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Parasitology

Dr Sarah Cliffford Specialist Registrar in Infectious Diseases and General

Medicine

10min

November 2020

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LEARNING OBJECTIVES

DEFINITION EPIDEMIOLOGYMICROBIOLOGY

PATHOLOGYDIAGNOSIS COMPLICATIONS MANAGEMENT

TAKE HOME MESSAGES

REFERENCES

Learning Objectives

1. Definitions of parasitic agents

2. Classification

3. Life cycles

•Toxoplasmosis

•Strongyloides

•Schistosomiasis

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} Diagnosis, complications and treatment

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Definitions

Parasites

“A parasite is an organism that lives on or in a host organism and gets its food from or at the expense of the host”

CDC

There are three main classes of parasites that can cause disease in humans:

1. Protozoa

2. Helminths

3. Ectoparasites

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1. Protozoa-microscopic, one celled organisms ( free living or parasitic)

• Classified into four groups based on their movement:

1. Sarcodina ( the amoeba e.g Entamoeba histolytica)

2. Mastigopohora ( the flagellates e.g Giardia)

3. Ciliophora (the ciliates e.g. Balantidium)

4. Sporozoa ( adult stage non motile e.g Plasmodium)

2. Helminths- Large multicellular organisms that are generally visible to the naked eye in their adult stages

• Three main groups that are human parasites:

1. Flatworms (platyhelminths) includes trematodes (flukes) and cestodes (tapeworms)

2. Thorny-headed worms (Acanthocephalins) *rarely cause human infections and not covered in this presentation

3. Roundworms (nematodes)

3. Ectoparasites (ticks, fleas, lice and mites) Organisms which attach to the skin and remain there for a period of time to obtain nutrients


PATHOLOGYLEARNING

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Organism (Protozoa) Geographical Distribution

Babesia spp North America, Europe

Cryptosporidium spp Worldwide

Entamoeba histolytica Worldwide

Giardia duodenalis Worldwide

Leishmania spp Dependant on species

L. donovani- India Paistan, East africa and china

L. Viannia braziliensis- Latin America

Naegleria spp Worldwide

Plasmodium spp Dependant on species

Tropical and subtropical areas and altitudes below 1,500 m

P. falciparum- predominant species in the world

P. vivax (Asia and Africa (absent from West Africa))

P. ovale (Sub Saharan Africa)

P. malariae (wide global distribution, being found in South America, Asia, and Africa)

P. knowlesi –Southeast Asia

Toxoplasma gondii Worldwide

Trypanosoma spp T. cruzi – South and Central America

T. brucei gambuense- West Africa

T. brucei rhodesiense- East Africa

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Organism (Helminths) Geographical distribution

Flat Worms

Flukes (Trematodes)

Liver

• Faciola Hepatica

• Faciola Gigantica

• Opisthorcis

• Clonorchis

Endemic in many countries worldwide:

• Faciola Hepatica (focal areas in all continents except Antartica)

• Faciola Gigantica (Africa, Asia and Hawaii)

• Opisthorcis (Thailand, Laos, Cambodia, Vietnam, Germany, Italy, Belarus, Russia, Kazakhstan, and Ukraine)

• Clonorchis (parts of Asia)

Gut

• Fasciolopsis buski

• Echinostoma species

• Heterophyes

• Metagonimus species

Endemic in many countries worldwide

Tissue

• Paragonimus (lung)

Areas of Africa and South America but predominantly found in Asia

Blood

Schistosomiasis

• S. mansoni

• S. haematobium

• S. japonicum

S. mansoni ( Africa, South America (brazil, Suriname and Venezuela) Caribean present but low risk)

S. haematobium ( Africa, Middle East, Corsica)

S. japonicum ( Indonesia and parts of china and Southeast Asia)

Cestodes (Tapeworms)

• Dwarf (Hymenolepsis nana)

• Fish (Diphyllobothrium datum)

• Beef (Taenia saginata)

• Pork (Taenia solium)

• Hydatid (Echinococcus granulosus/ E. multiocularis)

• H. nana (Mediterranean countries)

• D. latum (Countries where fish is eaten raw)

• T. saginata (Eastern Europe, Russia, Eastern Africa and Latin America)

• T. solium (South America, Africa, Asia)

• E. granulosus (Sheep farming areas global distribution)

• E. multiocularis (Northern USA, Northern Europe and Asia)

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Organism (Helminths) Geographical Distribution

Nematodes Geohelminths Ascaris lumbracoides Global distribution. Most cases in tropical and subtropical areas of Asia sub-Saharan Africa and the Americas

