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Microbiology > Tropical Diseases > Flashcards

Tropical Diseases Flashcards

1
Q

Protozoa

A
  • Protozoa can be subdivided into:
    • Sporozoa (all intracellular) eg Malaria parasites
    • Flagellates eg Trypanosomiasis, Trichomonas, Giardia
    • Amoebae eg Entamoeba histolytica
    • Ciliates (don’t cause disease in man)
  • Transmission may be by:
    • Ingestion eg E.histolytica, Giardia, Cryptosporidium
    • Inhalation eg Pneumocystis carinii
    • Inoculation – Using an insect vector eg malaria, Trypanosomiasis, Leishmaniasis
    • Sexually eg Trichomonas
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2
Q

Malaria

A
  • Caused by the malaria parasite – a protozoan (plamodium genus)
  • 4 types of human malaria:
    • Plasmodium vivax
    • Plasmodium falciparum
    • Plasmodium ovale
    • Plasmodium malariae
  • Humans are the reservoir for human malaria.
  • Transmission is by the bite of female anopholese mosquitoes
  • Other forms of transmission have been documented rarely. These include: blood transfusion, lab accidents, needlestick injuries, congenital transmission, imported mosquitoes at international airports
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3
Q

Malaria - Epidemiology

A
  • Endemic in the Tropics and sub-tropics eg S.America, SE Asia, sub-Saharan Africa but note slightly different distributions for different types of malaria
  • Affects anyone, but symptomatology may vary depending on certain host genetic factors, or partial immunity in people who have been living in the area for many years
  • 300-500 million people infected with malaria per year
  • 1 million deaths from malaria per year – mainly affects children <5years of age
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4
Q

Malaria - Life Cycle

A
  • Female *anopheles *mosquito inject motile infective sporozoite form of plasmodium into human (or animal) bloodstream
    • Travels to and infects hepatocytes in the liver - asexual reproduction until cell bursts releasing thousands of meozoites
      • Travel through blood infecting RBCs - reproducing asexually till cell ruptures and repeating the cycle
      • Some merozoites develop into immature gametocytes (male and female precursors) - taken up by another mosquito biting the human
        • Fuse into ookinete (a fertilized zygote) in mosquito guy ==> travel to mosquito salivary glands to infect another host
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5
Q

Malaria - Incubation Period

A
  • Onset classically 7-30 days after mosquito bite depending on the species (pre-patent period)
  • In P.vivax malaria incubation may rarely take up to 1 year
  • P.vivax and P.ovale can also exist as dormant forms (hypnozoites) that produce relapses months or years later
  • Consider malaria in anyone with a fever who has been in an at-risk area within the last year
  • Note also that viral haemorrhagic fevers should be considered in anyone who has been to an area where this is endemic within the 3 weeks prior to the onset of their symptoms especially if:
    • Contact with somone who was unwell
    • Contact with rodents
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6
Q

Malaria - Clinical Features

A
  • Flu-like symptoms:
    • Fever, rigors, sweats, malaise, myalgia
  • Respiratory Symptoms
    • Cough, respiratory distress, pulmonary oedema
  • GI symptoms
    • Nausea, vomiting, diarrhoea, jaundice, liver failure
  • CNS symptoms
    • Headaches, confusion, coma – cerebral malaria
  • Shock
  • Acidosis
  • Renal impairment
  • “Blackwater fever”
  • Anaemia, DIC
  • Hypoglycaemia
  • Splenic rupture
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7
Q

Viral Haemmorrhagic Fevers

A
  • Consider as a differential for fever in those with any of the risk factors:
    • Travel to high risk area in the last 21 days
    • Contact with human or animal with suspected VHF (body fluids/tissues)
    • Ingestion of bush meat
      • Restrict investigations to malaria film only intitally to rule out as differential - VHF very infectious and requires patient isolation and special blood handling proceedures
  • Types:
    • Lassa
    • Ebola
    • Marburg
    • CCHF
  • Common clinical fatures = VHF syndrome:
    • Capillary leak
    • Bleeding diathesis (susceptibility to bleeding/haemmorhage)
    • Circulatory compromise ==> shock
      • Plus fever
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8
Q

