Day 10: Introduction Parasitology, Protozoa and Helminths Flashcards
HC23, 24, 25
HC23: Symbiosis
- Living together
> all organisms have associations
Intraspecies and interspecies association
Intraspecies: associations between animals of same species: herd or flock and parental care
Interspecies: Associations between animals of different species
Interspecies association types
- Mutualism: both benefit: mutually beneficial association between 2 species
- Commensalism: No effect host and benefit of other species: both species can live independent from each other, but one or both may gain advantage from the association
- Parasitism: An organism is living on or in another organism (the host), is dependent on the host and benefits from the association at host’s expense (disadvantage)
Parasite
Maintains and multiplies at expenses of the host with which it lives
Protozoa vs Metazoa
Protozoa: unicellular organisms: Plasmodium, Giardia
Metazoa: multicellular organisms: Schistosoma (worm), Arthropoda (ticks)
Endo vs ectoparasites
- Endoparasites: parasites that live inside their host: intestine, blood tissue and organs: protozoa (unicellular) and helminths (multicellular) (majority is endo)
- Ectoparasites: Parasites that exclusively live of or on the skin of their hosts: Arthropoda: lice, mites, fleas, ticks
biggest and smallest parasites
Biggest: helminths
Smaller: protozao, bacteria and even viruses
Life cycle of parasite requires … from host
Complex interactions between parasite and host
Final (definitive) host
Organism in which the adult parasite is present and where sexual reproduction takes place
Intermediate host
Organism in which the parasite undergoes a specific development where asexual reproduction might occur but not suxual reproduction
Human is not always the final host, name big example
Plasmodium (malaria)
Life cycles:
Direct transmission
- From final host to other final host, no intermediate stages
Life cycles:
Direct life cycle
Final host > free living stage (larval) > final host
- Like Whipworm,: adult worms in intestines of dog > eggs pass in feces > mature eggs ingested by other dog
- Free living larval stage in feces
Indirect life cycle
Final host > Intermediate host (larval) stage > Final host
- But also other combinations: Final host > Intermediate host > Free living stage > Intermediate host 2 > Final host
Schistosoma spp. life cycle
Final host: human
> Adult worms (m/v) paired in blood vessels around intestines
> Sexual reproduction in blood
> Eggs go across endothelium into intestines or bladder
> Excretion eggs through feces or urine
> Eggs go into environmental water
> From eggs a miracidium develops: taken up by snail (intermediate host)
> Asexual reproduction of parasite inside the intermediate host: inside snail sporocysts are made
> Sporocysts develop in snail and are released from snail into water and grow
> Free cerecariae come into contact with human skin and can penetrate (invade) and go into circulation
> Cerecariae lose tails during penetration and become schistosomulae again
Vector
Invertebrate organism that facilitates transmission from one host to another
The snail in the schistosoma spp. life cycle is the …
Intermediate host and the vector
Reservoir
Some parasites occur in both humans as well as in other animals, these animals are called reservoir hosts and are the source of infection for humans: zoonotic infections
> zoonotic infections include reservoir hosts: always
Cryptosporuidium parvum - zoonotic transmission
Cattle: sporulated oocysts pass feces > get into soil > ingestion again via soil
> humans also infected via soil
Life cycle of Cercal dermatitis causing Trichobilharzia ocellata
Common skin disease in summer time
Final hosts: water birds
> eggs passed in feces
> eggs hatch in water and liberate miracidia
> Parasite develops in snail
> cernanae released which penetrate skin of water birds
> accidental: transmission carcanae to humans
Life cycle of Trichobilharzia is a …
Indirect life cycle
Hosts in Trichobilharzia ocellata cycle
