M. Sugamata ( Department of Hygiene, Tegine, Teikyo University School of Medicine, Tokyo, Japan. )
R. Khono ( Department of Bacteriology, Saitama Medical College, Saitama, Japan. )
Akhtar Ahmed ( Department of Neurology, Dow Medical College, Civil Hospital, Karachi, Pakistan. )
T. Takasu ( Department of Neurology, Nihon University School of Medicine, Tokyo, Japan. )
Seroepidemiological investigations were done during the study of viral encephalitis in and around Karachi, Pakistan. Serum and /or cerebrospinaF fluid (CSF) from 352 persons (72 patients with encephalitis, 199 patients without neurological disease and 81 healthy volunteers) were collected during the period from June, 1983 to March, 1984. Of 72 encephalitis patients, serum antibody positivity rates were over 45 percent against Herpes simplex type I virus (HSV), measles and rubella virus, and less than 33 percent against entero-70 virus consistently through the investigation period. In contrast, the antibody positivity rate against Japanese encephalitis (JE) virus increased from pre-rainy to post-rainy seasons in both encephalitis patients and controls. Positive antibody in CSF was detected in nine cases against HSV, in five cases each against measles and JE virus, and in four cases against rubella. (JPMA36:177, 1986).
Many cases of subacute scierosing pan encephalitis (SSPE) have been clinically recognized in Karachi1. In addition it has been clinically observed by the same author (A.A) that many kinds of encephalitides occur in Karachi. However, virological diagnosis of the encephalitides occurring in Karachi has not yet been explored systematically. Therefore, virological and seroepidemiological investigations were undertaken as part of a multidisciplinary research Project to identify the causative agents and to clarify the status of the occurrence of encephalitides in Karachi area.
This report, summarizes the results of seroepidemiological investigations in Karachi.
MATERIALS AND METhODS
SUBJECTS. Groups of subjects are summarized in Table I.
SAMPLES; Sera were collected from all the individuals of each group and Cerebrospinal fluid (CSF) samples only from patients with encephalitis at Department of Neurology, Dow Medical College and Civil Hospital, Karachi. SAMPLING PERIOD. All the samples pertaining to this report were collected from the beginning of June, 1983 to the middle of March, 1984.
Test methods for detecting viral antibody are shown in Table II.
Infection with west nile virus (WNV) has been reported both in men and animals in Punjab2. In general WNV does not cause encephalitis, but a large part of the antigen structure of the virus is common to that of JEY, tickborne encephalitis virus (TBEV) or Dengue virus (DV) therefore antibody titers against TBEV, against WNV, against 1TW were also measured: Animals breeding around Karachi were also for viral (JEV, WNV, D-2) antibodies the months of August and September,tested during1983.
1. ANTIBODY POSITIVITY RATE:
(A) Encephalitis Patients; a) Serum: The seasonal transition of antibody positivity rate seems to be divided into two types (Table III).
One type covers JEV, TBEV, WNV and DV, the rates against them being subject to the seasonal variation. In contrast, in the other, the rates are consistently high (MV, RV and HSV), or low (EV-70) through the entire sampling period. b) CSF: CSF was available in 42 encephalitis patients. Cases with positive antibody titers are shown in Table IV.
The highest positivity rate was observed against HSV. None of the cases showed positive antibodies against TBEV or EV-70.
(B) Persons without encephalitis:
a) Serum antibody against arboviruses: Serum antibody positivity rate in patients without neurological disease and healthy volunteers are shown in Table V.
Increase of antibody positivity rate after rainy season was observed, and this trend was similar to that observed in the patients with encephalitis.
II. ANTIBODY TITER AGAINST ABROVIRUSES:
In all three groups of subjects, serum antibody titers against arboviruses were elevated from July to September. The titers in patients without neurological disease taken as a representative sample are shown in Figure 1.
Reciprocal cross reactions were recognized between JEV, WNV, TBEV and EN. The proportion of cases showing JEV antibody titer over 23 times higher than that of WNV antibody titer was three percent (five cases), and that of DV antibodywas 13 percent (21 cases).
The results of this serological investigations indicate that (Table VI)
1EV, HSV, MV, RV and EV-70 may be the causative agents of the encephalitides occurring in and around Karachi. JAPANESE ENCEPHALITIS: The cases with serological evidence of JEV infection are shown in Table VII. The evidence includes an increase of serum antibody titer in paired samples, or a high titer of serum and CSF positive antibody. All of these cases considered to be JE were observed during the period from September, 1983 to March, 1984.
HERPES ENCEPHALITIS: In 40 encephalitis patients only IgG antibody against HSV was detected while in one case antibodies against both JEV and HSV were found.
MEASLES ENCEPHALITIS. To date, an appreciable incidence of SSPE in Karachi was suggested by Ahmed in 19801, but only based on clinical features. In 1982, Takasu found a case of SSPE with clinical and serological evidence during the preparatory investigation of this Project. In the present study, five cases showed positive CSF antibody against M,V and one of the five cases showed a high titer.
ENCEPHALITIS CAUSED BY TBEV, RV AND EV70: of encephalitis patients, none were considered to be due to TBEV, RV or EV-70.
This work, is ‘being done in collaboration with the staff of Neurology Department especially Miss Shagufta Shaikh, under the generous approval and great help by the Principal of DMC, the Medical Superintendent and staff of Central Laboratory of Civil Hospital,’ Karachi. The authors express their deepest gratitude to them all.
The authors wish to thank Professor Teiji Miura, Department of Hygiene, Teikyo University School of Medicine, for his advice and critical reading for the manuscript.
This study was supported by a grant-in-aid for Overseas Scientific Survey, Ministry of Education, Science and Culture, Japan (1983, No. 58041070).
1. Abmed, A. Sub-acute scierosing pan encephalitis. A report of seven cases. JPMA., 1980; 30:249.
2. Hayes, C. G., Baqar, S., Ahmed, T., Chowdhry, M.A. and Reisen, W.K. West Nile virus in Pakistan. 1. Sero-epidemiological studies in Punjab Province. Trans. R. Soc. Trop. Med. Hyg., 1982; 76:431.