Dengue and calcium.

Dengue is potentially fatal unless managed appropriately. No specific treatment is available and the mainstay of treatment is fluid management with careful monitoring, organ support, and correction of metabolic derangement. Evidence with regards to the role of calcium homeostasis in dengue is limited. Low blood calcium levels have been demonstrated in dengue infection and hypocalcemia maybe more pronounced in more severe forms. The cause of hypocalcemia is likely to be multifactorial. Calcium has been also implicated in the immuopathogenesis of dengue; however, the precise clinical implications of these interactions are yet not clearly defined. Derangements of calcium homeostasis are likely to be associated with myocardial dysfunction and cardiac arrhythmias observed in dengue as suggested by in vitro studies. Calcium also plays a role in platelet aggregation. Studies evaluating the therapeutic use of calcium in dengue have been underpowered and poorly designed to make any firm recommendations. Further studies are needed to explore the role and usefulness of maintenance of calcium homeostasis in modulating cardiac dysfunction, immunopathogenesis, and platelet abnormalities related to dengue.

INTRODUCTION

Dengue is endemic in over 100 countries. Infection with the dengue virus may be asymptomatic or may give rise to a spectrum of clinical illness, ranging from undifferentiated fever to a severe life threatening hemorrhagic/shock syndrome with multiple organ failure and fatality. Early recognition of dengue with prompt and appropriate treatment is vital to limit morbidity and mortality.[1] Recent guidelines,[2] which have built on the wealth of experience in managing these patients over recent years have made management strategies more well defined. In brief, the mainstay of management of dengue is based on careful fluid management and monitoring, together with provision of organ support and correction of metabolic derangement where necessary. No specific treatment is available, although steroids and immunoglobulins have been used in the past with little evidence-based benefit.

Hypocalcemia has been documented in dengue infection[345] and is seen more frequently in patients with severe dengue.[4] Nonetheless, evidence with regards to the role of calcium homeostasis in dengue is limited, and current recommendations do not mention the need to monitor or correct blood calcium levels in dengue. In this paper, we discuss the key issues in relation to calcium and dengue infection, focusing on the current evidence on the role of calcium, both intracellular and extracellular, in the pathophysiology and complications of dengue; the causes and effects of low blood calcium levels and the potential place for correction of low calcium levels as well as calcium supplementation as a treatment for dengue infection. Further, we attempt to identify gaps in the understanding of the relationship between calcium homeostasis and dengue infection and suggest key target areas for future basic sciences and clinical research.

MATERIALS AND METHODS

Pubmed was searched for papers containing the keywords ‘dengue’ with any of the following: ‘Calcium’, ‘hypocalcemia’, and ‘hypocalcaemia’ in any combination in the title, abstract, or medical subject headings (MeSH) terms. The search was not time restricted. There were 37 abstracts found during the search. Endnote X5® was used to filter the papers. All authors read through all 37 papers; the full text was read through in these. Related references were also included. Twenty papers provided relevant information regarding the role of calcium pertaining to calcium homeostasis, immunopathogenesis, cardiac dysfunction, and treatment of dengue.

Hypocalcemia in dengue

Hypocalcemia has been demonstrated in other tropical diseases, such as leptospirosis and malaria, and is more commonly seen in severe infection; however, the clinical effects of low blood calcium levels in these conditions are unclear.[6] Several causes for low blood calcium levels have been suggested, including reduced Na+-K adenosine triphosphatase (ATPase) activity, reduced Ca2+-ATPase activity, acquired parathyroid hormone deficiency, renal one-alpha hydroxylase insufficiency, reduced dietary vitamin D intake, and reduced dietary calcium intake.[7] Low blood calcium levels have been demonstrated in dengue infection[3458] and maybe present in over 80% of patients.[3] It is often underrecognized but can present with tetany.[8] There is little information on the other effects of hypocalcemia, e.g., effects on cardiac rhythm and contractility. There is some evidence that hypocalcemia maybe more pronounced in more severe forms of dengue,[4] although lower calcium levels have not shown an association with mortality.[3]

