parasitic infections Flashcards
what are the Main Anti-protozoal Drugs
examples of each
Toxoplasmosis: pyrimethamine, sulphadiazine, clindamycin, clarith/ azithromycin
Anti-amoebics: Tinidazole, metronidazole, diloxanide furoate
Anti-malarials: chloroquine, proguanil, atovaquone, artemisinins, doxycycline
what are parasites?
Living organism requiring intimate prolonged contact with another living organism to meet some of its basic nutritional needs
organisms of varying complexity from unicellular protozoa to complex multicellular helminths
what are examples of endo parasites and ectoparasites
Endoparasites
Protozoa
Helminths
Ectoparasites
Lice
Leeches
Scabies
Fleas
what is Protozoa
Unicellular eukaryotic organisms
Means “first animal”
Feed on bacteria and particles of nutrients
during growing stage
~20,000 different species but relatively few cause disease
Diverse structure, most inhabit water/soil
Some use insect vectors, others environment (e.g. water-borne)
Important for travel medicine as many infections from tropics
what are protozoal infections
Protozoal Infections include:
Malaria (top right image)
Intestinal infections – Amoebic dysentery, toxoplasmosis and cryptosporidiosis
what are the causes of malaria
how is it transmitted
what are the main 4 types
diagnosis
symtpoms
preventions
treatment
Cause: parasitic protozoa “Plasmodium”
Infects human and insect (mosquito) hosts alternately
Latest data are 2020, 241 million cases, mostly in Africa and mostly P. falciparum
627,000 deaths, more than two-thirds in <5yrs
UK cases are imported: 1719 in 2019, mainly P. falciparum
4 main types: P. falciparum, P. vivax, P. ovale and P. malariae
Most important types: P. falciparum most common in Africa and e.g. eastern Mediterranean with P. vivax common in South East Asia & Americas
P. falciparum is considered most serious (e.g. cerebral malaria)
Other types typically give less severe disease
P. vivax and ovale can lay dormant in liver – relapse
Diagnosis: usually blood film microscopy and/or antigen-based rapid diagnostic tests (RDT)
SYMPTOMS
For uncomplicated malaria, commonly have a mix of:
Fever, chills, headaches, sweating, nausea, vomiting, aches and general feeling unwell
May have bouts of shivering, fever and sweats that occur for a few hours every 3 or 4 days but less common
More severe malaria is an emergency and can include a range of serious effects such as cerebral malaria and other organ and metabolic damage
PREVENTION
-anti-marial drugs
mosquito nets
covering
permethrin
TREATMENT
Vaccines
1. RTS,S (P. falciparum) – blocks liver infection
Work began in late 1987
Clinical trials in children and infants, including large Phase III 2009-14
39% & 29% decrease malaria & severe malaria cases (respectively) 5-17mo old
July 2015 EMA approval (MOSQUIRIX)
Pilot in Ghana, Kenya, Malawi>800,000 children since 2019
Recommended by WHO on 6th Oct 2021 for more widespread use
- R21 (P. falciparum)
Recent trial in ~450 showed ~80% effectiveness
Larger trial currently underway
Both protein-based vaccines with adjuvant
Recent trial showed combining vaccine + chemoprevention effective reducing incidence, severe malaria and death
Malaria transmissionand life-cycle
Human Stages:
Mosquito bites / feeds, injects sporozoites
Infect liver cells
Develop to schizont
Schizont rupture and
Release merozoites that infect erythrocytes to become immature trophozoites of which…
Some mature and generate schizonts that rupture (feed back to 5)
Whilst some generate gametocytes that are ingested by mosquitos
To 12. are stages of reproduction in mosquito
Malaria Prophylaxis & Treatment uk
pregnancy
Prophylaxis
Depends on area visiting (risk) but commonly:
Doxycycline (POM)
proguanil + atovaquone (Malarone) – (P – Maloff Protect/POM - Malarone)
Mefloquine (POM)
Pregnancy: If cannot avoid travel, possible options: proguanil, chloroquine, mefloquine
Treatment (for uncomplicated cases)
1st choice is chloroquine for non-falciparum (P. malariae, P. ovale, P. vivax)
Chloroquine resistance common in most P. falciparum strains.
