Sir,

Dengue fever (DF) by any one of the four serotypes (DEN-1 through -4) produces life-long immunity against re-infection by that same serotype but only temporary and partial protection against other serotypes.1 We report a case of recurrent, bilateral dengue-related chorioretinopathy with two different dengue serotypes.

Case report

A 39-year-old Chinese female contracted DF serotype DEN-3 confirmed by polymerase chain reaction (PCR) on day 3 of her illness. Seven days after the onset of fever (platelet nadir 33 × 109/l), she complained of bilateral blurring of vision. Vision was 6/120 in the right and CF in the left. Posterior segment revealed macular cotton-wool spots, bilateral flame haemorrhages, and macula oedema with vascular sheathing (Figure 1. Optical coherence tomography showed cystic oedema of 607 and 825 μm for right and left respectively. Fluorescein angiogram demonstrated vascular leakage in all quadrants including maculae, retinal periphlebitis with right macular branch vein occlusion and severe macula oedema.

Figure 1
figure 1

Posterior segment photographs showing cotton wool spots, flame haemorrhages, macula oedema and vascular sheathing in both maculae.

Full size image

Subjectively, her vision and metamorphopsia improved spontaneously. Macular oedema resolved within 4 weeks and visual acuity returned to 6/6 by 13 weeks. The posterior uveitis and vasculitis resolved over 6 months leaving a persistent, non-progressive paracentral relative scotoma.

A year later, she developed another episode of DF with visual disturbance on the fifth day after the onset. Vision was 6/6 with mild macular oedema. Visual field assessment showed a central scotoma on the right and patchy defects on the left eye—both larger than that seen previously. Enzyme-linked immunosorbent assay-based serotyping performed on day 8 after the onset of her illness revealed antibodies to both DEN-2 and -3 strains, indicating a second infection with the DEN-2 strain (serologic studies during the first episode did not reveal any antibodies to DEN-2). Her symptoms resolved but scotomata persisted up till 2 years later.

Comment

Our patient initially developed bilateral dengue-related posterior uveitis and vasculitis caused by DEN-3 serotype. Her clinical course is consistent with previous reports of resolution without treatment.2, 3, 4, 5 However, she developed a relapse following re-infection with a different serotype (DEN-2). The different investigative methods were chosen based on the number of days after onset of her illness in each episode. PCR has high sensitivity in the first few days of illness but this drops off to about 50% on day 5/6 and rapidly falls after that. Serology requires the body to produce antibodies, which become detectable in 50% by about the sixth day of illness. Hence, PCR is best in early disease and serology is better in later disease. Systemic infection by one serotype provides partial protection against other serotypes, thus subsequent infections are possible. These tend to be more severe and more likely to cause dengue haemorrhagic fever.6 Similarly, posterior uveitis that follows an infection by one serotype is not ‘protective’ and can relapse in subsequent infections with other serotypes. However, unlike recurrent systemic infections, these are not more severe than the first episode but may cause enlargement of residual functional scotomata.