Assessing potential countermeasures against the dengue epidemic in non-tropical urban cities.

BACKGROUND: Dengue is a common mosquito-borne viral disease epidemic especially in tropical and sub-tropical regions where water sanitation is not substantially controlled. However, dengue epidemics sometimes occur in non-tropical urban cities with substantial water sanitary control. Using a mathematical model, we investigate what conditions can be important for a dengue epidemic to occur in an urban city such as Tokyo, where vectors are active only in summer and there are little number of vectors around hosts. METHODS: The model, which is a modified Ross-Macdonald model, consists of two sets of host-vector compartments. The two sets correspond to high-risk and low-risk areas, and only hosts can move between them. Assuming that mosquitoes have constant activity for only 90 days, we assess five potential countermeasures: (1) restricted movement between the two areas, (2) insecticide application, (3) use of repellents, (4) vector control, and (5) isolation of the infected. RESULTS: The basic reproduction number R 0 and the cumulative number of infected hosts for 90 days are evaluated for each of the five countermeasures. In the cases of Measures 2-5, the cumulative number of the infected for 90 days can be reduced substantially for small R 0 even if R 0>1. Although R 0 for Measure 1 monotonically decreases with the mobility rates, the cumulative number of the infected for 90 days has a maximum at a moderate mobility rate. If the mobility rate is sufficiently small, the restricted movement effectively increases the number density of vectors in the high-risk area, and the epidemic starts earlier in the high-risk area than in the low-risk one, while the growth of infections is slow. CONCLUSIONS: Measures 2-5 are more or less effective. However, Measure 1 can have the opposite effect, depending on the mobility rates. The restricted movement results in the formation of a kind of core population, which can promote the epidemic in the entire population.

Prevalence of hepatitis E virus (HEV) infection in wild boars (Sus scrofa leucomystax) and pigs in Gunma Prefecture, Japan.

The prevalence of hepatitis E virus (HEV) infection in wild boars and pigs in Gunma Prefecture, Japan, was serologically and genetically examined. The positive detection rates of anti-HEV IgG and HEV RNA in the wild boars were 4.5% (4/89) and 1.1% (1/89), whereas those in the pigs were 74.6% (126/169) and 1.8% (3/169), respectively. The positive rates of anti-HEV IgG and HEV RNA on the 17 pig farms in the present study ranged from 20% to 100%, respectively. One male wild boar approximately 5 years of age was positive for HEV RNA but was negative for anti-HEV IgG. Three pigs from 2 farms were positive for HEV RNA; 2 of these pigs were negative for HEV IgG, and the other was positive. A phylogenetic analysis revealed that all of the HEV ORF1 genes detected in the present study belonged to genotype III. In Gunma Prefecture, HEV is highly prevalent and widespread, and uncooked wild boar and pig meat may have the potential to transmit HEV to humans.

Sequence and phylogenetic analysis of the nucleoprotein (N) gene in measles viruses prevalent in Gunma, Japan, in 2007.

In 2007, relatively large outbreaks of measles occurred in the Kanto region of Japan, including Gunma Prefecture. We performed sequence and phylogenetic analysis of the nucleoprotein gene (N gene) of measles viruses from 3 measles patients in this area in May 2007. The N gene sequences of the present strains were identical to each other, and phylogenetic analysis showed these viruses were classified into genotype D5. The results suggest that highly homologous measles viruses may be associated with outbreaks of measles in Gunma, Japan.