First line preference is:
Artemether + lumefantrine (Riamet)
[or dihydroartemisinin (aka artenimol) + piperaquine], if not available then:
Quinine + Doxycycline (or clindamycin),
Proguanil + atovaquone (Malarone),
Pregnancy: Quinine + clindamycin
Severe/complicated falciparum: Artesunate IV (initially)
Amoebic Dysentery & Amoebiasis
what is it
transmission
causes
treatment
Disease of tropics
~50 million cases/year
100,000 deaths
Transmission: Faecal-oral
Cause: Entamoeba histolytica
Commonly asymptomatic
Mild diarrhoea to severe dysentery
Extra-intestinal infections include liver abscesses
Digests (liquifies) human host cells (colon wall, neutrophils, liver cells)
Treatment:
Often self-limiting
Metronidazole (first line, acute invasive amoebic dysentery) or
Tinidazole followed by paromomycin/diloxanide furoate or other drugs active against cysts in the lumen
Toxoplasmosis
causes
symptoms
treatment
Cause: Toxoplasma gondii
Human exposure common (e.g. cat faeces or infected meat, unwashed fruit/vegetables)
Significant proportion adult population seropositive
Risk of developing disease low
Symptoms usually mild in healthy people
A few hundred reported cases in UK annually
Can be life threatening if immunocompromised
Also serious congenital infection:
Retinochoroiditis, seizures, and mental retardation.
Treatment: Often self-limiting
Most often pyrimethamine plus sulphadiazine (see malaria for mechanisms)
Alternative plus clindamycin, clarithromycin or azithromycin
Toxoplasmosis
causes
symptoms
treatment
Cause: Toxoplasma gondii
Human exposure common (e.g. cat faeces or infected meat, unwashed fruit/vegetables)
Significant proportion adult population seropositive
Risk of developing disease low
Symptoms usually mild in healthy people
A few hundred reported cases in UK annually
Can be life threatening if immunocompromised
Also serious congenital infection:
Retinochoroiditis, seizures, and mental retardation.
Treatment: Often self-limiting
Most often pyrimethamine plus sulphadiazine (see malaria for mechanisms)
Alternative plus clindamycin, clarithromycin or azithromycin
Cryptosporidiosis
causes
transmission
symptoms
treatment
Cause: Cryptosporidium parvum
~30% of western population seropositive
A notifiable infection in UK, a few thousand cases per year reported
Transmission:
Typically spread from water (swimming lakes / pools)
Contaminated foods / surfaces, common after flooding (also in UK)
No insect vector
Completes life cycle in human host, cysts passed out in faeces into water
Symptoms: Most common symptom watery diarrhoea, others include:
Dehydration, weight loss, stomach cramps or pain, fever, nausea, vomiting
Some people asymptomatic
Usually 1-2 weeks, cyclical - feel better, then worse again
Treatment:
Self-limiting but dangerous immunocompromised e.g. HIV/children/pregnancy
Usually don’t treat “normal” patients. Nitazoxanide (US, immunocompetent)
Helminths
parasitic worms
how does it reproduce
transmission
where does species attach to
what do they feed off
immune response
Most species attach to intestinal tract
Digestive enzymes dissolve worm egg shell, release the worm
Worm protected from digestive enzymes by external keratin layer
Helminths feed off host
take nourishment / protection
disrupts hosts’ nutrient absorption,
causes weakness / disease
Can be asymptomatic for months/yrs
Immune response to worm infection in humans is via T-helper cells
results in inflammation of the gut
results in cyst-like structures forming around the egg deposits throughout the body
Cestodes
causes
symptom
treatment
Cause: 2 subclases Cestoda
Cestodaria
Less common, unusual
Eucestoda - Most common, widespread
Taenia solium (pork tapeworm)
T. saginata (beef tapeworm)
Diphyllobothrium latum (fish tapeworm)
Head (“scolex”) which attaches to host
Neck, which differentiates into segments
Proglottids are body segments
Each male / female sex reproductive structures which can leave the host (faeces) and infect others
symptoms
Vary depending on infecting species, often:
upper abdominal discomfort
diarrhoea
loss of appetite
often asymptomatic
If untreated can cause intestinal blockages
Treatment:
Use Taenicides: niclosamide or praziquantel, unlicensed - Named patient basis
Nematodes: Pin/Threadworm
causes
diagnosis
treatment
Cause:
Enterobius vermicularis
Live ~6 weeks, lay eggs on perianal skin (up to 20,000/night)
Also secretes substances with eggs causes itching
Scratch, transmit under nails etc
Continued infection if eggs swallowed, worm released by digestive juices
Don’t enter blood, seldom serious except sleep-disturbance from itchiness/ crawling sensation
Diagnosis: Seeing worms in perianal region or “scotch tape test”
Sellotape around anus in morning, stick worms/eggs, look by microscope
Pinworms up to 13mm long, one side convex, other flat, colourless shell
Treatment: Mebendazole and good hygiene
