Tropical Diseases

Question 1

Protozoa

Answer 1

• 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

Question 2

Malaria

Answer 2

• 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

Question 3

Malaria - Epidemiology

Answer 3

• 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

Question 4

Malaria - Life Cycle

Answer 4

• 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

Question 5

Malaria - Incubation Period

Answer 5

• 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

Question 6

Malaria - Clinical Features

Answer 6

• 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

Question 7

Viral Haemmorrhagic Fevers

Answer 7

• 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

Question 8

Malaria - Investigations

Answer 8

• 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

Question 9

Malaria - Management

Answer 9

• 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

Question 10

Malaria - Prevention

Answer 10

• 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

Question 11

Protozoal Infections - Leishmaniasis

Answer 11

• 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

Question 12

Protozoal Infections - Tyrpanosomiasis - Sleeping Sickness

Answer 12

• 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

Question 13

Protozoal Infections - Typanosomiasis - Chagas Disease

Answer 13

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

Megaoesophagus

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

Question 14

Helminths

Answer 14

• 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

Question 15

Helminth Infections - Schistosomiasis (Bilharzia)

Answer 15

• 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

Question 16

Helminth Infections - Schistosomiasis (Bilharzia) - Symptoms

Answer 16

• 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

Question 17

Helminth Infections - Schistosomiasis (Bilharzia) - Investigations and Treatment

Answer 17

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

Question 18

Helminth Infections - Ascaris Lumbricoides

Answer 18

• 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.

Question 19

Helminth Infections - Ascaris Lumbricoides - Symptoms

Answer 19

• 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

Question 20

Helminth Infections - Ascaris Lumbricoides - Investigation and Treatment

Answer 20

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

Question 21

Helminth Infections - Strongyloides Stercoralis

Answer 21

• 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.

Question 22

Helminth Infections - Strongyloides Stercoralis - Symptoms

Answer 22

• 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

Question 23

Helminth Infections - Strongyloides Stercoralis - Investigation and Treatment

Answer 23

• 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

Question 24

Helminth Infections - Hookworm (Ancylostoma duodenale and Necator Americanus)

Answer 24

• 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.

Question 25

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

Answer 25

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

Question 26

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

Answer 26

* 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)

Question 27

Helminth Infections - Whipworm (Trichuris trichuria)

Answer 27

* 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

Question 28

Helminth Infections - Whipworm (Trichuris trichuria) - Symptoms

Answer 28

* Usually none, but if heavily infected can get: * Bloody diarrhoea * Rectal prolapse * Anaemia * Eosinophilia * Weight loss

Question 29

Helminth Infections - Whipworm (Trichuris trichuria)

Answer 29

* Dx: * Eggs in stool * Rx: * *Mebendazole* for heavy infections * *Albendazole* for adults

Question 30

Helminth Infections - Toxocara Catis and Cani

Answer 30

* 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

Question 31

Helminth Infections - Enterobius Vermicularis (Threadworm)

Answer 31

* 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

Question 32

Helminth Infections - Tapeworms - Taenia Saginata (Beef Tapeworm)

Answer 32

* 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.

Question 33

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

Answer 33

* Patients may be asymptomatic * Motile proglottids emerging from the anus can cause some distress * Patients may have vague abdominal pains

Question 34

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

Answer 34

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

Question 35

Helminth Infections - Taenia Solium (Pork Tapeworm)

Answer 35

* 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*

Question 36

Helminth Infections - Hydatid Disease (Ecchinococcus)

Answer 36

* 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

Question 37

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

Answer 37

* Dx: * ​ USS/X ray/CT imaging * Serology * ​ Rx: * ​ * Albendazole* * Surgical removal of intact cysts (NB anaphylaxis likely if cyst ruptures)

Question 38

Helminth Infections - Filariasis - Symptoms

Answer 38

* Patients may be asymptomatic​ * Can develop recurrent lymphangitis * If recurrent may ==\> elephantiasis due to irreversible damage to the lymphatic system

Question 39

Helminth Infections - Filariasis

Answer 39

* 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

Question 40

Helminth Infections - Filariasis - Investigation and Treatment

Answer 40

* 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