Trichinella Trichinella spiralis has a global distribution

Enterobius Global distribution

Trichuris Tropical climates globally ( Regions with poor sanitation)

Hookworms

• Ancylostoma duodenale

• Necator americanus

Ancylostoma duodenale and Necator americanus, are worldwide in areas with warm, moist climates

Strongyloides All continents except for Antarctica. Most common in the tropics, subtropics, and warm temperate regions

Toxocara Toxocara most prevalent in hot humid regions

Filariae Mansonella species West, East, and Central Africa, and is also highly prevalent in some neotropical regions of Central and South America

Lymphatic filariasis

• Wuchereria bancrofti

• Brugia malayi and Brugia timori

• Wuchereria bancrofti:Asia, Africa, the Western Pacific, and parts of the Caribbean and South America

• Brugia malayi and Brugia timori: Asia

Loa loa Rain forests in West and Central Africa

Onchocerca Sub- Saharan Africa, South America, Yemen and Middle East

Dracunculus Poor communities in remote parts of Africa that do not have safe water to drink

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Organism (Ectoparasites) Geographical Distribution

Lice Diseases

• Epidemic typhus (Rickettsia prowazekii)

• Trench fever ( Bartonella quintana)

• Louse-borne relapsing fever (Borrelia recurrentis)

• Louse-borne epidemic typhus: African highlands, Iraq, Afghanistan, Andes and Central America)

• Trench Fever- areas of overcrowding and poor hygiene

• Louse-borne relapsing fever (Ethiopia, Sudan, Afghanistan)

Fleas Diseases

• Plague (Yersinia pestis)

• Endemic Typhus (Rickettsia typhi)

• Jigger Fleas (Tunga Penetrans)

• Plague: Uganda, Algeria, Mongolia, Madagascar, New Mexico

• Endemic Typhus: Worldwide

• Jigger Fleas: tropical and subtropical regions of the world, including Mexico to South America, the West Indies and Africa

Mites Diseases

• Scabies (Scarcoptes scabiei)

Worldwide

Ticks Hard Ticks Rickettsiae-Tick typhus (spotted fevers)

Q fever (Coxiella burnettii)

Arboviruses

Tularaemia (Francisella tularensis)

Tick paralysis

• Rickettsiae rickettsii- Western hemisphere, Rickettsia conorii- Mediterranean, Africa, India, South west Asia)

• Q fever ( US and Australia)

• Tularaemia ( United States except Hawaii)

Soft Ticks • Tick-borne relapsing fever (Borrelia duttoni) North America, plateau regions of Mexico, Central and South America, the Mediterranean, Central Asia, and much of Africa

Images courtesy of the Centers for Disease control and Prevention CDC

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Toxoplasmosis

LEARNING OBJECTIVES

DEFINITIONMICROBIOLOGY


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REFERENCESEPIDEMIOLOGY

1.Unsporulated oocysts are shed in the cat’s feces2.Oocysts take 1–5 days to sporulate in the environment and become infective. Intermediate hosts in nature become infected after ingesting material contaminated with oocysts3.Oocysts transform into tachyzoites shortly after ingestion. These tachyzoites localize in neural and muscle tissue and develop into tissue cyst bradyzoites4.Cats become infected after consuming intermediate hosts harboring tissue cysts 5.Cats may also become infected directly by ingestion of sporulated oocysts. Animals may also become infected with tissue cysts after ingestion of sporulated oocysts in the environment

Humans can become infected by any of several routes6.Eating undercooked meat of animals harboring tissue cysts7.Consuming food or water contaminated with cat feces or by contaminated environmental samples8.Blood transfusion or organ transplantation9.Transplacentally from mother to fetus10.In the human host, the parasites form tissue cysts 9


Toxoplasmosis

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Now draw the lifecycle from memory you will be tested on the steps of the cycle later

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Toxoplasmosis

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1. _______ are shed in the cat’s faeces2.Oocysts take 1–5 days to sporulate in the environment and become infective. Intermediate hosts in nature become infected after ingesting material contaminated with oocysts3.Oocysts transform into _______shortly after ingestion. These ________localize in neural and muscle tissue and develop into tissue cyst ________4.Cats become infected after consuming intermediate hosts harboring tissue cysts 5.Cats may also become infected directly by ingestion of sporulated oocysts. Animals may also become infected with tissue cysts after ingestion of sporulated oocysts in the environment

