The authors have declared that no competing interests exist.
At the end of 2005, an outbreak of fever associated with joint pain occurred in La Réunion. The causal agent, chikungunya virus (CHIKV), has been known for 50 years and could thus be readily identified. This arbovirus is present worldwide, particularly in India, but also in Europe, with new variants returning to Africa. In humans, it causes a disease characterized by a typical acute infection, sometimes followed by persistent arthralgia and myalgia lasting months or years. Investigations in the La Réunion cohort and studies in a macaque model of chikungunya implicated monocytes-macrophages in viral persistence. In this Review, we consider the relationship between CHIKV and the immune response and discuss predictive factors for chronic arthralgia and myalgia by providing an overview of current knowledge on chikungunya pathogenesis. Comparisons of data from animal models of the acute and chronic phases of infection, and data from clinical series, provide information about the mechanisms of CHIKV infection–associated inflammation, viral persistence in monocytes-macrophages, and their link to chronic signs.
The major epidemic of chikungunya virus fever (chikungunya) that affected 266,000 people in La Réunion in 2006 highlighted the vulnerability of immunologically naive populations and raised interest in this disease in the media, governments, and the scientific community
An adaptive mutation in the virus led to
Setting | La Réunion and Indian Ocean Islands |
India |
Singapore |
Malaysia |
|
34±20 | 35 (median) | 37(median) | 35.9±18 |
|
0.84 | 0.6 – 0.9 | 3.4 | 0.82 – 1.03 |
|
||||
Fever | 100 | 81 – 100 | 90 | 86 – 100 |
Arthralgia |
100 | 86 – 80 | 88 | 82 – 100 |
Cephalalgia |
70 | 93 | 43 | 30 – 50 |
Myalgia |
64 | 48 – 84 | 61 | 10 – 48 |
Rash | 39 | 36 – 50 | 36 | 64 – 17 – 50 |
Erythema | 33 | — | ||
Asthenia |
67 | 43 | ||
Maculopapular eruption | 33 | 17 | ||
Meningo-encephalitis | 16 | 25 | ||
Diarrhea / vomiting | 18 | 12/4 | 3/8 | |
Renal failure | 20 | — | ||
Respiratory failure | 16 | — | ||
Myocarditis / pericarditis | 6 | 11 | ||
Hepatitis | 6 | — | Yes |
|
Sensory changes (muffling of noise, sensitivity to light) | 9 | 33 | ||
Aphtous-like ulcer | — | 21 | ||
Hyperpigmentation | 15 | 20 | ||
Genital ulcers | — | 1 | ||
Optic neuritis | <1 | <1 | 11 |
|
Facial paralysis | — | 2 | ||
Guillain-Barre syndrome | 1 | Yes |
||
|
||||
Hyperalgia |
27 | Yes |
||
Diarrhea/vomiting | 27 | Yes |
||
Convulsions | 22 | Yes |
||
Bullous dermatosis | 17 | Yes |
||
Purpura | 8 | Yes |
||
Encephalitis | 6 | Yes |
Atypical forms were noticed but their prevalence was not evaluated.
Retro-orbital pain.
We aim here to present current knowledge on CHIKV infection and related aspects, such as the inflammatory response which potentially leads to the development of chronic syndromes.
