Clinical, epidemiological, and spatial features of human rabies cases in Metro Manila, the Philippines from 2006 to 2015.

Rabies remains a public health problem in the Philippines despite the widespread provision of rabies vaccines and rabies immunoglobulin (RIG) as post-exposure prophylaxis (PEP). Detailed descriptions of recent human rabies cases in the Philippines are scarce. This study aimed to describe the clinical, epidemiological, and spatial features of human rabies cases between January 1, 2006, and December 31, 2015. We conducted a retrospective hospital-based case record review of all patients admitted to one referral hospital in Manila who received a clinical diagnosis of rabies. During the 10-year study period there were 575 patients (average 57.5 cases per year, range 57 to 119) with a final diagnosis of rabies. Most patients were male (n = 404, 70.3%) and aged ≥ 20 years (n = 433, 75.3%). Patients mostly came from the National Capital Region (n = 160, 28.0%) and the adjacent Regions III (n = 197, 34.4%) and IV-A (n = 168, 29.4%). Case mapping and heatmaps showed that human rabies cases were continuously observed in similar areas throughout the study period. Most patients had hydrophobia (n = 444, 95.5%) and/or aerophobia (n = 432, 93.3%). The leading causative animals were dogs (n = 421, 96.3%) and cats (n = 16, 3.7%). Among 437 patients with animal exposure history, only 42 (9.6%) had been administered at least one rabies vaccine. Two patients (0.5%), young children bitten on their face, had received and a full course of rabies vaccine. Human rabies patients were continuously admitted to the hospital, with no notable decline over the study period. The geographical area in which human rabies cases commonly occurred also did not change. Few patients received PEP and there were two suspected cases of PEP failure. The retrospective design of this study was a limitation; thus, prospective studies are required.

The non-linear and lagged short-term relationship between rainfall and leptospirosis and the intermediate role of floods in the Philippines.

BACKGROUND: Leptospirosis is a worldwide bacterial zoonosis. Outbreaks of leptospirosis after heavy rainfall and flooding have been reported. However, few studies have formally quantified the effect of weather factors on leptospirosis incidence. We estimated the association between rainfall and leptospirosis cases in an urban setting in Manila, the Philippines, and examined the potential intermediate role of floods in this association. METHODS/PRINCIPAL FINDINGS: Relationships between rainfall and the weekly number of hospital admissions due to leptospirosis from 2001 to 2012 were analyzed using a distributed lag non-linear model in a quasi-Poisson regression framework, controlling for seasonally varying factors other than rainfall. The role of floods on the rainfall-leptospirosis relationship was examined using an indicator. We reported relative risks (RRs) by rainfall category based on the flood warning system in the country. The risk of post-rainfall leptospirosis peaked at a lag of 2 weeks (using 0 cm/week rainfall as the reference) with RRs of 1.30 (95% confidence interval: 0.99-1.70), 1.53 (1.12-2.09), 2.45 (1.80-3.33), 4.61 (3.30-6.43), and 13.77 (9.10-20.82) for light, moderate, heavy, intense and torrential rainfall (at 2, 5, 16, 32 and 63 cm/week), respectively. After adjusting for floods, RRs (at a lag of 2 weeks) decreased at higher rainfall levels suggesting that flood is on the causal pathway between rainfall and leptospirosis. CONCLUSIONS: Rainfall was strongly associated with increased hospital admission for leptospirosis at a lag of 2 weeks, and this association was explained in part by floods.

Building prognostic models for adverse outcomes in a prospective cohort of hospitalised patients with acute leptospirosis infection in the Philippines.

Leptospirosis is endemic to the Philippines. Ten per cent of cases will develop severe or fatal disease. Predicting progression to severity is difficult. Risk factors have been suggested, but few attempts have been made to create predictive models to guide clinical decisions. We present two models to predict the risk of mortality and progression to severe disease. Data was used from a prospective cohort study conducted between 2011 and 2013 in San Lazaro Hospital, Manila. Predictive factors were identified from a literature review. A strategy utilizing backwards stepwise-elimination and multivariate fractional polynomials identified key predictive factors. A total of 203 patients met the inclusion criteria. The overall mortality rate was 6.84%. Multivariable logistic regression revealed that neutrophil counts [OR 1.38, 95% CI 1.15-1.67] and platelet counts [OR 0.99, 95% CI 0.97-0.99] were predictive for risk of mortality. Multivariable logistic regression revealed that male sex (OR 3.29, 95% CI 1.22-12.57) and number of days between symptom onset and antibiotic use (OR 1.28, 95% CI 1.08-1.53) were predictive for risk of progression to severe disease. The multivariable prognostic models for the risks of mortality and progression to severe disease developed could be useful in guiding clinical management by the early identification of patients at risk of adverse outcomes.