The possible role of calcium in the immuopathogenesis of dengue

In in vitro studies, depletion of Mg2+ and Ca2+ has been shown to enhance binding of dengue virus to monocyte macrophages and cells of T cell and B cell lineages.[9] Ca2+ has been shown to be essential for cytotoxic activity of the dengue type 2 virus (DV)-induced macrophage cytotoxin (CF2); cell death has been shown to be associated with increased intracellular Ca2+.[1011] Ca2+ appears to play a role in the induction of dengue-specific T-helper cells. Dengue antigen has been shown to increase the influx of Ca2+ into T-cells. The proliferation of dengue-specific T-helper cells appears to be dependent on Ca2+ and is inhibited in the absence of Ca2+ and by calcium channel antagonist drugs.[12] In another in vitro study, production of DV-induced suppressor cytokine (SF) by cultured spleen cells was inhibited when the medium was depleted of calcium; production was restored by addition of calcium to the medium. Both the production of SF and transmission of the suppressor signal via syngeneic macrophage (M phi) to recruit the second subpopulation of suppressor T (TS2) cell were inhibited in a dose-dependent manner by the calcium channel antagonists verapamil and nifedipine.[13] There is some evidence that the production of nitrite in response to dengue virus infection is also calcium dependent and can be inhibited by calcium channel blocking drugs.[1415] Thus, calcium appears to play a role in the immune response in dengue, although the interactions are complex, and the precise clinical implications of these interactions are yet not clearly defined.

Calcium and the myocardium in dengue

Calcium plays a key role in the functioning of myocardial tissue. Cardiac involvement in dengue has been documented in many studies, although little is known about its actual pathogenesis.[1617] Dengue myocarditis may present with a variety of features including electrocardiographic changes (sinus bradycardia, tachycardia, T-wave inversions of electrocardiography (ECG)), pericardial effusion, impairment of diastolic function, and pathologically elevated levels of creatine phosphokinase myocardial band (CPK-MB). It has been proposed that the derangements of Ca2+ storage in the infected myocardial cells may directly contribute to the development of myocarditis. Salgado et al.,[18] attempted to test the hypothesis that striated muscle is a target of dengue infection and that alterations in calcium homeostasis was associated with myocardial dysfunction in dengue infection. In this in vitro study, human skeletal myotubes were exposed to dengue virus in vitro and intracellular Ca2+ changes were assayed. Dengue virus capsid proteins were demonstrated in myotubes by confocal immunofluorescence microscopy, confirming virus infection and replication in myotubes. An increase in resting intracellular Ca2+ was demonstrated in infected skeletal myotubes when compared with non-exposed controls. The authors suggested that this increase in resting (i.e. diastolic) Ca2+ levels in infected myocardium may be responsible for arrhythmias and altered contractile function.

The potential role of calcium in treatment of dengue

Calcium is needed for platelet aggregation, although its precise role is not known.[1920] In a case series of just five patients suffering from dengue fever, the administration of oral calcium carbonate and vitamin D3 were reported to result in improvement in clinical condition and platelet counts. However, there was no control group. Platelet counts and clinical features improve spontaneously in dengue; thus these findings are insufficient to conclude that improvement was a result of the intervention.[21] In a case controlled study of 10 patients with clinical features of dengue in each arm, a significant increase in the platelet counts was observed following oral administration of calcium carbonate. Significant clinical improvement, with shorter time to defervescence and clinical recovery was also seen in the treatment arm.[22] Overall, there is no hard evidence of benefit that calcium supplementation is beneficial in dengue, although the limited evidence suggests that it is an area needing further study.

CONCLUSIONS

Hypocalcemia is seen in cases with severe dengue and has been purported to be associated with increased mortality. In vitro studies on animals and human tissue link calcium with the infectivity of dengue virus and the immune response to dengue. Intracellular calcium derangements have been linked with myocarditis and dengue-related cardiac dysfunction. Nonetheless, there is a paucity of clinical evidence on the role of calcium disequilibrium in dengue, the clinical effects of hypocalcemia in dengue and on the interactions between blood calcium ions and the immunopathogenesis of the disease. Although hypocalcemia has been observed in dengue, there is no evidence currently that this hypocalcemia has significant clinical implications. There is little evidence on the role, if any, of calcium replacement in patients with dengue who are hypocalcemic. The potential role of calcium as therapy to modulate the immune system, in either hypocalcemic or normocalcemic patients with dengue is unknown. Though the routine use of calcium in patients with dengue fever cannot be routinely recommended, maintenance of calcium homeostasis in critical dengue patients should be decided on a case by case basis by experienced clinicians. Further well-designed studies are needed in this area that has not been adequately addressed to date. We suggest the following target areas for research:

Clinical studies to identify the incidence and clinical effects of hypocalcemia, in particular, effects on skeletal and cardiac muscle

Basic sciences research aimed at understanding the effects of hypocalcemia on the immune response in dengue

Adequately powered randomized controlled trials of calcium, given intravenously or orally, in patients with dengue associated with hypocalcemia and normocalcemia, with clinical recovery, prevention of shock, and improvement in thrombocytopenia as outcome measures.