Malaria - Investigations

A
  • If you suspect VHF as a differential - do a malaria film only
  • Thick and thin malaria film at 12-24 hour intervals
    • Assume P.falciparum (most severe form) until films have had specialist review
  • Malaria antigen test
  • FBC – decreased platelets, anaemia
  • Clotting screen
  • U&Es, LFTs
  • Blood cultures - baterial coinfection in approximately 15% of patients
  • Serology – eg dengue fever
  • ABG - pH
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9
Q

Malaria - Management

A
  • Antimalarials:
    • P.falciparum regimen = quinine followed by fansidar or doxycycline
    • Benign malarias = chloroquine (check local resistance patterns first) followed by primaquine for cases of P.vivax or P.ovale
      • ​Check for G6PD deficiency before giving primaquine
    • ​Newer antimalarials:
      • ​Artemether
      • Mefloquine
      • Malarone
  • Supportive therapy – correct shock , anaemia, bleeding abnormality, treat or prevent convulsions, hypoglycaemia, intercurrent infections
  • Avoid overhydration
  • in severe cases consider exchange transfusion and HDU
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10
Q

Malaria - Prevention

A
  • Protection against bites:
    • Bed nets
    • Insect repellants
    • Clothing to avoid bites at dusk & dawn
    • Screens on doors and windows
  • Protection against infection:
    • Prophylaxis
    • Future role of immunisation
  • Prevent parasite life cycle:
    • Prompt effective treatment in endemic areas
    • Local measure eg. pesticides, avoid pooling of water
    • Potential role for Altruistic vaccine
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11
Q

Protozoal Infections - Leishmaniasis

A
  • Several types of leishmaniasis broadly categorised into:
  • Visceral leishmaniasis (kala azar) – characterised by hepatosplenomegaly
    • ​Seen in S.America, Africa, India and the Mediterranean
  • Cutaneous leishmaniasis – tropical sore
    • ​Seen in Aftrica, India, S. America and the Mediterranean
  • Transmission: Sandflies
  • Dx: Biopsy
  • Rx Antimonials, pentamidine, amphotericin
  • Prevention: impregnated bed nets, elimination of animal vector eg dog control
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12
Q

Protozoal Infections - Tyrpanosomiasis - Sleeping Sickness

A
  • Trypanosomiasis
    • Sleeping sickness – Africa
      • ​Tsetse fly transmits from wild animals to man
      • Diagnsosis:
        • Visualisation of parasites on lymph node biopsy or in the CSF
        • Raised serum IgM is characteristic
      • ​Rx
        • Arsenicals eg melarsan
        • Non-arsenicals eg suramin, pentamidine
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13
Q

Protozoal Infections - Typanosomiasis - Chagas Disease

A
  • ​Chagas disease – S.America
    • Rejuvid blood transmits to man causing:
      • ​

Megaoesophagus

    * Megacolon
    * Cardiomyopathy
* ​Diagnosis:
    * Visualisation of parasites in blood
    * Serology
    * Xenodiagnosis
* ​Rx - Arsenicals
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14
Q

Helminths

A
  • 3 main groups:
    • Nematodes - round worms
    • Trematodes - flukes
    • Cestodes - tapeworms
  • Transmission through
    • Ingestion:
      • Of eggs/larvae from the faeces of an infected host eg. threadworm
      • Of soil or food contaminated by soil in which larvae have developed from eggs passed in the faeaces of an infected host eg. ascaris lubricoides
      • Ingestion of larvae in the tissue of an intermediate host eg. Taenia species
    • ​Inoculation
      • By a blood sucking insect eg. filariasis
      • By active penetration of the larvae eg. schistosomiasis, hookworms
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15
Q