Diagnostic Accuracy of Recombinant Immunoglobulin-like Protein A-Based IgM ELISA for the Early Diagnosis of Leptospirosis in the Philippines.

BACKGROUND: Leptospirosis is an important but largely under-recognized public health problem in the tropics. Establishment of highly sensitive and specific laboratory diagnosis is essential to reveal the magnitude of problem and to improve treatment. This study aimed to evaluate the diagnostic accuracy of a recombinant LigA protein based IgM ELISA during outbreaks in the clinical-setting of a highly endemic country. METHODOLOGY/PRINCIPAL FINDINGS: A prospective study was conducted from October 2011 to September 2013 at a national referral hospital for infectious diseases in Manila, Philippines. Patients who were hospitalized with clinically suspected leptospirosis were enrolled. Plasma and urine were collected on admission and/or at discharge and tested using the LigA-IgM ELISA and a whole cell-based IgM ELISA. Sensitivity and specificity of these tests were evaluated with cases diagnosed by microscopic agglutination test (MAT), culture and LAMP as the composite reference standard and blood bank donors as healthy controls: the mean+3 standard deviation optical density value of healthy controls was used as the cut-off limit (0.062 for the LigA-IgM ELISA and 0.691 for the whole cell-based IgM ELISA). Of 304 patients enrolled in the study, 270 (89.1%) were male and the median age was 30.5 years; 167 (54.9%) were laboratory confirmed. The sensitivity and ROC curve AUC for the LigA-IgM ELISA was significantly greater than the whole cell-based IgM ELISA (69.5% vs. 54.3%, p<0.01; 0.90 vs. 0.82, p<0.01) on admission, but not at discharge. The specificity of LigA-IgM ELISA and whole cell-based IgM ELISA were not significantly different (98% vs. 97%). Among 158 MAT negative patients, 53 and 28 were positive by LigA- and whole cell-based IgM ELISA, respectively; if the laboratory confirmation was re-defined by LigA-IgM ELISA and LAMP, the clinical findings were more characteristic of leptospirosis than the diagnosis based on MAT/culture/LAMP. CONCLUSIONS/SIGNIFICANCE: The newly developed LigA-IgM ELISA is more sensitive than the whole cell-based IgM based ELISA. Although the final diagnosis must be validated by more specific tests, LigA-IgM ELISA could be a useful diagnostic test in a real clinical-setting, where diagnosis is needed in the early phase of infection.

Demographic, clinical and laboratory findings among adult and pediatric patients hospitalized with dengue in the Philippines.

We evaluated the differences in demographic, clinical, and laboratory findings between adult and pediatric patients hospitalized with dengue fever. Ninety patients with dengue infection admitted at San Lazaro Hospital (SLH), Manila from September 2005 to January 2006 were included in the study. The cases were laboratory-confirmed to have dengue infection. The majority of dengue cases (92%) had secondary dengue infection (median age = 18, age range: 2-37) while the remainder (8%) had a primary dengue infection (median age = 12, age range: 7-22). Nearly all the patients (99%) had dengue hemorrhagic fever (DHF). Sixty-five of the cases (72%) had serotype data: 2 (3%) were dengue virus serotype 1 (DENV-1) (median age = 17), 12 (18%) had DENV-2 (median age = 17.5), 38 (59%) had DENV-3 (median age = 16) and 13 (20%) had DENV-4 (median age = 18). The initial signs, symptoms and laboratory results except hematocrit (p = 0.02) and hemoglobin (p = 0.02) did not differ significantly between adults and children. During the study period, half the cases were adults (218 years; n = 45) and half were children (<18 years; n = 45). The ages of cases ranged from 2 to 37 years (median = 17 years) and the peak incidence was 15-19 years. Dengue is often considered as a pediatric disease. Additional studies are needed to determine if an age shift is occurring and where.

Elevated levels of full-length and thrombin-cleaved osteopontin during acute dengue virus infection are associated with coagulation abnormalities.

