Dengue fever is a mosquito-borne viral disease. Dengue virus (DENV) infections occur in most of the tropical and subtropical areas of the world. DENV infection with any of four serotypes leads to a broad spectrum of clinical symptoms and their severity, including asymptomatic infection, dengue fever (DF) and fatal dengue hemorrhagic fever (DHF). DF/DHF is considered to be one of the most important re-emerging infectious diseases. Physicians and pediatricians in non-endemic countries are often unfamiliar with the symptoms and unaware of the potential importation of patients with DF/DHF. In August of 1942, an epidemic occurred suddenly in Nagasaki city and then in Sasebo city, Osaka and Kobe city. The epidemic in 1942 was subsided in November, but in the next summer it broke out again and recurred every summer until 1945. There were no dengue endemics in Japan since then. In late August of 2014, three autochthonous dengue cases were reported in Japan. Since then, as of 31 December 2014, a total of 162 autochthonous cases have been confirmed. While cases were reported from throughout Japan, the majority was linked to visiting a large park or its vicinity in Tokyo, and the serotype detected has been serotype 1.
The mosquito transmits various illness to the human. The major transmitter mosquito is the genus Anopheles, the genus Culex and the genus Aedes. There are some differences in the site of larva’s occurrence, the blood-sucking behavioral pattern, the blood-sucking preference and the winter style, between genera. It is important for Disease Control and Prevention to understand taxonomy and ecology of mosquitoes. To investigate the rate of mosquitoes keeping Japanese encephalitis virus, we collected mosquitoes at pig farms by CO2 net traps in Kumamoto from 2012 to 2013. Approximately 20,000 out of about 23,000 captured mosquitoes have been identified as Culex tritaeniorhynchus (Ct). Twenty eight out of 520 pooled mosquito were Japanese encephalitis virus (JEV) gene positive by PCR assay. Genotype I of JEV was isolated from the 2 pooled samples. At the result of phylogenetic tree analysis of isolates, the strain that was isolated from mosquitoes in 2012 was correlated with the cluster that have been isolated from mosquitoes at Korea in 2010. The homology of these strains was 99% at envelop (E) gene region. In addition, the E region of the strain from mosquitoes in Korea in 2010 completely corresponded to that of the isolates from pigs at Kumamoto in 2009 and 2010. Additionally, to investigate whether the Ct has come from the continent, eight Ct were collected by net traps for planthoppers. Two Ct were determined to be the continent genotype by analysis of the mosquito mitochondrial DNA (COI), but JEV gene was not detected from these Ct. Results of the phylogenetic tree analysis of these JEV isolates and the analysis of COI, suggested the possibility that the Ct keeping JEV has come from the continent.
In Japan, infectious diseases including mosquito-borne diseases are controlled based on the Infectious Disease Control Act (April 1999) which allows public health authorities to take various control measures against the designated infectious diseases. These measures include mandatory notification by physicians, active surveillance of cases and vector-control program etc. Under the Infectious Diseases Control Act, approximately 10 mosquito-borne diseases are designated; such as malaria, dengue fever, chikungunya fever. Every year, a number of imported cases of these mosquito-borne diseases have been reported. However, as auto-chthonous cases, we only have less than 10 cases of Japanese encephalitis annually in these years due to the effective implementation of vaccination. Meanwhile, at the end of August 2014, an autochthonous case of dengue fever was confirmed for the first time in the past 70 years. The patient never travelled abroad, and was considered to be infected with dengue virus in Yoyogi Park located in the center of Tokyo based on the activity history and other evidence. This was followed by the report of approximately 160 autochthonous cases by the end of October, and most of the patients had visited Yoyogi Park or its adjacent areas. Through the response to this dengue outbreak in 2014, it was revealed that the knowledge and experience in mosquito control had been weakened or even lost among Japanese public health authorities. To solve this problem and to promote mosquito-control measures, in April 2015, Ministry of Health, Labour & Welfare announced the “Special Guidance on Mosquito-borne Diseases” which identifies the roles to be played by each stakeholder including the Government, prefectural and municipal governments, physicians/medical institutes and the general public. It is expected that mosquito-borne disease control will be further enhanced by active promotion of this Guidance.
2) Supplements of 43rd Congress of Veterinary Epidemiology
We developed a deterministic mathematical model to grasp transmission features of the large scale epidemic of Ebola virus disease (EVD) occurred in the West African region since March 2014. Basic reproduction number (R0) was estimated as 1.32, and the number of days between clinical onset and isolation into caretaking facilities was estimated as 5.0 days. If the days to isolation was less than 3.3 days, the epidemic was considered to be successfully controlled.
This is the report of strategic surveillance seminar held in Tokyo University on November 5th, as 42nd scientific seminar of the Japan Society of Veterinary Epidemiology. Two lectures are included here; “Basis and Practice of Surveillance in Animal Health” by Dr. Sota Kobayashi (NIAH), and “Policy and economic constraints on developing efficient surveillance strategies” by Dr Katharina D.C. Stärk (RVC). Dr Kobayashi introduced the basis of surveillance and its practice in Japan. Dr Stärk explained the policy constraints and economic constraints of surveillance in animal and public health.