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What causes visceral parasitic infections?
amoebae, ciliates and coccidia
Give examples of flagellate coccidia
Giardia and Trichomonas
Give examples of apicomplexa coccidia
cryptosporidium and toxoplasma
What is Entamoeba histolytica?
anaerobic protist which causes amoebiasis
How is E. histolytica transmitted to humans?
through contaminated water and food
cysts produced by infective form of E. histolytica
resistant to gastric acids
excystation produces 8 trophozoites per cyst in small intestine
amoebiasis symptoms
asymptomatic or diarrhoea and/or dysentery
What happens if amoebiasis is left untreated?
E. histolytica may invade liver and in 10% of cases, the lungs and brain
how is amoebiasis diagnosed?
cysts in stool observed by microscopy
amoebiasis treatment
Azoles, particularly metronidazole. Paromomycin or iodoquinol used for luminal amoebiasis
How does metronidazole work?
Pyruvate:ferredoxin oxidoreductase (POR) reduces metronidazole to its active form, producing covalent protein and DNA adducts → parasite death
reduction of metronidazole nitro groups
produces nitroso- intermediates which covalently bind DNA, disrupting helical structure, inducing strand breaks and inhibiting nucleic acid synthesis → cell death
iodoquinol
iron chelator not taken up by intestinal cells
What is Balantidium coli?
Ciliated intestinal parasite of humans and swine
How is B. coli transmitted to humans?
via faecally contaminated water. Infection caused by cysts
diagnosis of B. coli
occurs from microscopy of stools and colon tissue
B. coli treatment
tetracycline, metronidazole and iodoquinol
Why is tetracycline used to treat B. coli?
it may inhibit protein synthesis by binding mitochondrial ribosomes
What happens when B. coli cysts are ingested?
The cysts form trophozoites which multiply. Some invade the colon wall. Cysts and trophozoites are then excreted
Giardia intestinalis
Flagellated anaerobic parasite which produces highly resistant cysts and causes giardiasis
Giardia intestinalis contains mitosomes. What are mitosomes?
mitochondrial remnant organelles not reliant on the electron transport chain.
giardiasis symptoms
explosive foul-smelling diarrhoea, intestinal cramps, nausea, weight loss and malaise. Some people are asymptomatic carriers
How is giardiasis diagnosed?
via cysts and trophozoites in faeces
How is giardiasis treated?
metronidazole and tinidazole
What happens after infective G. intestinalis cysts are ingested?
They remain in the intestine and form trophozoites. Cysts and trophozoites are excreted but trophozoites don’t survive the environment
What is Trichomonas vaginalis?
Sexually transmitted, flagellated anaerobic parasite. Survives on moist surfaces so can be transmitted by toilet seats, sauna benches and towels
T. vaginalis symptoms
asymptomatic in males. Causes purulent vaginal discharge, itching and burning in women
T. vaginalis diagnosis
microscopy and cell culture from patient secretions
T. vaginalis treatment
metronidazole
T. vaginalis trophozoites
in vaginal and prostatic secretions as well as urine. Multiply by binary fission and colonise vagina/urethra orifice
Cryptosporidium parvum
Apicomplexan parasite of warm-blooded animals which produces thick-walled cells known as oocysts
How is C. parvum transmitted?
oocysts are shed in infected faeces and transmitted in faecally contaminated water
How are C. parvum oocysts removed from infected water?
Oocysts resistant to chlorine and filtration so sedimentation and filtration methods most effective
Where does the C. parvum parasite develop?
just under epithelial cell membrane in an intracellular, extracytoplasmic position
C. parvum diagnosis
direct fluorescence antibody assay of a stool sample
C. parvum treatment
infection self limited but can be treated with nitazoxanide (interferes with anaerobic energy metabolism)
C. parvum sporozoites
sporozoites develop into trophozoites inside oocysyts
asexual C. parvum trophozoite cycle
trophozoite → type I meront → merozoite → trophozoite
What happens when C. parvum merozoites leave the asexual cycle?
develop into type II meronts which then form merozoites in a sexual cycle
undifferentiated gamonts in the C. parvum cycle
form micro and macrogamonts, allowing zygotes to form which produce thin and thick walled oocysts
thick walled C. parvum oocysts
exit by excretion to infect someone else
thin walled C. parvum oocysts
remain in the intestine
Toxoplasma gondii
Apicomplexan protist parasite of warm blooded animals with similar life cycle to C. parvum
transmission of T. gondii
cats and undercooked meat
toxoplasma symptoms
asymptomatic but causes eye, brain and organ damage in immunocompromised individuals
What happens if a pregnant mother is infected with Toxoplasma?