Humans can become infected by any of several routes6.Eating undercooked meat of animals harboring tissue cysts7.Consuming food or water contaminated with cat feces or by contaminated environmental samples8.Blood transfusion or organ transplantation9.Transplacentally from mother to fetus10.In the human host, the parasites form tissue cysts

Fill in the blanks

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Toxoplasmosis

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1.Unsporulated oocysts are shed in the cat’s feces2.Oocysts take 1–5 days to sporulate in the environment and become infective. Intermediate hosts in nature become infected after ingesting material contaminated with oocysts3.Oocysts transform into tachyzoites shortly after ingestion. These tachyzoiteslocalize in neural and muscle tissue and develop into tissue cyst bradyzoites4.Cats become infected after consuming intermediate hosts harboring tissue cysts 5.Cats may also become infected directly by ingestion of sporulated oocysts. Animals may also become infected with tissue cysts after ingestion of sporulated oocysts in the environment

Humans can become infected by any of several routes6.Eating undercooked meat of animals harboring tissue cysts7.Consuming food or water contaminated with cat feces or by contaminated environmental samples8.Blood transfusion or organ transplantation9.Transplacentally from mother to fetus10.In the human host, the parasites form tissue cysts 12


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13Images courtesy of the Centers for Disease control and Prevention CDC

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Images courtesy of the Centers for Disease control and Prevention CDC19

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Images courtesy of the Centers for Disease control and Prevention CDC20

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Toxoplasmosis

1. Serology (Only reliable in immunocompetent)

• IgG- gradually rises over time. Avidity increases over time

• IgA- more sensitive than IgM in congenitally infected babies

2. Polymerase Chain Reaction (PCR) May help diagnosis of intracerebral infection or CSF in immunocompromised (low sensitivity)

Schistosomiasis

1. Ultrasound (liver/bladder)- characteristic appearances

2. Stool concentration techniques to identify eggs

3. Urine

• Dipstick- blood

• Filtration and sedimentation-egg identification

4. Blood

• Acute stage-eosinophilia

• IgG ( does not distinguish between active and past infection

Strongyloides

1. Repeated stool microscopy

2. Serology21

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Spot Diagnosis


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Spot Diagnosis- Answers

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S. mansoni

S. haematobium

S. japonicum

Strongyloides stercoralis larvae

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Toxoplasmosis• Usually asymptomatic in immunocompetent host (can cause rash, fever and

painless cervical lymphadenopathy) • Congenital Toxoplasmosis ( if acquired early in pregnancy) • Ocular In the immunocompromised • HIV- when CD4 count <100 ( CNS disease, ring enhancing lesions)• Transplant ( Life threatening, fever, confusion and respiratory failure)

Schistosomiasis

• Acute - Katayama fever: acute illness with fever, eosinophilia +/_ pneumonitis• Haematobium- Obstructive uropathy, Squamous bladder cancer, infertility,

Pulmonary granulomas• Mansoni/Japonicum- Portal hypertension, Liver fibrosis • CNS involvement (ectopic worms) meningoencephalitis and seizures

Strongyloides• Acute infection- itchy rash, Lofflers-like pneumonitis, diarrhoea • Skin- larva current • Chronic- weight loss, abdominal pain, malabsorption• Hyperinfection in the immunocompromised

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Toxoplasmosis

Pyrimethamine and Sulfadiazine is first line- dose and duration dependant on clinical syndrome

NB Treatment of immunocompetent adults with lymphadenopathictoxoplasmosis is rarely indicated; this form of the disease is usually self-limited

Schistosomiasis

Praziquantel (dose dependant species) mainly effective on adult worms so travellers need to wait at least 6-8 weeks after last exposure to potentially contaminated freshwater

Strongyloides

Ivermectin ( oral for two days) prolonged or repeated treatment may be required in some cases

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Remember your epidemiology it is essential for making a diagnosis.

Learn the lifecycles they will help you to identify those at risk and inform them how they probably acquired the infection.

Diagnosis of acute infection can be difficult and requires the history (exposure) and clinical features alongside the investigations(Sometimes tests are misleading)

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REFERENCES

Tropical Medicine Notebook. P. Matthews. Oxford University Press 2017

Mandell Douglas and Bennetts Principles and Practice of Infectious Diseases by Bennett & John E.Doli. 9th Edition

For information on the malaria risk by country use the following link

https://www.cdc.gov/malaria/travelers/country_table/a.html

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https://www.cdc.gov

https://www.cdc.gov/malaria/travelers/country_table/a.html

https://www.cdc.gov/

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