INTRODUCTION: Dengue virus (DENV) is transmitted by the mosquito vector, and causes a wide range of symptoms that lead to dengue fever (DF) or life-threatening dengue hemorrhagic fever (DHF). The host and viral correlates that contribute to DF and DHF are complex and poorly understood, but appear to be linked to inflammation and impaired coagulation. Full-length osteopontin (FL-OPN), a glycoprotein, and its activated thrombin-cleaved product, trOPN, integrate multiple immunological signals through the induction of pro-inflammatory cytokines. MATERIALS AND METHOD: To understand the role of OPN in DENV-infection, we assessed circulating levels of FL-OPN, trOPN, and several coagulation markers (D-dimer, thrombin-antithrombin complex [TAT], thrombomodulin [TM], and ferritin in blood obtained from 65 DENV infected patients in the critical and recovery phases of DF and DHF during a dengue virus epidemic in the Philippines in 2010. RESULTS: Levels of FL-OPN, trOPN, D-dimer, TAT, and TM were significantly elevated in the critical phase in both the DF and DHF groups, as compared with healthy controls. During the recovery phase, FL-OPN levels declined while trOPN levels increased dramatically in both the DF and DHF groups. FL-OPN levels were directly correlated with D-dimer and ferritin levels, while the generation of trOPN was associated with TAT levels, platelet counts, and viral RNA load. CONCLUSION: Our study demonstrated the marked elevation of plasma levels of FL-OPN and thrombin-cleaved OPN product, trOPN, in DENV-infection for the first time. Further studies on the biological functions of these matricellular proteins in DENV-infection would clarify its pathogenesis.

Safety and immunogenicity of purified vero cell rabies vaccine versus purified chick embryo cell rabies vaccine using pre-exposure and post exposure regimen among healthy volunteers in San Lazaro Hospital

OBJECTIVE: This is a prospective, randomized open-labeled clinical study to demonstrate the safety and immunogenicity of Purified Vero Cell Rabies Vaccine (PVRV) Freeze-Dried using pre-exposure and post- exposure regimen utilizing Modified Thai Red Cross schedule (Modified TRC) in comparison with Purified Chick Embryo Cell (PCEC) Rabies Vaccine among healthy volunteers in San Lazaro Hospital.METHODOLOGY: A total of 189 healthy Filipino volunteers were randomized into three groups: Group A received PVRV 0.1 ml intradermally (ID) using the pre-exposure regimen (Day 0, 7, 28). Group B and Group C were given PVRV 0.1 ml ID and PCEC 0.1 ml ID, respectively, using the Modified TRC on days 0, 3, 7 and 30. The statistical tables and graphs were generated using Microsoft® Excel® 2010. SPSS® version 13 for Windows™ was used for descriptive statistics (geometric mean, arithmetic mean, standard deviation and percentages) and inferential statistics (?2 test, one-way ANOVA and two-way mixed factorial ANOVA).RESULTS: The results revealed that the percentage seroconversion of both PRVR and PCEC post-exposure groups in this clinical study were 100% on days 14 and 90. The PRVR pre-exposure group achieved 96% seroconversion on Day 28 with Geometric Mean titers (GMT) of 1.96 IU/ml (95% CI: 1.45 - 2.65), which is comparable to other similar studies on pre-exposure rabies vaccination. There was no overall difference in all three groups for the whole duration of the study (p = 1.000). The geometic mean titers (GMT) for post-exposure PRVR and PCEC groups on days 14, 30 and 90 were all above 0.5 IU/ml. There was no significant difference between these two post-exposure groups (p = 0.052). The proportion of the subjects in the three groups who experienced local (pain and tenderness at the injection sites, erythema and itching) or systemic reactions (low grade fever, dizziness and headache) during follow-up period were not significantly different (p = 0.134). There were no serious adverse events (SAEs) reported during the follow-up period.CONCLUSION: The Asian manufactured PVRV is safe, tolerable, immunogenic and comparable with PCEC and therefore, the Asian manufactured PVRV can be an economical alternative for rabies post-exposure treatment using the modified TRC regimen and for pre-exposure prophylaxis.