CHIKV spreads rapidly in the body after initial infection (
Following inoculation with CHIKV through a mosquito bite, the virus directly enters the subcutaneous capillaries, with some viruses infecting susceptible cells in the skin, such as macrophages or fibroblasts and endothelial cells. Local viral replication seems to be minor and limited in time, with the locally produced virus probably being transported to secondary lymphoid organs close to the site of inoculation. The blood carries most viruses, as free virions or in the form of infected monocytes, to the target organs, the liver, muscle, joints, and remote lymphoid organs. In these tissues, infection is associated with a marked infiltration of mononuclear cells, including macrophages, particularly when viral replication occurs. The pathological events associated with tissue infection are mostly subclinical in the liver (hepatocyte apoptosis) and lymphoid organs (adenopathy), whereas mononuclear cell infiltration and viral replication in the muscles and joints are associated with very strong pain, with some of the patients presenting arthritis. * Guillain-Barré syndrome and encephalitis are very rare events. † True arthritis remains a rare event (from 2% to 10%); see
Acute-phase symptoms usually disappear after 2 weeks. However, arthralgia and/or myalgia may persist for weeks, months, or even years. Some patients go on to develop a genuine, chronic arthritic syndrome. Typically, joint damage fluctuates over time, but always affects the same parts of the body, mostly the extremities (hands, ankles, knuckles;
Setting (Date Referred) | La Réunion (2005 to 04/2006) |
La Réunion (04/2006–2007) |
India Karmataka (2008) |
India Maharashtra (2006) |
Singapore (2008) |
|
56 |
116/133 |
94/203 |
59/315 |
14 |
|
60 | 58 (median) | 41 | 48 | 38±6 |
|
0.93 |
0.33 | 0.81 | 0.33 |
1.8 |
|
65.9 | 85 | 0 | 0 | 100 |
|
100 | 100 | 94 | 100 | 100 |
|
NR | NR | 27 | NR | NR |
|
16 | NR | 58.5 | NR | NR |
|
NR | ||||
|
64 | More often | 83 | NR | |
|
21 (57) | 20 | 59.5 | 57 | |
|
29/16 | 31/21 | 54/31 | 15/59 | |
|
30 | NR | 15 | 52.5 | |
|
5 | NR | 11 | 7 | |
|
55 | 68 | NR | 100 | |
|
ND | 10 | 36 |
100 NSA | 0 |
|
ND | 22 | IE | 7 IA | 0 |
|
71 | Not detailed | 10/20 tested by MRI | NR | 0 |
|
51 | 7 | 7 | 5 | 0 |
Low ALT/ASAT level related to persistence (
Lower level of creatinine
No difference chronic versus recovered.
American College of Rheumatology criteria for rheumatoid arthritis in
IA, inflammatory arthritis; IE, inflammatory, erosive; MRI, magnetic resonance imaging; ND, not detected or prevalence not evaluated; NR, not reported; NSA, non-specific arthritis.
Following the 2005–2006 epidemic in La Réunion, 36% of patients reported the persistence of symptoms 15 months after disease onset, and 21% reported at least one recurrence
Persistent symptoms, including arthralgia, myalgia, and arthritis (consistently found on radiological/MRI examination in various sets of patients, see
The mouse was the first organism used for
There is currently no animal model reproducing the chronic rheumatoid syndrome of chikungunya. Indeed, the disease has too short a course in mice
Recent data have clearly implicated inflammatory mediators not only in the acute and resolution phases of chikungunya, but also in the establishment of chronic disease.
(1) Months after the acute infection, monocytes, T cells, and natural killer (NK) cells are still attracted to the inflamed joint, where they become activated. (2) The infection of macrophages in joints is associated with local inflammation and the production of cytokines, chemokines, and pro-inflammatory effectors, such as MCP-1/CCL-2, IL-8, IL-6, IFN-α, and MMP2. (3) The phagocytosis of apoptotic bodies from infected cells probably contributes to viral persistence. Nevertheless, the beneficial or deleterious effect of local inflammation on viral persistence remains unclear. (4) When it occurs, arthritis is accompanied by high rates of fibroblast apoptosis and cartilage destruction. Chronic inflammation probably plays a major role in this damage and associated pain. (5) The potential relationship between local inflammation of the joint and a state of systemic activation, as demonstrated by the presence of inflammation markers in plasma and blood cells, remains unclear.
