The significance of Medical Parasitology

The significance of Medical Parasitology Prevalent infections worldwide Significant morbidity & mortality Significant impact on economic & social development Increased mobility of individuals & populations Drug resistance, climate change & opportunistic infections

Global estimates of parasitic diseases and disease burden (Topley & Wilson, 2005)

Definitions of parasitism Concept of metabolic dependence (Smyth) (nutrition, developmental stimuli, control of maturation) Genetic complementation Population dynamic approach (Crofton)- lethal level, overdispersion, reproductive rate

Parasitic adaptations Morphological adaptations Biochemical changes Specialized mechanisms for entry Complex life cycles and transmission opportunities Mechanisms for immune evasion Impact on host versus impact of host

Parasitic adaptations

Important parasitic groups Microparasites (Protozoa) Kinetoplastida Ciliophora Apicomplexa Macroparasites (Helminths, Arthropods) Platyhelminthes Nematoda Arthropoda

Important issues associated with parasites of human importance Life cycle and transmission Pathology and symptomatology Epidemiology, human behaviour and at risk groups Medical history Diagnostic difficulties Prevention and control

Approach to the patient Full history required particularly travel history Symptoms may be subtle and may change over time (repeated history taking) General history also important - occupation, hobby and leisure activities, diet, drugs taken. Clinical exam

Life cycle and routes of transmission Diverse routes of transmission which relate to human behaviour and risk factors e.g. Toxoplasma gondii Diverse routes of transmission with implications for parasite survival and pathogenicity e.g. Strongloides stercoralis

Toxoplasma Life cycle

Strongyloides life cycle

Symptomatology and pathology 1 Parasites often provoke nonspecific and diverse symptoms e.g. Toxocariasis in children Microparasites often provoke more acute disease compared to the chronicity of macroparasites e.g. Plasmodium falciparum versus Strongyloides stercoralis in returned travellers

Symptomatology and pathology 2 Differential pathology Immunocompromised versus Immunocompetent hosts e.g. Toxoplasma gondii & Cryptosporidium parvum

Epidemiology Changes in human behaviour At risk groups Migration and International travel Exotic foods Pet ownership (including exotic pets) Intensification of agricultural practices At risk groups Age, Occupation, Immune status, Pregnancy, Organ transplantation

Diagnostic dilemmas Different diagnostic tests for different patient groups Toxoplasma gondii Need for repeat diagnostic testing Giardia intestinalis Need for improved sensitivity of diagnostic methods Strongyloides stercoralis & Taenia solium

Prevention and control

Dracunculus medinensis : guinea worm

Prevalence of important Microparasites Malaria : 500 million (annual deaths 2.2 to 2.5 million) Giardiasis : 200 million American Trypanosomiasis : 16-18 million (annual deaths 60,000) Leishmaniasis : 12-13 million Amoebiasis : 500 million

Prevalence of important Macroparasites Cestodiasis : 70 million Schistosomiasis : 200 million (annual deaths 500,000 to 1 million) Lymphatic filariasis : 78.6-90 million Onchocerciasis : 17.5 million Ascariasis : 1.3 billion Hookworm : 1 billion Strongyloidiasis : 80-100 million

The Big Three and Neglected tropical diseases (NTDC) Three vector-borne protozoa: Leishmaniasis, African Trypanosomiasis & Chagas disease Three bacterial infections: trachoma, leprosy and Buruli ulcer Seven helminth infections: hookworm, ascariasis, trichuriasis, lymphatic filariasis, onchocerciasis, guinea worm & schistosomiasis Cysticercosis, food-borne trematodiasis & some other parasitic infections could be included From Hotez et al, 2006, PLoS Medicine

Implications of co-infections

Challenges Rare diseases Echinococcus multilocularis : alveolar echinococcosis (AE) Emerging diseases

Toxoplasmosis Malaria Schistosomiasis Neurocysticercosis Lymphatic filariasis

Texts Topley and Wilson’s Microbiology and Microbial infections Parasitology (2005). Eds Cox, F.E.G., Wakelin, D., Gillespie, S.H and D.D. Despommier. 10th Edition. Hodder Arnold. Peters, W. and Pasvol, G. (2007). Tropical Medicine and Parasitology. Mosby 6th edition.