may cause birth defects eg hydrocephalus
Toxoplasma treatment
Sulphadiazine and Pyrimethamine
Naegleria fowleri
Free-living amoeba found in soil and water
N. fowleri transmission
swimming in warm, soil-contaminated water eg hot springs or lakes. Enters via nose and burrows directly into the brain
N. fowleri symptoms
extensive brain haemorrhage and damage (meningoencephalitis). Usually fatal
N. fowleri diagnosis
from cerebrospinal fluid
N. fowleri treatment (only effective if diagnosed early)
Azoles, amphotericin B, rifampicin and miltefosine
Acanthamoeba
eg castellani, polyphage and culburtsoni. Found in fresh and salt water
How do Acanthamoeba cause infection?
via contaminated contact lenses or contact lens cases. Can also infect broken skin
Acanthamoeba keratitis (AK)
eye disease caused by Acanthamoeba
cutaneous Amoebiasis
skin disease caused by Acanthamoeba
Acanthamoeba diagnosis
microscopic examination of tissue samples
two forms of Acanthamoeba
favourable conditions = active trophozoite
non-favourable conditions = non-dividing, resistant cysts
Acanthamoeba keratitis treatment
Not always successful, usually needs corneal transplant although reactivation can happen
Plasmodium life cycle in mosquitoes
sporogenic
Plasmodium life cycle in humans
liver = exo-erythrocytic
blood = erythrocytic
How is malaria diagnosed?
microscope identification of Plasmodium-infected erythrocytes in blood smears. May appear as trophozoite rings, gametocytes or schizonts
prevention and treatment of malaria using drugs
chloroquine and mefloquine (Lariam), pyrimethamine, doxycycline and clindamycin
Plasmodium
Apicomplexan parasite causing malaria. Uses Anopholes mosquitoes as vectors
What are the 5 species of Plasmodium able to infect humans?
P. malariae, P. vivax, P. ovale, P. falciparum and P. knowlesi
Trypanosomatids
Cause blood and tissue parasitic infections
What is leishmania?
flagellated protozoan
How is Leishmania transmitted and what cells does it infect?
transmitted by sandfly bites. Infects and grows in macrophages
How is leishmaniasis diagnosed?
tissue microscopy, PCR and serology
Leishmania life cycle in sandflies
sandfly ingests amastigote-infected macrophages
amastigote → promastigote in midgut
promastigotes divide and migrate to proboscis
sandfly bites human
Leishmania life cycle in humans
promastigotes phagocytosed
pro → amastigotes in macrophages
amastigotes multiply in various tissues inc macrophages
Leishmania mexicana
causes cutaneous leishmaniasis → skin nodules and ulcers
leishmaniasis treatment
pentavalent antimonial compounds (toxic), amphotericin B (expensive) and miltefosine
Leishmania braziliensis
mucocutaneous leishmaniasis → destruction of mouth, nose and throat mucosa and cartilage
Leishmania donovani
visceral leishmaniasis → liver, spleen and bone marrow damage
post-kala-azar dermal leishmanoid (PKDL)
VL relapse due to incomplete destruction of L. donovani
subspecies of Trypanosoma brucei
T. brucei gambiense and T. brucei rhodesiense - latter more severe
Trypanosoma brucei
causes African sleeping sickness
how is African sleeping sickness transmitted?
tsetse fly bite
stage I African sleeping sickness
intermittent fever
Stage II sleeping sickness
parasites cross blood-brain barrier → brain tissue inflammation and necrosis
stage II sleeping sickness diagnosis
spinal puncture and microscopy of cerebrospinal fluid
The meningoencephalitic stage of sleeping sickness is where the CNS is invaded. What are the symptoms?
headaches, somnolence, abnormal behaviour, lethargy, loss of consciousness and coma
African sleeping sickness treatment
suramin, melarsoprol, pentamidine and eflornithine
T. brucei life cycle in the Tsetse fly
fly ingests trypomastigotes
trypomastigotes → procyclic in midgut, divide by binary fission
procylic trypomastigotes → epimastigotes
epi multiply in salivary gland and become metacyclic
fly bites human
T. brucei life cycle in humans
trypomastigotes transformed and carried to other sites via blood
multiply by binary fission in blood, lymph and spinal fluid
Trypanosoma cruzi
causes Chagas’ disease aka American trypanosomiasis
transmission of T. cruzi
bite and defecation of the Triatomine bug
Chagas diagnosis
microscopy/serology
Chagas treatment
nifurtimox (Lampit) and benznidazole (Radanil)
What organs does T. cruzi affect?
heart, GI tract and CNS
T. cruzi life cycle in triatomine bug
bug ingests trypomastigotes
trypomastigotes → epimastigotes in midgut
transform to metacyclic trypomastigotes in hindgut
bites human and passes metacyclic trypomastigotes in faeces which enter the wound
T. cruzi life cycle in humans
trypomastigotes penetrate cells at bite wound
transform → amastigotes inside cells
amastigotes multiply by binary fission
transform → trypomastigotes, burst from cell and enter bloodstream
infect other cells and cycle continues