Microbiology
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Pathogens
A student who has recently returned from volunteering in sub-Saharan Africa presents to ED complaining that she has seen a worm in her stool. Diagnosis of roundworm is made by direct visualisation of characteristic eggs in stool on microscopy. What is the mode of transmission for roundworm:
Answer:
Ascaris lumbricoide eggs are ingested in contaminated food, water or soil. After hatching in the small intestine, the larvae penetrate the gut mucosa to reach the bloodstream and undergo a migratory cycle through the liver and lungs, where they are coughed up and swallowed, developing into the adult worm in the intestine and producing eggs that are released in faeces. N.B. Tapeworms are transmitted by people eating raw or undercooked beef or pork. Hookworm are transmitted by people walking barefoot or when exposed skin comes in contact with larvae in contaminated soil or sand. Fluke worms are transmitted by people swimming or washing in fresh water that contains fluke worms.Roundworm
Microbiology / Pathogens / Worms
Last Updated: 21st April 2019
Infection by roundworms e.g. Ascaris lumbricoides is prevalent in developing countries.
Life Cycle
Ascaris lumbricoide eggs are ingested in contaminated food, water or soil. After hatching in the small intestine, the larvae penetrate the gut mucosa to reach the bloodstream and undergo a migratory cycle through the liver and lungs, where they are coughed up and swallowed, developing into the adult worm in the intestine and producing eggs that are released in faeces.
Clinical Features
The severity of the symptoms is proportional to the number of worms present. A few worms may be asymptomatic but a greater parasite load may lead to vomiting and abdominal discomfort. Complications include pneumonitis, intestinal obstruction, malnutrition and hepatic abscess.
Diagnosis
Diagnosis is by direct visualisation of characteristic eggs in stool on microscopy.
Treatment
Mebendazole is effective against Ascaris lumbricoides and is generally considered to be the drug of choice.
Levamisole [unlicensed] (available from ‘special-order’ manufacturers or specialist importing companies) is an alternative when mebendazole cannot be used. It is very well tolerated.
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- Biochemistry
- Blood Gases
- Haematology
| Biochemistry | Normal Value |
|---|---|
| Sodium | 135 – 145 mmol/l |
| Potassium | 3.0 – 4.5 mmol/l |
| Urea | 2.5 – 7.5 mmol/l |
| Glucose | 3.5 – 5.0 mmol/l |
| Creatinine | 35 – 135 μmol/l |
| Alanine Aminotransferase (ALT) | 5 – 35 U/l |
| Gamma-glutamyl Transferase (GGT) | < 65 U/l |
| Alkaline Phosphatase (ALP) | 30 – 135 U/l |
| Aspartate Aminotransferase (AST) | < 40 U/l |
| Total Protein | 60 – 80 g/l |
| Albumin | 35 – 50 g/l |
| Globulin | 2.4 – 3.5 g/dl |
| Amylase | < 70 U/l |
| Total Bilirubin | 3 – 17 μmol/l |
| Calcium | 2.1 – 2.5 mmol/l |
| Chloride | 95 – 105 mmol/l |
| Phosphate | 0.8 – 1.4 mmol/l |
| Haematology | Normal Value |
|---|---|
| Haemoglobin | 11.5 – 16.6 g/dl |
| White Blood Cells | 4.0 – 11.0 x 109/l |
| Platelets | 150 – 450 x 109/l |
| MCV | 80 – 96 fl |
| MCHC | 32 – 36 g/dl |
| Neutrophils | 2.0 – 7.5 x 109/l |
| Lymphocytes | 1.5 – 4.0 x 109/l |
| Monocytes | 0.3 – 1.0 x 109/l |
| Eosinophils | 0.1 – 0.5 x 109/l |
| Basophils | < 0.2 x 109/l |
| Reticulocytes | < 2% |
| Haematocrit | 0.35 – 0.49 |
| Red Cell Distribution Width | 11 – 15% |
| Blood Gases | Normal Value |
|---|---|
| pH | 7.35 – 7.45 |
| pO2 | 11 – 14 kPa |
| pCO2 | 4.5 – 6.0 kPa |
| Base Excess | -2 – +2 mmol/l |
| Bicarbonate | 24 – 30 mmol/l |
| Lactate | < 2 mmol/l |
