PARASITOLOGY

• Malaria


  None motile protozoal disease

  
• Anopheles mosquitoes


  Transmit malaria

  
• Plasmodium species causing human infection

  • P.falciparum
  • P.vivax
  • P.malariae
  • P.ovale
  • P. knowlesi

  
• P.falciparum


  • Most important, rapid, most deadly
• P.falciparum accounts for >85% of malaria in East Africa

  
• 500 M people exposed to endemic malaria

  
• 1. 3 M deaths/yr (1-1.5 M children, mostly in Africa)
• Endemic malaria


  Areas of high transmission

  
• Epidemic malaria

  'Highland' & arid/semi-arid regions

  
• Imported malaria


  Travel & migration, any country

  
• Airport malaria


  Infected mosquitoes entering non-endemic areas, biting people living around airports

  
• Malaria life cycle

  1. Mosquito deposits sporozoites

  2. Sporozoites > liver schizonts > blood > RBCs trophozoites > schizonts (merozoites)

  3. Gametocytes > picked by mosquitoes > gametes > sexual reproduction > zygote > ookinete > oocysts > sporozoites > salivary glands

  
• Pre-erythrocytic interval


  • P. falciparum 6 days; P. vivax 8 days; P. ovale 9 days; P. malariae 13-16 days
• Merozoite invasion of RBCs

  • P. vivax infects young RBCs; P. malariae infects old RBCs; P. falciparum infects all RBCs
• Hypnozoite stage


  Sleeping/resting stage in P. ovale & P. vivax, responsible for relapsing malaria
• RBCs infected with P. falciparum stick together & stick to endothelium of blood vessels blocking capillaries of essential organs
• Simple uncomplicated malaria symptoms

  • Irregular fever, chills, headache, nausea, loss of appetite, dizziness, vomiting, muscle aches, joint pains, general malaise, diarrhoea, high temperature, jaundice, pallor, abdominal tenderness, splenomegaly, hepatomegaly

  
• Severe & complicated malaria symptoms

  • Cerebral malaria, convulsions, hypoglycaemia, hyperpyrexia, severe anaemia, renal failure, acidosis, hyperbilirubinaemia, pulmonary oedema/acute respiratory distress syndrome, haemoglobinuria, algid malaria, disseminated intravascular coagulopathy, abortion, premature birth, low birth weight, intrauterine death, hyper-reactive malaria splenomegaly

  
• Cerebral malaria


  Numerous petechiae appear in the brain
• Laboratory diagnosis - gold standard

  Thick + thin blood films, stained and examined under microscope

  
• Other diagnostic methods

  Antigen detection, QBC, PCR
• P. Falciparum microscopic features

  • RBCs not enlarged, rings appear fine & delicate, may have several in one cell, may have two chromatin dots, presence of marginal forms, Maurer's dots may be present
• Treatment of uncomplicated P. falciparum malaria

  1. Artemesinin combination treatment (ACT)

  2. Artemesinine + proguanil

  3. Artemesinine + sulphur/pyrimethamine

  4. Artemesinine + mefloquine

  5. Amodiaquine-artesunate

  6. Dihydroartemisinin-Piperaquine

  7. Pyronaridine-Artesunate

  8. Artemesinin+lumefantrine (Kenya)
• Treatment of severe/complicated P. falciparum malaria

  1. Quinine - IV

  2. + doxycycline

  3. Artesunate IM

  4. Treat other existing conditions (hypoglycaemia, anaemia, convulsions, renal failure, hyperpyrexia, pulmonary oedema)

  
• Treatment of P. ovale and P. vivax malaria

  1. Chloroquine

  2. Quinine

  3. ACTs

  4. Add Primaquine - kills hypnozoites
• Malaria prevention methods

  • Residual insecticide spray
  • Insecticide treated bed nets
  • Mosquito repellent
  • Mosquito larvicides
  • Mosquito window screens
  • Environmental management (clearing bushes, filling trenches, removal of old tyres, empty tins etc)
  • Protective clothing
  • Air-conditioners/fan

  
• Malaria prophylaxis

  • Mefloquine weekly
  • Doxycycline daily
  • Malarone (atovaquone+pyrimethamine)

  
• IPTp - Intermittent preventive treatment in pregnancy


  Sulphadoxine-pyrimethamine (SP) concentrates in placenta killing malaria parasites, reduces malaria attacks in mother, associated with better pregnancy outcomes
• Hookworm


  Intestinal nematode, found in small intestines
• Hookworm

  • Caused by Ancylostoma duodenalis & Necator americanus
  • Worldwide distribution, more in tropics
  • In Africa, Necator americanus predominates
  • Common in areas with poor sanitation
  • Disease called ancylostomiasis or necatoriasis
  • 2nd most common intestinal parasite, Ascaris lumbricoides (1st)
• Hookworm forms


  • Adults
  • Larvae
  • Eggs

  
• Adult hookworms

  • 1-1.5 cm in length
  • Females > males
  • A. duodenale has 2 pairs of teeth
  • N. americanus has cutting plates

  
• Hookworm eggs

  • Have a visible segmented ovum
• Hookworm larvae

  • Rhabditiform larvae - short and stout
  • Filariform larvae - infective form, long and slender

  
• Hookworm life cycle

  1. Adults in small intestine, mate, female lays eggs, eggs passed in stool

  2. Develop to release rhabditiform larvae (7 days), then to filariform stage (7 days)

  3. Penetrate skin of man (usually feet), get into blood circulation, go to heart, lungs, out of blood, bronchi, coughed out, ascend trachea to epiglottis, swallowed

  4. Stomach > small intestine attach to mucosa, develop to adult

  5. From skin penetration to adult: 6-8 weeks

  6. A. duodenale also infect via mucous membrane in mouth
• Hookworm infection

  • Early infection - dermatitis (ground itch), dry cough, dyspnoea, abdominal pain & discomfort
  • Light infection often asymptomatic
  • Heavy infection - anaemia: pallor, leg swelling, dyspnoea, palpitation, PBF- hypochromic microcytic; anaemia = sucking of blood (A.duodenale > N.americanus), bleeding sites, anticoagulants from worms
  • Black stool (melena). digested blood from upper GIT bleed
• Hookworm diagnosis

  1. Stool microscopy - characteristic eggs

  2. Stool (non-fresh) - rhabditiform larvae

  3. Kato-Katz technique - Parasite quantification

  
• Hookworm treatments

  • Albendazole
  • Mebendazole
  • Levamisole
  • Bephenium hydroxynaphthoate
  • Pyrantel pamoate
• Supportive hookworm treatment

  • Iron supplements
  • Transfusion of blood if anaemia is severe
• Hookworm prevention and control

  • Proper faecal disposal - pit latrines etc
  • Don't use untreated human waste as manure
  • Wearing of protective shoes
  • Health education on how infection is transmitted and how it can be prevented
  • Treatment of infected persons
  • Treatment of soil