing on the relationship between parasite and host (1). Obligative parasites : Malaria parasite

(2). Facultative parasites: Strongyloides stercoralis (3). Endoparasite: Ascaris Lumbricoides (4). Ectoparasite: Mosquito ,Fly, Flea. (5). Opportunistic parasite : Toxoplasma gondii

Types of hosts Definitive host: those provide the living of adult helminth or sexual stage of a protozoan. Intermediate host: those provide living of larvae of helminth or asexual stages of a protozoan. First and second intermediate host Reservoir host : those animal hosts of human parasites in which parasites are kept alive for long period of time with frequent excretion of the eggs or pathogens(serve as a source of infection for humans ).

2

LIFE CYCLE AND INFECTIVE STAGE

Life cycle: The whole biological course of growth, development and reproduction of a parasite. Infective stage: The stage that is able to infect men in life cycle.

Sporocyst rediae

The life cycle of C.sinensis: (A) definitive host (B) Reservoir host (C) The first intermediate host (D) The second intermediate host (1) Adult (2) Egg (3) Cercaria which have become free (4) metacercaria

3

THE RELATIONSHIP BETWEEN PARASITE AND HOST

1. Effects of Parasites on Host A. Uptaking nutrition B. Physical trauma C. Chemical and allergic effects: a) Lytic necrosis : Enzymes b) Stimulation of host tissue reaction: c) causing hypersensitivity

2.Effects of Host on Parasite ---- immunity (refer to immunology)

Feature of parasitic immunity 1. Complication of antigens 2. Non-sterilizing immunity is commoner: premunition (malaria),concomitant immunity (schistosoma) 3. Re-infection occurs often

Results from reaction between parasite and host 1. Parasite will be eliminated

2. Keep balance ( suppressive infection ,carrier) 3. Parasitosis

4

EPIDEMIOLOGY OF PARASITOSIS

1. Factors of transmission Source of infection parasite Subjects of individuals

Pathways of transmission

(1) Source of infection A. patients B. carrier C. reservoir host (2) Pathways of Transmission A. Oral route: Contaminated soil, food and water etc. mediate it.

Soil polluted with human excreta is commonly responsible for exposure to infection with Ascaris lumbricoides, Trichuris trichiura Water may contain viable cysts of parasitic ameba, intestinal flagellates, Taenia solium eggs. Fresh-water fishes are sources for several types of intestinal and liver flukes;

Crabs and crayfishes are sources for the oriental lung fluke; Raw pork is the source for Trichinella spiralis and Taenia solium; beef is the source for Taenia saginata; buffalo nuts are the source for the giant intestinal fluke (Fasciola buski),

B. Skin and mucous membrane route (a) Penetration of the intact skin : filariformlarvae of hookworm,Strongyloides stercoralis on coming in contact with fecal polluted soil. (b) Piercing the skin: cercariae of Schitosoma japonicum,S.mansoni and S.haematobium on coming in contact with infected water.

C. Inoculation by an arthropode vector The parasite is introduced percutaneously when the arthropod punctures the skin to feed, i.e. malaria parasites , the leishmanias, trypanosomes and filariaes. D. Other route (a) Inhalation of air-borne eggs of Enterobius vermicularis into the posterior pharynx;

(b) Transplacental (congenital) infection : Toxoplasma gondi, and occasionally with malaria parasites, blood flukes and others; (c) Blood transfusion: malaria. (d) Transmammary (milk) infection : Strongyloides, Ancylostoma, and certain trematodes. (e) By sexual intercourse: Trichomonas vaginalis.

(3) Susceptible population or Subjects of individuals Humans or animals who are weakly or defectively resistant to certain parasites.

2. Prevention and control 

Prevention of parasitic disease refers to its interception  Control refers to check the possibilities of dissemination of infection and epidemics,reduce and maintain a low level of parasitic infections prevalent in human population

Three measures should be implemented: (1) Treatment of the source of infection; (2) Blockade of the pathways of transmission; (3) Protection of the susceptible population.

Summary Could you answer the 5 questions? 1.What is the parasitism ? 2.Definition of parasite, host, life cycle and infective stage. 3. How do the parasites injure human beings? 4. How do the parasites infect host? 5.How to prevent and control parasitosis?