Pathogenesis of Parasitic Infections Flashcards
What are the two main types of leishmaniasis?
β Visceral and Cutaneous
What are the three geographical regions affected by visceral leishmaniasis?
β Asia
β Middle east/africa/asia
β Latin america
What type of visceral leishmaniasis affects Asia?
β Leishmania donovani
What type of visceral leishmaniasis affects the Middle east & Africa?
β L.Infantum variants
What type of visceral leishmaniasis affects Latin America?
β L. Chagasi
What types of cutaneous leishmaniasis affect the new world?
β L.braziliensis/amazonensis/mexicana
What is Leishmaniasis caused by?
β Sand fly
Describe the lifecycle of leishmaniasis?
β The sandfly bites and transmits a promastigote
β The promastigote invades immune cells like macrophages
β Inside the macrophage it forms nests of amastigotes
β the cells eventually burst which release lots of amastigotes and infect other cells which can be taken up by the fly
What is the vector of leishmaniasis?
β Lutzomyia/phlebotomus
In what regions are sandflies common and who do they affect?
β Tropical regions
β people who live in housing of poor standard such as adobe
What type of an infection is leishmaniasis?
β Zoonotic
What is the sylvatic and domestic reservoir of leishmaniasis?
β sylvatic β rodents
β domestic β dogs
Describe the progression of cutaneous leishmaniasis after a bite?
β There is a papule that forms and spreads
β the center becomes necrotic and ulcers form
What happens if you get infected as a child with cutaneous leishmaniasis?
β early immunity to that form of leishmania
When does diffuse cutaneous leishmaniasis occur?
β When there is lack of an immune response to the leishmania
Describe the progression of mucocutaneous leishmaniasis?
β a small proportion of individuals get congested noses
β lesions occur in the mucus membranes
β lesions occur and destroy the nasal septum
When do people get infected with mucocutaneous leishmaniasis?
β as children
What are the three phases of cutaneous leishmaniasis?
β Acute lesions
β Latency
β Relapse (rare)
Describe the pathogenesis of acute lesions in cutaneous leishmaniasis?
β Tissue damage is caused by inflammatory response to the presence of parasites in macrophages
β parasite killing by Th1 proinflammatory responses and macrophage killing
Describe the pathogenesis of the latency phase in cutaneous leishmaniasis?
β regulatory immune response characterised by balance of Th1 and anti-inflammatory responses
β parasites remain present long term
What is a recidivans?
β A recurrence of lesions at the old ulcer site
What is mucocutaneous disease associated with?
β strong but inadequate inflammatory response to parasites that have metastasised to mucosa
What can trigger relapse in leishmaniasis?
β alteration in immune response
What are the three main species of schistosomiasis and what areas of the body do they affect?
β Schistosoma mansoni - hepatic and intestinal
β S. haematobium - urinary system
β S. Japonicum - hepatic
Describe the life cycle of schistosomiasis?
β People become exposed to the infective stage in contaminated water
β they get infected with cercariae
β the cercariae migrate through the body forming adults in the mesenteric system
β schistosoma haematobium forms in the vessels around the bladder
β they form adults, the female releases eggs which are pushed through the mucosal epithelium in the feces or urine which contaminates water and infects snails
How do you get cercarial dermatitis?
β Exposure to cercariae from animal or bird schistosomes
What type of reaction does cercarial dermatitis?
β Allergic type reaction
What happens to the eggs of schistosoma?
β they become organised in granulomas
What leads to organ damage in schistosomiasis?
β Repeated insults and tissue repair lead to fibrosis and organ damage
How does hepato-intestinal schistosomiasis occur?
β Infection with S. mansoni and S.Japonicum
What is pathology caused by in hepato-intestinal schistosomiasis?
β Immune response to the eggs
How does hepato-intestinal schistosomiasis occur?
β The adults are in the mesenteric vessels, the eggs are pushed by the immune response through the intestinal wall and through the mucosa
What happens with chronic exposure during hepato-intestinal schistosomiasis?
β fibrosis in the liver
How do the eggs get into the urine in urinary schistosomiasis?
β adults live in the vessels around the bladder
β they release eggs into the vessels
β the eggs get pushed into the mucosa of the bladder and are excreted in the urine
What is a common sequelae to urinary schistosomiasis?
β there is inflammation in the bladder wall related to the eggs and damage to the bladder wall which leads to cancer
What is a symptoms of urinary schistosomiasis in endemic areas and at what age does this occur?
β haematuria
β adolescence
What is onchocerciasis caused by?
β Filarial parasites
What is onchocerciasis transmitted by?
β black flies
Where is the female worm found in onchocerciasis?
