Parasite Pathogenicity PDF

Parasite Pathogenicity DR. LORINA BADGER-EMEKA. COM/KFU  Learning Objectives ▪ Students should be able to: ▪ know factors that are important for parasite pathogenicity ▪ differentiate between the common modes of parasite entry into the human host ▪ Describe three p...

Parasite Pathogenicity DR. LORINA BADGER-EMEKA. COM/KFU  Learning Objectives ▪ Students should be able to: ▪ know factors that are important for parasite pathogenicity ▪ differentiate between the common modes of parasite entry into the human host ▪ Describe three pathologic mechanisms important in parasitic diseases  Introduction 1 ▪ Unlike bacterial and viral infections, ▪ parasitic infections are often chronic ▪ and could last from months to years. ▪ Repeated exposure results ▪ in an ever-increasing parasite load. Introduction 2 Pathogenesis of protozoan and helminthic disease is highly variable. Although the various human parasites exhibit a wide range of direct pathogenic mechanisms, in most instances, the organisms themselves are: Not highly virulent, are unable to replicate within the host, or have both characteristics.  Parasite pathogenicity 1 The severity of illness caused by many parasites is related to a number of contributing factors: ▪ Infecting dose and ▪ the number of organisms acquired over time. ▪ parasitic infections are often chronic, ▪ lasting months to years. Parasite Pathogenicity 2 Murray 8th Ed. Parasite Pathogenicity 3 ▪ Parasites are almost always exogenous to the human host ▪ Thus, must enter the body through ingestion ▪ Or ▪ direct penetration of anatomic barriers. ▪ Many parasites have active, ▪ self-directed means of invading the human host. Murray 8th Ed. Factors Important For Parasite Pathogenicity Penetration of anatomic barriers  Ingestion Direct penetration Giardia spp., Entamoeba Hookworm, Strongyloides spp., histolytica, Cryptosporidium spp., schistosomes cestodes, nematodes (Ascaris)  Arthropod bite: Malaria, Babesia spp., Transplacental penetration: filaria, Leishmania spp. Toxoplasma gondii Parasite penetration  Question 1 Which one of the following Protozoan is mainly transmitted by sexual contact? A. Dientamoeba histolytica B. Retortamonas hominis C. Trichomonas vaginalis Summary How parasites enter into the body  Parasite inoculum Mosquito [Malaria Parasite] Sand fly [Leishmaniasis]  Question 2 By which on of the following route will Schistosoma haematobium cercariae be transmitted? A. Air inhalation B. Food ingestion C. Skin penetration Factors Important For Parasite Pathogenicity 3-Attachment (Adherence) & Replication  Parasite attachment and invasion 1 ▪ Once they have invaded, ▪ parasites attach to specific host cells ▪ or organs. ▪ They avoid immune detection, ▪ replicate (most protozoa and some helminths), Courtesy: Murray 8th ed Ancylostoma duodenale Courtesy: Murray Parasite attachment and invasion 2 ▪ produce toxic substances that destroy tissue, ▪ and ▪ cause disease secondary to the host’s own immunologic response. In addition, some parasites physically obstruct , and damage organs and tissues because of their size alone ADHERENCE AND REPLICATION Parasitic infections are initiated by the attachment of the organism to host tissues, followed by replication to establish colonization. The life cycle of a parasite is based on species and tissue tropisms, which determine the organs or tissues of the host in which a parasite can survive.  Pathogenicity Adherence and Replication: parasitic infections are initiated by the attachment of the organism to host tissue. Following attachment, The parasite may undergo replication as the next step in establishing an infection. Most protozoan parasites will replicate either intra or extra cellularly in the human host Replication is generally not observed with the helminths Some Pathologic Mechanisms in Parasitic Disease Pathologic mechanism by Protozoa. For example, the intestinal parasite E. histolytica produces proteinases that can degrade epithelial basement membrane As well as cell-anchoring proteins which disrupt epithelial cell layers In contrast to the protozoan parasites, many of the pathogenic consequences of helminthic infections are related to the size, movement, and longevity of the parasites.  Damage by Helminths The most obvious forms of direct damage from helminthic parasites are: 1. Those resulting from mechanical blockage of internal organs 2. OR from the effects of pressure exerted by growing parasites. Likewise, blockage of lymph flow which leads to elephantiasis, is associated with the presence of adult Wuchereria organisms in the lymphatic system. Intact adult Diphyllobothrium latum. (courtesy Murray) Tissue Damage (elephantiasis of the leg)  Other Pathologic Mechanisms Migration of helminths (usually larval forms) through body tissues, such as the skin, lungs, liver, intestines, eyes, and CNS, can damage the tissues directly and initiate hypersensitivity reactions. Finally, chronic inflammatory changes around parasites such as Opisthorchis sinensis and Schistosoma haematobium have been linked to the induction of carcinomatous changes in the bile ducts and the bladder, respectively.  Schistosoma mansoni Lateral spined egg Adult male and female worms Cercariae  Establishing a parasitic disease Parasitic disease can be established by: Elaboration of toxic products Mechanical tissue damage And immunopathologic reactions Factors Important For Parasite Pathogenicity [Cell and Tissue damage]  Factors Important For Parasite Pathogenicity 5-Disrutpion, Evasion & Inactivation of host defenses Antigenic Variation Molecular mimicry Antigenic masking Acquisition of coating of host Variation of surface antigens within the (Parasite evasion) molecules host e.g: malaria, Giardia Eg. Schisotosomes & Hydatid Cyst Microbial antigens mimicking host antigens, leading to poor antibody response (malaria , trypanosomes) Summary Mechanical tissue damage  Immuno-pathology Protein losing enteropathy Metaplastic changes Hypersensitivity & Autoimmunity Anaphylactic Strongyloides, Helminthic infections Hook worms Cytotoxic Tape worms, Trypanosoma cruzi Giardia lamblia Immune complex Malaria Cell mediated immunity Cystoscopy at patient presentation Several ulceration and nodular leishmania lesions on the bladder mucosa due to gross Schistosoma haematuria.  Question In Schistosoma species infection is by which one of the fo;;owing routes? A. Ingestion of eggs with contaminated water B. Drinking of water contaminated with miracidium C. Skin penetration by Cercariae  Concluding Questions Which of the following diseases are transmitted by gastropod vector: a. Malaria b. Schistosomiasis c. Hydatidosis  References Medical Microbiology. Edition by Patrick R. Murray. All Editions Chapters 76, 77