Introduction to infectious agents

1. Introduction to infectious agents Prof.J.Sarath Edirisinghe MBBS (Cey), MSc (Lond), PhD (Lond), MD (Col) Consultant Medical Parasitologist Para-clinical Coordinator Faculty of Medicine & Allied Sciences, Rajarata University of Sri Lanka Saliyapura, Anuradhapura

2. Infectious agents Prions Viruses Micro-organisms Bacteria Protozoa Macro-organisms Helminths Arthropod vectors

4. Macro-organisms Helminths

6. Parasitism Parasitism is an association between two organisms of different species which is beneficial to one organism and harmful to the other. .The organism that is benefited derives food (metabolically dependent) and shelter (physically dependent) from the other

7. Parasite A parasite is an organism that derives food and shelter through a parasitic relationship and usually is the smallest of the associating pair.

8. Ectoparasite Lives outside the body Endoparasite Lives inside the body

9. Facultative parasite A facultative parasite is one which is not totally dependent on the host and is able to adapt to a free-living existence (depending on the favorability of the environment) Obligatory parasites These parasites are totally dependent on the host and are unable to live without the host.

10. Host In a parasitic association the larger organism of the associating pair is called a host and is the one that provides food and shelter to the parasite

11. Definitive host A definitive host is the one in which sexual multiplication of the parasite takes place Intermediate host IH is the one in which the larval stages of the parasite are present or in which asexual multiplication of the parasite takes place

12. Vector When one host is involved in the transmission of a parasite from one host to another, it is called a vector

13. Biological vector Sometimes a parasite completes a part of its life cycle while being transported by a vector. Such a host is called a biological vector

14. Mechanical vector When a parasite is merely transported without any change in the stage of the parasite, the vector is called a mechanical vector

15. Infection Infection is defined as the presence of living parasites in the body of the host Disease The manifestations the host experiences as a result of infection collectively constitutes a disease

16. Clinical sign Clinical symptom

17. Parasite transmission 1. Active penetration 2. Ingestion of infective stages found in the environment via food or water 3. Transmission by blood sucking vectors 4. Transmission by mechanical vectors 5. By close contact with infected persons and via clothing and bedding

18. 6. By inhalation of the infective stage into posterior pharynx followed by swallowing 7. Via sexual intercourse 8. Transplacental or congenital transmission 9. By way of blood transfusion

19. Malaria Lymphatic filariasis Roundworm infection - Ascariasis Hookworm disease Pinworm infection - Enterobiasis Giardiasis Cutaneous leishmaniasis Trichomonas vaginalis infection -trichomoniasis

20. Whipworm infection - trichuriasis Scabies Amoebiasis Dirofilariasis

21. Geographical distribution of parasitic infections - Sri Lanka Malaria- traditionally dry zone <1750mm annual rainfall Filariasis -South western coastal belt - ‘filarial belt’

22. Books recommended - • Manson’s Tropical Diseases • Worms and Disease by Ralph Muller • Parasites of Man by Sarath Edirisinghe • These books are available in the Saliyapura library. Therefore do notbuy!!