An evaluation of the safety and potency of equine rabies immunoglobulin through measurement of suppression on vaccine-induced antibody production among healthy volunteers

OBJECTIVE: This study evaluated the safety and potency of a new highly purified equine rabies immunoglobulin (ERIG) through indirect measurement of suppression of vaccine-induced antibody production using rapid fluorescent focus inhibition test.METHODOLOGY: This is a prospective, randomized open labeled clinical study on healthy volunteers. Forty-five subjects were randomly assigned to three groups of 15 subjects: All groups received the purified chick embryo cell culture (PCEC) rabies vaccine using the Zagreb regimen (2-1-1). Group A then received ERIG at the same site where the PCEC vaccine was administered; Group B received ERIG at a distant site from where the PCEC vaccine was administered; Group C received only the PCEC vaccine at the same regimen. Arithmetic mean (AM), standard deviation (SD) and range were used to describe the baseline characteristics. Geometric mean titer (GMT) was calculated on Days 0, 7, 14, 21 and 28. Wilcoxon rank-sum test and Kruskall-Wallis Analysis of Variance test were used to compare the means of two and three groups, respectively. Local and systemic adverse reactions were reported by subjects and monitored by investigators.RESULTS: By day 14, 64% of the subjects in Group A, 20% in Group B and 7.0% in Group C failed to seroconvert. During that same period, comparative analysis of GMT of Group A (0.36, 95% CI: -17.92 to 18.64), Group B (1.09, 95% CI: 0.14 to 2.04) and Group C (3.90, 95% CI: -0.63 to 8.43) showed statistically significant differences (p = 0.0016). In terms of safety, neither serious adverse events nor anaphylactic reactions were reported.CONCLUSION: ERIG is a potent and safe product that can be effectively used for passive immunization in category III rabies exposures. In resource-limited areas, this product is an excellent alternative to human rabies immunoglobulin (HRIG).

Galectin-9 plasma levels reflect adverse hematological and immunological features in acute dengue virus infection.

BACKGROUND: Dengue virus (DENV) infection remains a major public health burden worldwide. Soluble mediators may play a critical role in the pathogenesis of acute DENV infection. Galectin-9 (Gal-9) is a soluble ß-galactoside-binding lectin, with multiple immunoregulatory and inflammatory properties. OBJECTIVE: To investigate plasma Gal-9 levels as a biomarker for DENV infection. STUDY DESIGN: We enrolled 65 DENV infected patients during the 2010 epidemic in the Philippines and measured their plasma Gal-9 and cytokine/chemokine levels, DENV genotypes, and copy number during the critical and recovery phases of illness. RESULTS: During the critical phase, Gal-9 levels were significantly higher in DENV infected patients compared to healthy or those with non-dengue febrile illness. The highest Gal-9 levels were observed in dengue hemorrhagic fever (DHF) patients (DHF: 2464 pg/ml; dengue fever patients (DF): 1407 pg/ml; non-dengue febrile illness: 616 pg/ml; healthy: 196 pg/ml). In the recovery phase, Gal-9 levels significantly declined from peak levels in DF and DHF patients. Gal-9 levels tracked viral load, and were associated with multiple cytokines and chemokines (IL-1α, IL-8, IP-10, and VEGF), including monocyte frequencies and hematologic variables of coagulation. Further discriminant analyses showed that eotaxin, Gal-9, IFN-α2, and MCP-1 could detect 92% of DHF and 79.3% of DF, specifically (P<0.01). CONCLUSION: Gal-9 appears to track DENV inflammatory responses, and therefore, it could serve as an important novel biomarker of acute DENV infection and disease severity.

Hospital-based surveillance of Japanese encephalitis at a tertiary hospital in Manila.

Japanese encephalitis virus (JEV) is endemic in the Philippines but the incidence and burden of disease are not well established. We conducted a prospective hospital-based study at San Lazaro Hospital, a tertiary level hospital in Manila, from September 2005 to December 2006. Cases were determined using an in-house dengue and Japanese encephalitis (JE) enzyme-linked immunosorbent assay in order to detect the proportion of JE cases among the acute encephalitis syndrome (AES) cases admitted to our hospital. Fifteen patients were found to have AES, of whom 6 (40%) had confirmed JE. Of the JE cases, 4 were females and 2 were males with an age range of 3-14 years. Three of the 6 JE cases occurred during July. The most common signs and symptoms on admission among JE cases were: fever, headache, loss of appetite, neck rigidity and altered sensorium. JE likely comprises a significant proportion of hospitalized AES cases among children from Manila and nearby provinces. Further studies on the nation-wide prevalence and distribution of JE in the Philippines are needed to guide health authorities in disease control and prevention strategies.

Platelet apoptosis and apoptotic platelet clearance by macrophages in secondary dengue virus infections.

