Parasitic Infections Flashcards
Define Infection
invasion by and growth of
pathogenic microorganisms
within the body
Define Disease
a disordered or incorrectly functioning organ, part, structure, or system of the body resulting from the effect of genetic or developmental errors, infection, poisons, nutritional deficiency or imbalance, toxicity, or unfavorable environmental factors; illness; sickness; ailment.
Define parasites
Parasite - organism living in or on the host and
dependent on it for nutrition - causing
damage
What is the differences between endoparasites and ectoparasites
Endoparasite – exist INSIDE the host
Ectoparasite – exist on the host (on the skin)
Give some examples of endoparasites
Protozoa: amoeba, coccidiae, ciliate, flagellates
Metazoa: roundworms, flatworms, flukes
What are protozoa
Protozoa – single celled organisms
Eukaryotes (genome within a nucleus, complex organelles in cytoplasm)
Pathogenesis (mechanism of disease) varied
Some have insect vectors (eg malaria)
No eosinophilia
What are metazoan
Metazoa – Multicellular organisms (Helminths/worms)
Free living, intermediate hosts and vectors
Some just inhabit gut (geohelminths), other invade tissues
Eosinophilia – if invade blood
State two amoeba
Amoebae: Entamoeba histolytica, Entamoeba dispar Entamoeba hystolytica (pathogenic)/dispar (commensal)
Entamoeba hystolytica (pathogenic)/dispar (commensal)
Summarise the amoeba organisms
- Entamoeba histolytica
- Entamoeba dispar
Infection occurs by ingestion of mature cysts in food or water, or on hands contaminated by faces- good hygiene is paramount
Describe the epidemiology of amoeba infections
About 10 % of the world’s population is infected with E.histolytica
Third most common cause of death of parasitic infections (after schistomiasis and malaria)
common in South + Central America, West + South-East Asia; rare in temperate climates
~ 90% of infections are asymptomatic; the remaining 10% produce a spectrum of diseases varying from dysentery to amoebic liver abscess
Incubation period may be as short as 7 days; tissue invasion mostly occurs during first 4 months of infection
Outline the life cycle of E.histolytica
Contamination by mature cyst (four nuclei) - by food or water
Excystation- one trophoblastzoite with four nuclei emerges, divides three times and each nucleus divides once to produce 8 trophozoites from each cyst.
Trophozoites migrate to the large intestine and multiply by binary fission
Trophozoites invade the intestinal mucosa – invasive infection through the bloodstream infecting sites such as liver, brain, and lungs
After multiplying by binary fission- one will undergo encystation to form a immature cyst
which then forms a quadrinucleate cyst
cyst will exit in the stool - noninvasive infection
Incubation period may be as short as 7 days; tissue
Describe the key features of the life cycle of E.histolytica
Humans are the only reservoir, and infection occurs by
ingestion of mature cysts in food or water, or on hands
contaminated by faeces.
• The cysts of E. histolytica enter the small intestine and
release active amoebic parasites (trophozoites), which
invade the epithelial cells of the large intestines, causing
flask-shaped ulcers. Infection can then spread from the
intestines to other organs, e.g. liver, lungs and brain, via the
venous system.
• Asymptomatic carriers pass cysts in the feces and the
asymptomatic carriage state can persist indefinitely. Cysts
remain viable for up to 2 months.
Invasive amoebiasis most often causes an amoebic liver
abscess, but may affect the lung, heart, brain, urinary
tract and skin.
E. histolytica (the cause of invasive amoebiasis) must be
differentiated from Entamoeba dispar, which is a normal
commensal of the gastrointestinal tract.
Describe the laboratory diagnosis of amebiasis
E.histolytica and E.dispar are morphologically identical species. In bright-field microscopy, E.histolytica and E.dispar cysts are spherical and usually measure 12-15microns (range may be 10-20 microns). A mature cyst has 4 nuclei, but an immature cyst may only have 1-3 nuclei.
Describe the treatment for amebiasis
Nitroimidazole derivatives (act on trophozoite, but not on cysts) + parmomycine or diloxanide furoate
Summarise the coccidia
Coccidia
Coccidial infection in humans are mostly zoonoses
Plasmodium species - malaria
- Toxoplasma - toxoplasmosis
- Cryptosporidium- diarrhoea
Summarise the different diseases caused by coccidia
Malaria
Toxoplasmosis: mild disease in immunocompetent individuals:
fever, swollen lymph nodes, headaches, sore throat.
however, in pregnancy: toxoplasmosis poses serious danger for the
Foetus)
Diarrhoea (mild disease in immunocompetent individuals,
the parasites can cause serious pathological changes in
immunocompromised individuals)
Describe the different types of plasmodium species
Different types of plasmodium: P. falciparum, P. malariae, P. ovale, P. vivax and P. knowlesi
2 types of host: humans and female Anopheles mosquitoes (~ 20 different Anopheles species are locally important around the world. All of the important vector species bite at night. Anopheles mosquitoes breed in water)
2 stages in human: liver and blood stages
Falciparum more serious
Outline the life cycle for plasmodium
Mosquito takes a blood meal (injects sporozoites) infects liver cell –forming schizont and then a ruptured schizont
Infective- exo-erythrocytic cycle.
Then enters the blood
immature trophozoite (ring stage)
divides to form a mature trophozoite and a gametocyte
mature trophozoite forms a schizont which then ruptures - erythrocytic cycle
gaemtocytes divide by meiosis
mosquito takes a blood meal and ingests gametocytes
forming macro gametocytes with flagellated micro gametocytes
ookinete
oocyst which then ruptures to release sporozoites which will infect another host when the mosquito takes another blood meal.