β coiled up in fibrous nodules under the skin
What geographical regions is onchocerciasis found in?
β Equatorial regions of africa and central and south america
Describe the life cycle of onchocerciasis?
β The blackfly bites and transmits infectious larvae
β the larvae migrate under the skin and develop into adults which mate
β the female releases thousands of larvae called microfilariae which are taken up by the blackfly again
What is the vector of onchocerciasis?
β Simulium
Why does permanent scarring occur in onchocerciasis?
β Repeated episodes of inflammation to the presence of microfilariae leads to permanent damage and scarring in the skin and eyes
Why do you give diethylcarbamazine to patients with onchocerciasis?
β The parasite downregulates the immune response
β the downregulation can be switched off by giving diethylcarbamazine
What type of immune response is there to onchocerciasis?
β Strong allergic response with a lot of eosinophils that form eosinophilic abscesses
What 4 skin diseases occur as a result of onchocerciasis?
β Acute papular onchodermatitis
β Chronic onchodermatitis
β with repeated inflammation there is damage to collagen and elastin
β sowda
What 3 anterior segment eye diseases occur as a result of onchocerciasis?
β Punctate keratitis
β acute iridocyclitis
β sclerosing keratitis
What is sclerosing keratitis?
β with repeated inflammation there is opacification of the cornea
What is punctate keratitis?
β little opacities in the cornea
What 2 posterior segment eye diseases occur as a result of onchocerciasis?
β Optic neuritis/atrophy - the retinal vessels are sheathed and there is a pale optic disc
β chorioretinopathy
What is chorioretinopathy?
β small white spots in the eye where microfilariae are being killed
In the acute stage of onchocerciasis what chemokines are produced?
β Strong Th2 response with the production of IL-4 and IL-5
What does IL-4 make?
β IgE
What does IL-5 do?
β Recruits and activates eosinophils
In the chronic stage of onchocerciasis what happens to the immune system and what kind of a response is there?
β there is a modified Th2 response with production of IL-10 and IgG
What 7 diseases do hard ticks cause?
β Tick typhus β viral encephalitis β viral fevers β viral haemorrhagic fevers β tularemia β tick paralysis β human babesiosis
What 2 diseases do soft ticks cause?
β Q fever
β relapsing fever
What is tick paralysis?
β progressive flaccidity due to a failure of AcH liberation in the neuromuscular junction
What 5 types of diseases hard bodied ticks carriers of?
β rickettsial, spirochaetal, viral, bacterial and protozoan diseases
What does a tickβs toxin cause?
β a block in the motor nerve fibres
How are head lice spread?
β close contact, sharing of combs, brushes, hats
What do head lice do?
β’ suck blood from scalp and lay eggs on hair
What do body lice do?
β Suck blood from body and lay eggs on clothing
How are pubic lice different in morphology to body or head lice?
β they are broad and flat with very large stout claws
Describe the lifecycle of the botfly?
β Midflight the fly lays eggs on a mosquito
β the mosquito bites an animal and the egg hatches and larvae migrate into the skin
Why are botflies hard to extract?
β they have spines on the side of their body which anchor into tissue and make them hard to extract
What is orbital cavitary myiasis caused by?
β cochliomyia hominivorax
What 2 drugs are protozoa usually treated with?
β tinidazole
β metronidazole
What is the advantage of tinidazole over metronidazole?
β it has a shorter regimen
What 3 other drugs can protozoa be treated with?
β Nitazoxanide
β Benznidazole
β Heavy metals (meglumine antimoniate)
What is Chagas disease treated with?
β Benznidazole
What is leishmania treated with?
β heavy metals
What 5 drugs are helminths treated with?
β albendazole/mebendazole β praziquantel β ivermectin β diethylcarbamazine β pyrantel
What 2 drugs are ectoparasites treated with?
β Ivermectin
β benzyl/malathion lotions
What is used to treat nematodes such as schistosomiasis?
β praziquantel
How can you control parasite infections by changing behavior?
β Education
β hand washing and hygiene behaviors
How can you control parasite infections by environmental intervention?
β Spraying of residual insecticides for household vectors β mosquito nets for malaria β improved housing β sewage disposal and potable water β drainage of swamps
How are parasite infection in endemic areas treated and why?
β treatment must be given periodically over long periods of time because re-infections are rapid or because the treatment kills larval and not adult stages
What is given to control soil transmitted helminth infections?
β Single dose of albendazole is given to high risk groups such as school children every 4 months
What is given and how often to control onchocerciasis?
β A single dose of ivermectin is given to endemic communities every 6 or 12 months
What is given and how often to control schistosomiasis?
β A single dose of praziquantel is given to endemic communities every 6 or 12 months