Birds: final host (sexual reproduction)
Snail: intermediate host and vector
Human: accidental host
Life cycle Toxoplasma gondii
Cat litter disease: ocular and congenital toxoplasmosis
- Cat is final host
- Fecal oocysts released and passed to mice and birds
- Tissue cysts
- Eaten by cat and infection
- cattle can be infected by cat feces as well
- cat litter can cause disease: pregnant women cannot do this: infection over placenta causes congenital problems in fetus
> Cats and cattle: reservoir
> Direct transmission: from mother to fetus or human to human blood transfusion
> Direct life cycle: cats eat grass which other cat infected
> zoonotic disease: from cat litter or cattle
Health impact parasites
- 2 million people infected
- 25% global mortality
- economic impact via health system: unproductivity, agriculture loss
- social impact
- development: less school days attended and less cognitive development
HC24: Protozao cell
Like eukaryotic cell, but may lack some familiar organelles like mitochondria and Golgi apparatus in Giardia
Cryptosporidium
Intestine parasite causing diarrhea, immunocompromised host affected, zoonotic infections possible
Trypanosoma characteristics
Blood and brain affected, immune evasion, lack of medicines
Cryptosporidium spp. life cycle
Oocysts with feces excretion from intestines
> C. parvum major host: cattle, humans via zoonotic infection
> C. hominis: infection of humans > contamination water and food with oocysts > thick walled oocyst ingested by host: go into GI tract
> asexual and sexual cycles in human
Specific locatalization of Cryptosporidium spp. in human
Wall of the small intestine
Absorbing nutrients and Cryptosporidium infection
Is imparied because diarrhea and mucus and epithelium affected
> severe diarrheal disease: risk for children, eldery, immunocompromised > dehydration
Transmission type of Cryptosporidium
Fecal-oral route with contaminated water
Oocysts are very …
resistant
Therapy Cryptosporidium
Paramomycin, for the immunocompromised
Infection Cryptosporidium treatment normally
Should disappear spontaneously in immunocompetent
Diagnosis Cryptosporidium
Microscopy: Staining methods
> difficult morphology: confusion with yeast
> PCR
Symptoms Cryptosporidium
- Diarrhea: das to weeks and often watery-loose
- Fever often present
Symptoms Cryptosporidium in immunodeficient persons / AIDS
- Persistent infectin (low CD4)
- Diarrhea, frequent water, sometimes liters per day
- Anorexia, nausea, sometimes vomiting
- Pain in right upper quadrant abdomen
» Cryptosporidiosis is life threatening in AIDS
Most common protozoan GI infection worldwide
Cryptosporodiosis
Milwaukee outbreak
Contaminated tap water with Cryptosporidium
> resistant oocysts against water-treatment-plant
Diarrheal disease in Malawi
Large part by Cryptosporidium or Giardia (almost no co-infection)
> No infections in domestic animals
> Main source oocysts are soil and toilets
- Antroponotic transmission: human to huma
- wash measures
Human African Trypanosomiasis (HAT)
Sleeping disease
> by T. brucei
» by T. b. gambiense: Gambian HAT (chronic form, West Africa)
» by T. b. rhodesiense: Rhodesian HAT (acute form, East Africa)
Kinetaplasts of Trypanosoma
Have next to nucleus, second organelle with mtDNA for energy management
Life cycle African Trypanosoma
Tsetse fly: blood sucking fly
Indirect life cycle with the vector: tsetse fly
> zoonotic reservoir: cattle
> there are subtypes which infect cattle specifically
Transmission Trypanosoma brunei: reservoir
- Wild and domestic animals reservoir for t. b. rhodesiense
- Infected humans reservoir for t. b. gambiense
» fertile regions affected: green desert
Stage 1 HAT symptoms
- Recurrent fever ddx (differential diagnosis) incl malaria, HIV, brucellosis
Lymphadenopathy - ddx tuberculosis, HIV and cancer
Do the trypanosoma have intracullar stages
No
Stage 2 (late) HAT symptoms
Mental status change
ddx tuberculosis, meningitis and HIV-related opportunistic infections
Sleeping
HAT has been sometimes seen as witchcraft (evil spirits) resulting in..