Helminth Infections - Schistosomiasis (Bilharzia)

A
  • A trematode that infects man
    • Through contact with water containing the parasite - released by infected freshwater snails
  • 3 species affect humans:
    • S.haematobium – affects urine. Prevalent in Africa, parts of Arabia, Near East, Madagascar, Mauritius
    • S. mansonii – affects bowel. Found in Africa and Madagascar. Some exported during the slave trade to Carribean and S. America
    • S.Japonicum – affects bowel. Found in Japan, China, Philippines, Sulawesi
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16
Q

Helminth Infections - Schistosomiasis (Bilharzia) - Symptoms

A
  • May be none - **! **history of exposure
  • “Swimmer’s itch”
  • “Katayama fever” – a seroconversion illness characterised by fever, arthralgia, urticarial rash
  • Bloody diarrhoea
  • Abdominal pain
  • Haematuria
  • Portal hypertension ==> oesophageal varices and haematemesis
  • Malignancy - bladder cancer
  • Paraparesis
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17
Q

Helminth Infections - Schistosomiasis (Bilharzia) - Investigations and Treatment

A
  • Investigations:
    • Ova in urine, stool or biopsy sample
    • Immunodiagnosis
    • Eosinophilia
  • Rx - Praziquantel
18
Q

Helminth Infections - Ascaris Lumbricoides

A
  • Soil-transmitted
  • 15-40cm cream coloured worms that live in the small intestine.
  • Eggs passed in the stool and develop into the infective stage in soil where they may remain infective for several months.
    • Ingested eggs hatch in the intestine and the larvae migrate to the lungs via the circulation.
      • After a period of maturation, larvae migrate up the ciliary escalator to the epiglottis where they are swallowed and reach their final habitat.
19
Q

Helminth Infections - Ascaris Lumbricoides - Symptoms

A
  • Symptoms – frequently infection is asymptomatic.
  • However patients may have a number of symptoms which include:
    • Mechanical, toxic and metabolic effects of worms in intestine
    • Loeffler’s syndrome as worms pass through the lungs:
      • Wheezing
      • Cough
      • Fever
      • Dyspnoea
      • Moving X-ray shadows
      • Eosinophilia
20
Q

Helminth Infections - Ascaris Lumbricoides - Investigation and Treatment

A
  • Dx: By seeing typical eggs in the stools or the passing of a worm
  • Rx:
    • Piperazine salts
    • Pyrantel
    • Mebendazole
21
Q

Helminth Infections - Strongyloides Stercoralis

A
  • Soil-transmitted
  • A 2mm worm inhabiting the small intestinal mucosa of man.
  • Life cycle: Eggs or larvae released in the stool develop in the soil. Females will lay further larvae which are infective in the right environmental conditions.
    • These penetrate the intact skin of passers by.
      • They migrate to the small intestine via the lung.
    • Some larvae can reach the infective stage without having to go through a soil stage and result in autologous infection allowing infection to last 40 years.
22
Q

Helminth Infections - Strongyloides Stercoralis - Symptoms

A
  • Early infections may cause symptoms similar to ascaris and hookworm:
    • Itchy papule at site of penetration
    • Respiratory symptoms during lung stage
    • Upper abdo pain and diarrhoea including steatorrhoea
    • Weight loss
    • Eosinophilia
    • Chronic infection is rarely of clinical importance except in immunosuppressed individuals where the worm load may become massive.
      • Rarely people get in an itchy skin rash during migration (larva currens) and vague abdominal symptoms with occasional loose stool.
        • Immunosupressed individuals may also get:
          • More severe diarrhoea
          • Paralytic ileus
          • Gram negative sepsis (when the larvae take bacteria with them as they pass through the bowel wall)
          • Pulmonary syndrome
          • Specific organ involvement including encephalitis
23
Q

