Introduction
Dengue infections are one of the most rapidly emerging mosquito-borne
viral infections in the world. It was estimated that 18% of the 58.4
million symptomatic cases of dengue were admitted to hospital in 2013,
which is a staggering 10.5 million patients(1). Approximately 26% to
33.6% of hospitalized patients have shown to develop dengue
haemorrhagic fever (DHF), while 0.6% to 1.5% require admission to the
intensive care units(2-4). As 70% of dengue infections occur in Asia,
dengue causes a huge burden to resource-poor economies in developing
countries(5). Although the recent case fatality rates in many countries
have declined to <0.5% due to intense monitoring and
meticulous fluid management, the case fatality rates are still around
2.6% in some countries such as India(6). Therefore, there is an urgent
need to develop biomarkers which can identify patients who will develop
severe disease and effective drugs to treat dengue.
Endothelial dysfunction leading to vascular leak in the hallmark of
DHF(7). Plasma leakage leads to accumulation of fluid in pleural and
peritoneal cavities, and when severe, it causes reduction of blood
pressure leading in poor organ perfusion resulting in shock and organ
dysfunction. Many inflammatory cytokines, lipid mediators and secretory
virus protein NS1 has been shown to contribute to the vascular
leakage(8-11). The dengue virus (DENV) has been shown to activate mast
cells, and the vascular leak in dengue mouse models has been shown to be
mast cell dependent(12). Mast cell stabilizing drugs such as cromolyn
and ketotifen and the leukotriene inhibitor montelukast, significantly
reduced the vascular leak in dengue mouse models, implying their role in
dengue pathogenesis.
We have previously shown that many inflammatory lipid mediators such as
platelet activating factor (PAF) and secretory phospholipase A2 levels
were higher in patients with DHF, and that endothelial dysfunction
induced by dengue sera was inhibited by PAF-R blockers, in vitro, which
also showed a tend towards a reduction in vascular leakage in patients
with acute dengue(2, 9, 13). Leukotrienes are another group of
inflammatory lipid mediators that are produced by the action of
lipoxygenase enzymes on arachidonic acid substrates, and include LTB4,
LTC4, LTD4 and LTE4 (14). These mediators are potent chemoattractants to
neutrophils and eosinophils, and some are also known to increase
vascular permeability and induce vascular leak (14, 15). LTE4
specifically has been shown to induce vascular leak, specifically by
contracting the endothelial cells in the post-capillary venules(16).
Serum leukotriene B4 levels were shown to be elevated in a small cohort
of patients with acute dengue infection, when compared to healthy
individuals and other febrile illnesses and correlated with inflammatory
markers such as highly sensitive CRP(17). In vitro experiments have also
shown that the DENV induced LTB4 from neutrophils, suggesting that there
could be multiple sources of leukotrienes in acute dengue infection.
However, if leukotrienes correlate with clinical disease severity,
viraemia and serostatus and the relationship with the onset of vascular
leak in acute dengue has not been investigated.
Currently all individuals who have warning signs of possible severe
disease such as persistent vomiting, abdominal pain, leucopenia along
with thromobocytopenia are admitted to the hospital(18). However, only
25% to 34% of such patients would develop complications such as DHF
and organ dysfunction(2, 4, 19). The onset of plasma leakage usually
occurs during 3 to 6 days and lasts for 24 to 48 hours, which is known
as the critical phase(7, 18). Those who do not develop vascular leak
have a self-limiting illness known as dengue fever, and usually recover
without any intervention, except if accompanied by bleeding
manifestations. However, due to the absence of a reliable biomarker, all
patients who are admitted should be closely monitored, several times a
day, which is a huge burden in overcrowded hospital facilities with
limited staff. Several potential biomarkers have been identified such as
serum chymase, serotonin, VEGF and tryptase levels(20-23). However, it
would be useful to evaluate a urinary biomarker to predict the
development of DHF during early illness as it would user friendly.
Urinary LTE4 has been shown to be a stable metabolite in urine and spot
urine LTE4 levels have been evaluated as a diagnostic marker of atopic
asthma in pre-school children.(24) In this study we evaluated the levels
of urinary LTE4 and histamine in a large cohort of patients with varying
severity of acute infection during early illness, their kinetics
throughout the illness and also diurnal variations. We investigated the
relationship between the urinary LTE4 levels, with the onset of vascular
leakage, viral loads and serostatus.