More visits of spiritual healers instead of meds
Diagnosis HAT
Spinal fluid sample
Problem with HAT treatment
- Few old drugs
- Treatment depends on stage disease
- Drugs that are efficient in treatment of HAT in early stage are not effective in late stage
- Treatment success in late stage is low, relapse in common
Stage 2 HAT treatment: Melarsoprol
- Drug of choice: can pass blood brain barrier
- Painful treatment: deaths and relapses occur
- Toxic, causes myocarditis, renal damage and encephalopathy
- Resistance occurs
Eflornithine and Nifurtimox
Possible treatments for stage 2 HAT which are not used because patent on it
Compromised eradication of HAT
Pandemic COVID and civil wars
Evasion host immune system by Trypanosoma
Lives in blood > hostile environment: immune system
» Fluctuations in parasitemia during infection
> Variant surface glycoproteins (VSGs) of Trypanosoma are essential for survival
> switch genes on or off to vary the surface glycoproteins
> VSG: protein which densely packs cell surface of parasite
» no biochemical activity
» protect against host environment and immune responses
» waves of VSG variants during chronic infection based on selective pressure
HC25: Helminths classes
- Trematoda: flukes
- Cestoda: tape worms
- Nematoda: round worms
Helminths
Large worms, visible with the eye and composed of many specialized cells
Specialized cells and organs of helminths and properties
- Brain with neuropeptides
- Digestive system
- Reproductive system
- Parasite - parasite communication
- Parasite - host communication
- Females are larger than males
- can survive for long time
Nematodes, trematodes examples
- Nematodes: ascatis, hookworm, onchocerca
- Trematodes: schistosoma
- Guinea worm
Nematodes character
- Huge numbers
- Huge biomass
- Huge impact
- Soil-transmitted helminths: adult worms of greatest public health significance
Burden of ascaris worms
Can become up to 40 cm, in intestine
Ascaris worm life cycle
In GI tract > lay eggs
> fertilized eggs in feces
> consumption via soil
> worms to intestine
> larvae can be coughed up via lungs for re-infection
Hookworm cycle
Hooks to intestinal wall with hooks and suck blood
> causes anemia in children at risk
> larvae exit circulation in lungs > coughed up and swallowed
> eggs in feces
> larvae develop in environment (in warm, moist soil: this limits the distribution to certain climatic conditions) and penetrate skin at foot
Onchocerciasis
Causes river blindness
O. valvulus
> vector: black fly
> adult worms in skin nodules
> migrating microfilariae causing severe itching: Leopard skin
> Treatment with Ivermectin > only treats the larvae: larvalcidal (but why take pills when you are not sick (still larvae): problem
> nodes with parasites removed through surgery
Life cycle Onchocerciasis valvalus
in skin nodules
> blackfly takes blood meal
> larval stages in fly
> infection by the fly
> worms go to subcutaneous tissues
Schistosomiasis
Parasitic disease caused by Schistosome worms
> five species cause human disease
> second most prevalent parasitic disease
> a neglected tropical disease (NTD)
> Schistosoma mansoni the most important
Life cycle of Schistosoma spp.
Final host human
> schistosomulae in circulation
> adult worms lay eggs
> miracidia in feces
> snails as intermediate host
> formation sporocysts
> formation cercaria which leave and penetrate human skin
Clinical signs Schistosomiasis
- Cercarial rash when first infection
- Goes into blood afterwards
> acute schistosomiasis
> Katayama syndrome: immune complexes deposited in tissues - Chronic: into blood vessels around intestine and bladder
> chronic schistosomiasis
> granuloma formation in tissues
> urinate blood
Intestinal schistosomiasis
S. japonicum, S. mansoni and others
> eggs trapped in different tissues like liver
> granulamatous reaction
> fibrosis of liver
Urinary schistosomiasis
S. haematobium
> eggs trapped in different tissues like bladder
> granulamatous reaction
> fibrosis of the bladder
Dracunculiasis
Guinea worm disease
> eradiacation almost
> females when full of eggs > migrate to the foot and cause large blisters
> For relief, humans put foot in water
> Larvae released into water from emerging female worm which creeps out the blister of the foot and releases eggs
> large worm
> reproduce in subcutaneous tissues
Life cycle Guinea worm
In human > reproduce in GI tract
> fertilized female worm migrates to surface skin in foot and causes blister and releases and releases larvae into water
> larvae develop in water
> larvae consumed by copepod in water
> infected copepods in unfiltered drinking water or eaten via larger fish
Treatment Guinea worm
No vaccine, no treatment, no immunity
> try to facilitate safe water access: interrupt transmission
> active case detection and containment
> heightened surveillance
> education awareness