Helminth Infections - Strongyloides Stercoralis - Investigation and Treatment

A
  • Dx:
    • Stool microscopy for larvae direct or concentration method
    • Microscopy of duodenal aspirate, string test or jejunal biopsy for larvae or sometimes eggs and adult worms
    • Stool culture for larvae/worms
    • Serology eg ELISA for strongyloides antigen
    • Eosinophilia
  • Rx:
    • Thiabendazole
    • Albendazole
24
Q

Helminth Infections - Hookworm (Ancylostoma duodenale and Necator Americanus)

A
  • Small (1cm) blood sucking worms inhabiting the small intestine
    • ​Mature into larvae in soil and penetrate intact skin of passersbywhere
      • From there to gut then like ascaris the larvae pass via the lungs up the ciliary escalator to the epiglottis where they are swallowed and reach the duodenum.
25
Q

Helminth Infections - Hookworm (Ancylostoma duodenale and Necator Americanus) - Symptoms

A
  • Itchy papule at site of penetration
  • Occasional mild lung symptoms
  • Iron deficiency anaemia and its symptoms
  • Protein loss resulting in hypoalbuminaemia and its symptoms
26
Q

Helminth Infections - Hookworm (Ancylostoma duodenale and Necator Americanus) - Investigation and Treatment

A
  • Dx:
    • Eggs in stool (hatched larvae in stool if delayed viewing at high temps)
    • Iron deficiency anaemia
    • Eosinophilia
  • Rx:
    • Iron replacement
    • Worm eradication with Pyrantel, Mebendazole or other drugs
    • Health education (latrines, footwear etc)
27
Q

Helminth Infections - Whipworm (Trichuris trichuria)

A
  • Soil-transmitted
  • 2-5cm long with narrow anterior end embedded in mucosa of large bowel
    • Feeds on juices rather than blood
    • Eggs passed in faeces embryonate in soil
      • If swallowed hatch and go directly to the large bowel without a migratory phase
28
Q

Helminth Infections - Whipworm (Trichuris trichuria) - Symptoms

A
  • Usually none, but if heavily infected can get:
    • Bloody diarrhoea
    • Rectal prolapse
    • Anaemia
    • Eosinophilia
    • Weight loss
29
Q

Helminth Infections - Whipworm (Trichuris trichuria)

A
  • Dx:
    • Eggs in stool
  • Rx:
    • Mebendazole for heavy infections
    • Albendazole for adults
30
Q

Helminth Infections - Toxocara Catis and Cani

A
  • The only nematode not transmitted via the soil
  • These are tapeworms of dogs and cats that accidentally infect man when eggs are ingested from soil or dogs’ fur
    • ==> Causes visceral larva migrans (VLM) as the larvae migrate through the tissues for up to 1-2 years
      • ​Symptoms of generlised VLM:
        • ​Fever
        • Eosinophilia
        • Hepatomegaly
        • Asthma
    • Both flukes and tapeworms eggs develop into larvae that have to pass through an intermediate host and develop into other larval stages before they are infective to man again
31
Q

Helminth Infections - Enterobius Vermicularis (Threadworm)

A
  • Common intestinal parasite in humans - condition = enterobiasis
  • Most common helminth infection in the western world
    • Particularly common in children - estimated prevalence of 50% in UK
    • Human to human transmission from ingesting eggs (faeco-oral) - remain viable for up to 3 weeks
  • Entire life cycle takes place in human GI tract:
    • Ingested eggs hatch in duodenum
    • Larvae migrate through small intestine to colon maturing to adults
      • Males and females mate in the ileum
        • Males dies and are passed out
        • Females attatch in caecum, ileum, appendix and ascending colon and ingest colonic contents as they fill with eggs
          • Migrate through colon and out anus ==> primary symptom of enterobiasis: anal itching
            • Deposit eggs through:
              • Contraction and expulsion
              • Dying and disintergrating
              • Bodily rupture from host scratching
  • Rx:
    • Albendazole or Mebendazole is the first-line tratment
    • Pyrantel Pamoate is alternative
32
Q