The first phase of CHIKV infection is typical of acute viral infection, with a very early type 1 interferon (IFN) response
Viral load is related to the concentrations of IFN-α, IL-1-RA, IL-6, MCP-1/CCL-2, IL-12 and IP-10/CXCL-10
The inflammatory response to CHIKV infection leads to viral elimination from the blood and clinical recovery. However, it is now clear that disease may persist in a subgroup of patients presenting variable levels of myalgia and arthralgia, culminating in some cases in a debilitating arthritic syndrome. Five studies have tried to identify the factors associated with chronic chikungunya disease in groups of patients in Singapore
Parameter | Recovered Patients | Chronic Patients | α Risk | Series |
|
50.3±13.7 | 70.7±15.5 | 2% | La Réunion |
40.2±12.3 | 31.5±5.2 | NS | Singapore |
|
34.5 | 41.5 | NS | Dakshina Kannada |
|
Cure rate 10 months after inclusion declining with age | <1‰ | Dakshina Kannada |
||
|
||||
Viral load at inclusion | 2.3×106±3.7×106 cp/ml | 3.9×109±6.9×109 cp/ml | 5‰ | La Réunion |
6.9×107±1.5×108 pfu/ml | 1.12×104±5.2×103 pfu/ml | NS | Singapore |
|
Plasma CRP concentration at inclusion | 11.33±10.05 mg/ml | 60.2±59.7 mg/ml | 7% | La Réunion |
Circulating cytokine concentrations at inclusion | Th1 and Th2, moderate | Trend toward a Th1 bias | NS | La Réunion |
|
||||
Circulating GM-CSF, 2–3 months post inclusion | Normal | Higher than controls | <5% | Singapore |
Circulating eotaxin and HGF, 2–3 months post inclusion | Higher than controls | Normal | <5% | Singapore |
Circulating IL-6, 2–3 months post inclusion | Lower than controls | Normal | <5% | Singapore |
|
||||
Circulating IL-12 p40 post acute phase | Not detectable | Persistent (±1 ng/ml) | 0.5‰ |
La Réunion |
Circulating MIG/CXCL-9 and IP-10/CXCL-10, 6 months post inclusion | Higher in patients with chronic disease than in fully recovered patients | <5% | Emilia Romagna |
|
CHIKV-specific IgG titer, 6 months post inclusion | Higher in patients with chronic disease than in fully recovered patients | <5% | Emilia Romagna |
|
Circulating cytokines, 10–12 months post inclusion | Th2 (increased IL-5) | Th1: IL-1β, IL-1RA, IL-6, MCP-1/CCL-2, MIP-1α/CCL-3, MIP-1β/CCL-4 | <5% | Dakshina Kannada |
No difference between patients with chronic disease and fully recovered patients | NS | Emilia Romagna |
||
IFN-α mRNA in PBMC, 12 months post inclusion | Not detectable | High levels | 2% |
La Réunion |
|
||||
CHIKV detection in the joint at late time points (>12 months) | No | Yes, in macrophages | NA | La Réunion |
Joint inflammation at late time points (>12 months) | No | MCP-1/CCL-2, IL-8, IL-6, MMP2, IFN-α | NA | La Réunion |
Mann and Whitney test performed by us.
Inclusion: first presentation of the patient during acute disease.
Numbers (and sex ratios) of patients with chronic disease were 5 (4) in Singapore, 32 (0.15) in La Réunion, 94 (0.82) in Dakshina Kannada, and 35 (sex ratio not available) in Emilia Romagna.
cp, viral RNA copies; CRP, C reactive protein; NA, not applicable; NS, not significant; pfu, plaque-forming units.
The proportion of patients with chronic signs attributable to CHIKV differed between series. In Singapore, 13% of the infected patients still had chronic arthralgia 3 months after infection
Patients with chronic symptoms differ considerably in acute infection characteristics. Hoarau et al. reported high baseline viral loads in patients with chronic disease (10 versus 2.1×109 copies/ml,
Patient age appeared to be crucial in the La Réunion and Dakshina Kannada groups, but not in Singapore (see
Hoarau et al. also suggested a link between chronic disease and a stronger inflammatory Th1 response to acute infection (
The recovery period lies between the acute and chronic phases. During this period, active regulatory mechanisms responsible for the resolution of inflammation take place. These mechanisms mostly involve macrophages and their unique ability to arouse and regulate inflammation (
Macrophage infiltration, under the control of MCP-1/CCL-2, is a critical feature of damaged tissues. The inflammatory effectors IL-6, IL-8, MCP-1/CCL-2, MMP2, and INF-α are specifically expressed in the tissues of patients with chronic chikungunya, who have high IFN-α and IL-12 mRNA levels in their circulating leukocytes. This classical inflammatory process may be regulated by HGF and eotaxin, which have different expression profiles during the recovery phase in patients with chikungunya, depending on whether or not these patients go on to develop chronic disease. HGF also promotes muscle regeneration. Once they have infiltrated the joint or muscle, the macrophages are activated and regulate the local Th1/Th2 balance as a function of their own activation status (classical/M1 or alternative/M2). GM-CSF and HGF, which have M1 and M2 effector activities, respectively, may modulate this balance as they are differentially expressed in acute and chronic chikungunya. CHIKV persists in infected macrophages only in patients with a chronic rheumatic syndrome. The reciprocal influences connecting viral persistence and local inflammation are not known. Solid arrows: activation. Solid stopped lines: regulation. Dotted arrows: expression.