Describe the epidemiology and symptoms of malaria
In 2013, there were ~198 million cases of malaria, causing an estimated 584 000 deaths, mostly among African children (one child dies every 30 seconds).
Symptoms:
Can appear as early as 7 days but the time between exposure and signs of illness can be as long as one year.
- 9 to 14 days for Plasmodium (P.) falciparum.
- 12 to 18 days for P. vivax and P. ovale.
- 18 to 40 days for P. malariae.
- 11 to 12 days for P. knowlesi.
Fever, headache, chills, vomiting, muscle pain
Paroxysm (cycle in 4-8hrs)
Describe the complications of malaria
Complications of malaria: Severe anemia (destruction of red cells) Cerebral malaria (swelling of the brain,seizures, coma)
liver failure Shock Pulmonary edema abnormally low blood sugar kidney failure swelling and rupturing of the spleen
Describe the treatment of malaria
Uncomplicated malaria:
chloroquine, Atovaquone-proguanil, Artemether-lumefantrine, quinine sulfate plus one of the following: Doxycycline, Tetracycline or Clindamycin Quinine sulfate, Mefloquine
Severe malaria:
Artemisinin-based combination therapy (ACT) is recommended for the treatment of P. falciparum malaria.
Resistance an issue for treatments
Describe the diagnosis of malaria
blood film, Giemsa stained
Rapid test: commercially available antigen detection tests: more expensive and less sensitive
Describe the transmission routes for toxoplasma gondii
Humans can become infected by any of several routes:
• eating undercooked meat of animals harboring tissue cysts
• consuming food or water contaminated with cat feces
• by contaminated environmental samples
• blood transfusion
• organ transplantation
• transplacentally from mother
to fetus.
Infect warm blooded animals
Which group of patients are particularly vulnerable to toxoplasma gondii
Immunocompromised patients may develop central nervous system disease, brain lesions, pneumonitis or retinochoroiditis among other risks.
How do we diagnose toxoplasma gondii
Serological tests are available
What does cryptosporidium cause
Causes diarrhea, fever, nausea, vomiting in humans; very common in HIV+ patients presenting with diarrhea.
cryptosporidiosis
Describe the diagnosis and treatment for cryptosporidiosis
Diagnosis: stool examination.
Treatment: fluid rehydration.
Water is the vector- contaminated oocysts
Summarise ciliates
Balantidium coli
(Balantidiasis)
Reservioir hosts:
Primates
Rodents
Pigs
Worldwide distribution
Summarise balantidiasis
Most people infected with Balantidium coli => no symptoms.
Immunocompromised patients may experience more severe signs and symptoms: persistent diarrhea, dysentery, abdominal pain, weight loss, nausea, and vomiting. If left untreated, perforation of the colon can occur.
Diagnosis: stool examination
Treatable
Summarise flagellates
Giardia lamblia
(Giardiasis)
Giardiasis: commonest, globally distributed, water-borne protozoal
infection.
Flagellated trophozooites attach by their suckers to surface of the
duodenal or jejunal mucosa
Ovoid cysts are able to survive standard chlorination procedures,
filtration is required to exclude them from drinking water
Diarrhoea
Two stages:
trophozoites
cysts
Describe the key features of giardiasis
Epidemiology
~2% of adults and 6% to 8% of children in developed countries worldwide; ~ 33% of people in developing countries
Symptoms Most people infected with Balantidium coli => no symptoms. Acute symptoms: Diarrhea Greasy stools that tend to float Stomach or abdominal cramps Upset stomach or nausea/vomiting Dehydration (loss of fluids)
Diagnosis
Stool examination:
Treatment: metronidazole/tinidazole
How is trichomonas ( a flagellate) transmitted
Transmitted sexually
What is important to remember about trichomoniasis
Trichomoniasis
It is estimated to be the most common, curable, non-viral sexually transmitted infection in the UK, with nearly 6000 new cases per year.
Describe the key features of trichomoniasis
In women the organism is found in the vagina, urethra and paraurethral glands; in men infection is usually of the urethra.
TransmissionIn adults transmission is almost exclusively through sexual intercourse.
Symptoms
Females10-50% are asymptomatic.=> vaginal discharge, vulval itching, dysuria, or offensive odour, but these are not specific for TV.Occasionally the presenting complaint is of low abdominal discomfort or vulval ulceration.
Males
15 to 50% of men are asymptomatic
=> discharge and/or dysuria.
ComplicationsDetrimental outcome on pregnancy and is associated with preterm delivery and low birth weight.
HIV
There is growing evidence that trichomonas infection may enhance HIV transmission and there may be an increased risk of TV infection in those that are HIV positive.
Diagnosis
Microscopy: Detection of motile trichomonads in swab/urine- Trichomonas Rapid Test
Treatment
metronidazole
What is another important flagellate
Flagellates: Leishmania
Summarise the key features of helminths (metazoan)
Complex o Multicellular parasites.
o Cycles may involve insect vectors and intermediate hosts.
For most, humans are the definitive host – a few are zoonoses (acquired from animals).
o Adult worms cannot multiply in man – the number of adults is related to the infection.
o A large burden is found in school-aged children which has a massive effect on their development- massive impact for future economy of the country
Lay eggs, microfilaria, larvae
What are the most common helminth infections worldwide
Ascariasis
Trichuriasis
Hookworm infection
Schistosomiasis
What are the 3 groups of helminths
Roundworms (nematodes) • Ascaria • Hookworms • Filaria • Strongyloides Flatworms (cestodes) • Taenia (tapeworms) Flukes (trematodes) • Schistosoma
Eosinophilia in invasive worms
