Microbiology
Pathogens
Regarding chickenpox, which of the following statements is CORRECT:
Answer:
Recovery from chickenpox usually provides lifelong immunity. Transmission is by direct contact or airborne spread from patients with vesicles, and it is very contagious to non-immune individuals. Infection is most common in children aged 4 - 10 years and usually results in only mild systemic features with a widespread itchy rash which usually resolves after about 7 - 10 days. Infection in neonates, adolescents/adults and pregnant women may result in more severe systemic disease.Varicella Zoster Virus (VZV)
Microbiology / Pathogens / Herpes Viruses
Last Updated: 1st June 2023
Varicella zoster virus (VZV) causes chickenpox and shingles.
Transmission
Transmission is by direct contact or airborne spread from patients with vesicles, and it is very contagious to non-immune individuals. The incubation period is about 10 - 21 days. Recovery provides lifelong immunity.
Clinical Disease
Infection is commonest in children aged 4 - 10 years. Infection can also occur in adults and is usually more severe.
Chickenpox usually presents with mild systemic symptoms, and a widespread itchy rash; lesions appear in crops, affecting all regions of the body, including the oropharynx and genitourinary tract, and progress through macules and papules to vesicular eruptions which rupture, crust and spontaneously heal. The rash lasts for about 7 - 10 days.
Complications include:
- Secondary skin infection with S. aureus or S. pyogenes
- Thrombocytopenic purpura
- VZV pneumonitis (high mortality, high risk in immunocompromised and pregnant women)
- Meningitis
- Postinfectious encephalitis
- Congenital varicella syndrome
- Maternal transmission with severe neonatal infection
After primary infection, VZV remains latent in sensory ganglia and in about 20% of patients will reactivate resulting in shingles, a painful vesicular rash in the related dermatome. Ocular damage may follow involvement of the ophthalmic division of the trigeminal nerve. Shingles usually affects older people and the immunocompromised. Shingles lesions are infectious to non-immune individuals who are at risk of developing chickenpox. Shingles can not be contracted directly from individuals with chickenpox, or from other cases of shingles. Up to 10% of shingles episodes will be followed by postherpetic neuralgia.
Diagnosis
Chickenpox and shingles are usually diagnosed clinically, but laboratory diagnosis can be made with NAAT, microscopy, culture and serology.
Treatment
Chickenpox:
For otherwise healthy children and adults:
- If serious complications (such as pneumonia, encephalitis, or dehydration, or severe secondary bacterial infection of the skin) are suspected, admit to hospital.
- Antiviral treatment:
- Consider prescribing oral aciclovir 800 mg 5 times a day for 7 days for an immunocompetent non-pregnant adult or adolescent (aged 14 years or older) with chickenpox who presents within 24 hours of rash onset, particularly for people with severe chickenpox or those at increased risk of complications, such as smokers.
- Aciclovir is not recommended for otherwise healthy children with chickenpox.
- Symptomatic treatment:
- Paracetamol if pain or fever are causing distress (avoid nonsteroidal anti-inflammatory drugs)
- Topical calamine lotion to alleviate itch
- Chlorphenamine for treating itch associated with chickenpox for people 1 year of age or older
N.B. Chickenpox in pregnant women or immunocompromised patients requires specialist input.
Shingles:
In herpes zoster (shingles) systemic antiviral treatment can reduce the severity and duration of pain, reduce complications, and reduce viral shedding. Treatment with the antiviral should be started within 72 hours of the onset of rash and is usually continued for 7–10 days. Immunocompromised patients at high risk of disseminated or severe infection should be treated with a parenteral antiviral drug.
Chronic pain which persists after the rash has healed (postherpetic neuralgia) requires specific management.
Prevention
Although the usual exclusion period is 5 days, all lesions should be crusted over before children return to nursery or school.
Non-immune individuals who have been exposed to chickenpox and are at special risk of complications (e.g. neonates, pregnant women and immunocompromised individuals) may require post-exposure prophylaxis.
A live attenuated-virus vaccine is available and recommended for non-immune healthcare workers.
Chickenpox
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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 |
