The Topic of This Month Vol.21 No.10(No.248)
Variety clinical symptoms caused by enteroviruses are currently known in this field. Poliovirus causes poliomyelitis accompanied with notorious sequela which paralyzes limbs. Since 1962, when live oral polio vaccine (OPV) was introduced, the National Epidemiological Surveillance of Vaccine-Preventable Diseases (NESVPD) has been established. From that period on, seroepidemiological survey for poliovirus-neutralizing antibody among healthy individuals (monitoring the people's immune status) and virus isolation from stool specimens of healthy children during the nonvaccination period (monitoring the circulation of poliovirus) have been made by prefectural and municipal public health institutes (PHIs). Surveillance for not only poliovirus but also other enteroviruses is being operated on a nationwide scale.
When the National Epidemiological Surveillance of Infectious Diseases (NESID) started in 1981, aseptic meningitis, hand, foot and mouth disease, and herpangina, representative enterovirus infections in children, were listed in the target diseases. Isolation of enteroviruses from these patients and their identification have been conducted as an activity of NESID by PHIs. These are now continued in compliance with the Law Concerning the Prevention of Infectious Diseases and Medical Care for Patients of Infections (the Infectious Diseases Control Law) enacted in April 1999. The results have been reported to and accumulated in the Infectious Disease Surveillance Center, the National Institute of Infectious Diseases. These reports tell that enteroviruses provoke epidemics of three target diseases and minor illnesses with or without exanthems showing main symptoms of fever and upper respiratory tract inflammation during summer in Japan, and that such epidemics may sometimes be detected in autumn or even later (see IASR, Vol. 17, No. 3; Vol. 19, No. 7; and Vol. 19, No. 8).
The reports of enterovirus isolation during 1982-1999 counted at 59,567, including 53 serotypes (Table 1) [Enteroviruses include poliovirus, group A coxsackieviruses (CA), group B coxsackieviruses (CB), echoviruses (E) and enterovirus (EV) 68 to 71]. E30, which caused nationwide epidemics three times during the period, was most frequently isolated, followed by CA16, E9, CB3, CB5 and CA4. Clinical specimens from which enteroviruses were isolated included mostly nasopharyngeal, stool and cerebrospinal fluid specimens. E30 was isolated mostly from cerebrospinal fluid; other serotypes mainly from nasopharyngeal specimens or stools. CA16 and EV71 were isolated from also vesicles.
Figure 1 shows enterovirus serotypes by the disease affecting the virus-yielding case. Enteroviruses were isolated from 18,581 meningitis, 6,857 hand, foot and mouth disease, and 8,289 herpangina patients. E30, CA16, and CA (CA4 and CA10) were mostly isolated from meningitis, hand, foot and mouth disease, and herpangina patients, respectively.
Reports of isolation of poliovirus have numbered at about 100 every year (3.1% of those of all enteroviruses) (Table 1). During this period, neonate to one-year-old accounted for 85%(1,551/1,825) of all poliovirus-yielding cases, most of which were vaccinees. Poliovirus isolation was also reported from those over the vaccination-recommended age (from 3 to 90 months, with a standard of 3 to 18 months) (see p. 214 and p. 217 of this issue). Of these isolates, vaccine-unrelated viruses were type 1 in a case in 1984 (a 7-year girl with encephalitis, from pharyngeal swab) and type 3 in another case in 1993 (a 13-year boy with upper respiratory tract inflammation, from pharyngeal swab) (see IASR, Vol. 18, No. 1). Neither was from paralytic cases and the origins of the two are unknown. All the other isolates were considered to be vaccine-related virus.
Toward polio eradication, more vaccination and surveillance for acute flaccid paralysis (AFP) patients are being lead by World Health Organization (WHO) from 1988. Since wild poliovirus has not been isolated from paralytic cases in Japan after 1980, it has been taken for granted that poliomyelitis due to wild-type virus has already been controlled. However, to confirm the fulfillment of the criteria of WHO for certification of polio eradication, AFP surveillance has been intensified since 1997 (see IASR, Vol. 19, No. 5). This surveillance has reconfirmed that poliomyelitis has not been overlooked (see p. 214 of this issue). The enterovirus surveillance carried on for decades seems to be highly significant as the background. The Western Pacific Regional Office (WPRO) of WHO is about to declare polio eradication in October 2000 (see p. 214 of this issue).
Virus isolation in 2000: Of the reports of enterovirus isolation as of September 25, EV71 has most frequently been isolated (Table 1). Both EV71 and CA16 have been isolated from hand, foot and mouth disease cases; reports of EV71 isolation have been increasing (EV71 isolation was more often in 1997, while that of CA16 more often in 1998-1999). EV71 isolation from patients accompanying meningitis is also increasing (see IASR, Vol. 21, Nos. 4-8 and p. 220 of this issue and http://idsc.nih.go.jp/iasr/index.html). EV71 isolation from severe cases accompanying encephalitis or myocarditis have sometimes been reported. Such frequent occurrences of fatal cases among children as those seen in Malaysia in 1997 and Taiwan in 1998 (see IASR, Vol. 19, No. 7) have not been encountered in Japan, nevertheless, further monitoring is indispensable.