Helminth Infections - Tapeworms - Taenia Saginata (Beef Tapeworm)

A
  • Larval cysts in “measly meat” are ingested and hatch into worms on arrival in the intestine
    • The head of the worm embeds itself into the wall of the small intestine by suckers and new proglottid segments grow at the tail end ==> between 1000-2000 segments (up to 5metres!)
      • Proglottids at the tail end develop fertilised eggs which are released either within a broken off proglottid or as free eggs in the stool
        • Eggs released into pasture reinfect cattle where they develop into larvae in the muscle.
33
Q

Helminth Infections - Tapeworms - Taenia Saginata (Beef Tapeworm) - Symptoms

A
  • Patients may be asymptomatic
  • Motile proglottids emerging from the anus can cause some distress
  • Patients may have vague abdominal pains
34
Q

Helminth Infections - Tapeworms - Taenia Saginata (Beef Tapeworm) - Investigation and Treatment

A
  • Dx:
    • Finding of eggs in the stool
    • Examination of proglottid – distinguished from T. solium by ovarian branching pattern
  • Rx:
    • Praziquantel
    • Niclosamide
35
Q

Helminth Infections - Taenia Solium (Pork Tapeworm)

A
  • As for T. solium except that the larval form is found in pork rather than beef
  • Unlike T.saginata, the ova of T. solium can infect humans so that the cystic form is also found in man
    • Usually causes asymptomatic cysts within the muscle - may ==> serious symptoms if the cysts end up elsewhere eg. the brain
      • Diagnosis of this form of the disease, known as cystercicosis, is usually circumstantial with evidence of spindle shaped calcified lesions in the muscles (particularly the thighs) or by CT scan.
  • Serology may also be positive but there is cross reactivity with other helminths.
  • Rx:
    • Albendazole
    • Praziquantel
36
Q

Helminth Infections - Hydatid Disease (Ecchinococcus)

A
  • This is a tapeworm of dogs that usually has the cystic stage of its life cycle in sheep, cattle and other ungulates.
    • Man is an accidental host, infected by ingesting the tapeworm eggs
      • The cysts can grow anywhere though are commonly found in the liver, spleen and lungs where they can grow to an enormous size
        • Rarely, they go to the brain, the heart or elsewhere and cause local symptoms
      • Cysts may contain daughter cysts
        • Can lead to anaphylaxis or seeding of cysts within the host
37
Q

Helminth Infections - Hydatid Disease (Ecchinococcus) - Investigation and Management

A
  • Dx:
    • ​

USS/X ray/CT imaging

* Serology * ​

Rx:

* ​ * Albendazole*

* Surgical removal of intact cysts (NB anaphylaxis likely if cyst ruptures)
38
Q

Helminth Infections - Filariasis - Symptoms

A
  • Patients may be asymptomatic​
  • Can develop recurrent lymphangitis
    • If recurrent may ==> elephantiasis due to irreversible damage to the lymphatic system
39
Q

Helminth Infections - Filariasis

A
  • Caused by Wucheria bancrofti and Brugia malayi
    • ​Found in Africa, Asia, S.America and Oceania
    • Worms are transmitted by mosquitoes and live in the lymphatics mainly of the groins and axillae
      • Microfilariae are released into the blood by female worms and may be taken up by a mosquito where they develop into infective larvae.

Dx: Blood samples taken around midnight may demonstrate microfilariae

Serology

Rx: Diethylcarbamazine or Ivermectin

There is no effective treatment for chronic elephantiasis other than major surgery

40
Q

Helminth Infections - Filariasis - Investigation and Treatment

A
  • Dx:
    • Blood samples taken around midnight may demonstrate microfilariae
    • Serology
  • ​Rx:
    • Diethylcarbamazine or Ivermectin
    • There is no effective treatment for chronic elephantiasis other than major surgery

Microbiology (10 decks)

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