BACKGROUND: The mechanisms of thrombocytopenia and platelet phagocytosis in dengue illness are not fully understood. METHODS: A prospective hospital-based study was conducted to examine the relationships between platelet counts, serum thrombopoietin (TPO) levels, and platelet apoptosis and phagocytosis in 81 patients with secondary dengue virus (DV) infections and 38 healthy volunteers. The apoptosis and phagocytosis of cultured platelets after exposure to DV were also examined. RESULTS: Platelet apoptosis, platelet phagocytosis, and serum TPO levels were increased significantly in patients during the acute and early convalescence phases compared with levels observed in patients during the convalescence phase and in healthy volunteers. A significant correlation between platelet apoptosis and platelet phagocytosis was also observed in these patients. Platelet phagocytosis was inhibited significantly by the D89E mutant, which carries a point mutation in the RGD motif of milk fat globule-epidermal growth factor 8, a phosphatidylserine-recognizing bridge molecule. DV-induced platelet apoptosis and increased phagocytosis of DV-induced apoptotic platelets was confirmed using in vitro assays. CONCLUSIONS: Our data suggest an increased phagocytosis of DV-induced apoptotic platelets by macrophages via a phosphatidylserine-recognizing pathway in secondary DV infection. Accelerated platelet clearance, however, was overcome by TPO-induced enhanced thrombopoiesis in these patients. CLINICAL TRIALS REGISTRATION: UMIN000004835.

Outbreak of leptospirosis after flood, the Philippines, 2009.

After a typhoon in September 2009, an outbreak of leptospirosis occurred in Metro Manila, the Philippines; 471 patients were hospitalized and 51 (10.8%) died. A hospital-based investigation found risk factors associated with fatal infection to be older age, hemoptysis, anuria, jaundice, and delayed treatment with antimicrobial drugs.

Clinical and epidemiological features of human rabies cases in the Philippines: a review from 1987 to 2006.

BACKGROUND: Rabies viral infection causes a fatal encephalomyelitis. In humans, classic features include hydrophobia, aerophobia, hypersalivation, agitation, and neurological symptoms. In the Philippines, canine rabies contributes to a significant burden of human disease. METHODS: We retrospectively reviewed the medical records of 1839 patients admitted to San Lazaro Hospital, Manila, Philippines between 1987 and 2006, with a clinical diagnosis of rabies. We used the World Health Organization case definition for clinical rabies, which is defined by the presence of hydrophobia. RESULTS: Male patients outnumbered females by 2.2 to 1 and twice the number of adults were affected compared with children. Most patients were indigent. Dog bites occurred more than cat bites (97.1% vs. 2.9%) and most cases were caused by a single bite (86.2%), compared to multiple bites (8.7%). Bites to the face, head, and neck led to shorter incubation times, yet the incubation period varied, with most cases (42.7%) occurring in the bracket of 91-365 days post-exposure. Clinical symptoms included hydrophobia in all cases, as per our case definition, and aerophobia in 95.5%; only 9.4% had fever, 9.2% exhibited restlessness, and 6.7% exhibited hypersalivation. Localized neurological symptoms included pain (4.1%), numbness (2.6%), and itching (2.3%). None of the patients received appropriate post-exposure prophylaxis (PEP). CONCLUSIONS: This study examines the largest cohort of rabies patients reported to-date. Better understanding of clinical disease manifestations may help in salvage efforts to save patients with rabies. Knowledge of epidemiological factors will improve preventative efforts to reduce suffering from rabies.

Evaluation of a dengue IgG indirect enzyme-linked immunosorbent assay and a Japanese encephalitis IgG indirect enzyme-linked immunosorbent assay for diagnosis of secondary dengue virus infection.

To establish a new method for the diagnosis of dengue secondary infection, 187 serum samples from the patients with dengue secondary infection, 40 serum samples from the patients with dengue primary infection, and 44 serum samples from the healthy volunteers were tested using the dengue IgG indirect enzyme-linked immunosorbent assay (DEN IgG ELISA). The results of the test were compared with those from the dengue hemagglutination inhibition (DEN HI) test, which has been recommended as the gold standard by the World Health Organization (WHO, 1997). Japanese encephalitis IgG indirect ELISA (JE IgG ELISA) was also performed to measure anti-flavivirus IgG, which cross-reacts with the Japanese encephalitis virus, to test the possibility of an alternative to DEN IgG ELISA. The results of DEN IgG and JE IgG ELISAs were highly correlated with those of the DEN HI test. In the DEN IgG ELISA, a titer of 1:29,000 was the cut-off value for the diagnosis of dengue secondary infection (91.5% accuracy [95% confidence interval, CI], 90.9% sensitivity [95%CI], and 92.9% specificity [95%CI]). A titer of 1:52,000 was the cut-off value for dengue secondary infection using JE IgG ELISA (95.6% accuracy [95%CI], 98.9% sensitivity [95%CI], and 88.1% specificity [95%CI]). In conclusion, this study confirmed that the results of both DEN IgG and JE IgG ELISAs were highly correlated with the results of DEN HI test. Thus, these ELISAs are simple, rapid, sensitive, and quantitative tests that can be used in the determination of dengue secondary infection.