The recovery phase appears to play a critical role in the establishment of chronic disease, at least in patients from Singapore. Chow et al. found higher GM-CSF (granulocyte-macrophage colony-stimulating factor) concentrations in patients subsequently displaying chronic symptoms than in those who fully recovered and the control group
HGF also has beneficial effects on muscle regeneration
In addition to IL-6, chronic chikungunya (>6 months) is also associated with other systemic markers of inflammation, such as IFN-α
These data highlight the role of macrophages in chronic arthralgia and arthritis as a virus reservoir and as the main local cell type involved in regulating inflammation and Th1/Th2 balance. The central role of macrophages in chronic chikungunya disease and various pathogenic pathways involved are illustrated in
Regulatory mechanisms seem to be required to prevent the establishment of chronic disease weeks or even months after viral clearance from the blood. The absence of such mechanisms leads to chronic arthralgia, or the arthritis observed in the group from La Réunion. Hoarau et al. detected CHIKV and various markers of inflammation (IFN-α, IL-6, MCP-1/CCL-2, IL-8, and MMP2) in the synovium of a patient suffering from chronic pain, but not in synovium of two patients who recovered fully
The persistence of CHIKV in joints may therefore lead to chronic local inflammation, causing pain. Local inflammation would in turn establish local conditions favoring CHIKV persistence. Indeed, we know from HIV/AIDS studies
Hoarau et al. reported high plasma concentrations of IL-12 and IFN-α mRNA in blood mononuclear cells after the convalescence phase, in patients with chronic disease, between 6 months and 1 year after infection. In the patients from Singapore, the concentrations of these two cytokines, measured by alternative techniques, peaked in the acute phase and returned to normal levels at 2–3 months, even in patients who still had clinical symptoms. Consistent with the findings of Hoarau et al., Kelvin et al. and Chaaithanya et al. reported high levels of Th1-type cytokines in the blood of patients with chronic disease (see
Sissoko D, Malvy D, Ezzedine K, Renault P, Moscetti F, et al. (2009) Post-epidemic chikungunya disease on Reunion Island: course of rheumatic manifestations and associated factors over a 15-month period. PLoS Negl Trop Dis 3: e389. doi:10.1371/journal.pntd.0000389
Gardner J, Anraku I, Le TT, Larcher T, Major L, et al. (2010) Chikungunya virus arthritis in adult wild-type mice. J Virol 84: 8021–8032.
Labadie K, Larcher T, Joubert C, Mannioui A, Delache B, et al. (2010) Chikungunya disease in nonhuman primates involves long-term viral persistence in macrophages. J Clin Invest 120: 894–906.
Chow A, Her Z, Ong EK, Chen JM, Dimatatac F, et al. (2011) Persistent arthralgia induced by chikungunya virus infection is associated with interleukin-6 and granulocyte macrophage colony-stimulating factor. J Infect Dis 203: 149–157.
Hoarau JJ, Jaffar Bandjee MC, Trotot PK, Das T, Li-Pat-Yuen G, et al. (2010) Persistent chronic inflammation and infection by chikungunya arthritogenic alphavirus in spite of a robust host immune response. J Immunol 184: 5914–5927.
Chronic signs of chikungunya disease.
What animal models tell about chikungunya virus persistence.
Relationship between inflammatory response to infection and chronic rheumatic syndrome.