Increased phagocytosis of platelets from patients with secondary dengue virus infection by human macrophages.

The relationship between the percent phagocytosis of platelets by differentiated THP-1 cells was examined using flowcytometry and the peripheral platelet counts as well as platelet-associated IgG (PAIgG) in 36 patients with secondary dengue virus (DV) infections. The percent phagocytosis and the levels of PAIgG were significantly increased in these patients during the acute phase compared with the healthy volunteers. The increased percent phagocytosis and PAIgG found during the acute phase significantly decreased during the convalescent phase. An inverse correlation between platelet count and the percent phagocytosis (P = 0.011) and the levels of PAIgG (P = 0.041) was found among these patients during the acute phase. No correlation was found, however, between the percent phagocytosis and the levels of PAIgG. Our present data suggest that accelerated platelet phagocytosis occurs during the acute phase of secondary DV infections, and it is one of the mechanisms of thrombocytopenia in this disease.

Lack of efficacy of high-dose intravenous immunoglobulin treatment of severe thrombocytopenia in patients with secondary dengue virus infection.

Because most cases of secondary dengue virus infection are associated with an increased level of platelet-associated IgG, a high dose of intravenous immunoglobulin (IVIG) may have an effect on the development of severe thrombocytopenia in this disease. A randomized, controlled study was conducted with two treatment groups consisting of a treatment (IVIG) group (n = 15) and a non-treatment (non-IVIG) group (n = 16) to determine whether a high dose of IVIG is effective in hastening the recovery from thrombocytopenia in patients with secondary dengue virus infection. No significant difference was found in the baseline demographic data between the two groups. No adverse effect of IVIG was observed, but no effect in hastening the recovery of platelet counts was found in patients with secondary dengue infections. The lack of efficacy of IVIG suggests that platelet clearance by macrophages through Fc gamma receptors is not a primary mechanism in this disease.

Reducing the cost of post-exposure rabies prophylaxis: efficacy of 0.1 ml PCEC rabies vaccine administered intradermally using the Thai Red Cross post-exposure regimen in patients severely exposed to laboratory-confirmed rabid animals.

Purified chick embryo cell rabies vaccine (PCECV) administered as 0.1 ml intradermally according to the Thai Red Cross (TRC) regimen could reduce the cost of PEP by up to 84% when compared to the traditional five-dose Essen regimen. To confirm the efficacy of 0.1 ml of PCECV using the TRC regimen, a clinical trial was conducted in 113 patients presenting with category III exposures from confirmed rabid animals at two bite referral centres in the Philippines. Patients were monitored monthly for 1 year after exposure. PCECV was well tolerated, no vaccine-related serious adverse events occurred and all patients were alive 1 year after their initial exposure.

Correlation between increased platelet-associated IgG and thrombocytopenia in secondary dengue virus infections.

Although the public health impact of dengue is increasing rapidly, the mechanism of thrombocytopenia in this disease remains unknown. To elucidate this mechanism, the relationship between platelet-associated IgG (PAIgG) and platelet count in 53 patients in the acute phase of secondary dengue virus infection was investigated in a prospective-hospital-based study. A significant inverse correlation between the two parameters was found in these patients, while no correlation was observed in healthy volunteers. The low baseline platelet counts during the acute phase in 12 patients with secondary dengue virus infection significantly increased during the convalescent phase, while the increased PAIgG levels during the acute phase in these patients significantly decreased during the convalescent phase. Anti-platelet IgG autoantibody was detected rarely in the plasma of 53 patients with secondary dengue infection. The involvement of anti-dengue virus IgG was also shown in platelets from all of 8 patients in the acute phase of secondary dengue virus infection. These findings suggest that PAIgG formation involving anti-dengue virus IgG plays a pivotal role in the induction of transient thrombocytopenia during the acute phase of secondary dengue virus infection.