Akhtar Ahmed

Detection of West Nile and Japanese Encephalitis Viral Genome Sequences in Cerebrospinal Fluid from Acute Encephalitis Cases in Karachi, Pakistan

Reverse transcriptase‐polymerase chain reaction (RT‐PCR) on 24 cerebrospinal fluid (CSF) specimens collected between February and August 1992 detected genome sequence of West Nile (WN) virus in 8 specimens and Japanese encephalitis (JE) virus in a single specimen. The results, combined with the data by IgM‐ELISA on CSF indicated that a significant proportion of acute encephalitis cases in Karachi, Pakistan, were caused by WN virus infection, while JE virus caused a small fraction.

Neurological Diseases in Karachi, Pakistan – Elevated Occurrence of Subacute Sclerosing Panencephalitis

Neurological diseases, especially subacute sclerosing panencephalitis (SSPE), were surveyed in Karachi, Pakistan disclosing following major results. (1) Indirectly estimated prevalence rates of selected neurological disease entities were comparable with the rates from western countries and Japan in heredodegenerative diseases, but grossly elevated in infectious diseases. (2) Estimated mortality statistics for the Karachi community revealed highly elevated rates for infectious, parasitic and perinatal causes of death. (3) SSPE represented about 10% of inflammatory afflictions of the cerebral parenchyma, its incidence rate being about 100% times more than that observed in developed countries. A case-control study preliminarily showed that infants who later contract SSPE have unhealthy mothers, are born small, and have various occurrences of ill health from birth to the onset of SSPE. (4) Age at the onset of measles was very young in the cases as well as in controls, unlike the average young age at onset of cases only in developed countries. Measles contracted at young age is a well known risk factor to SSPE. Whereas few children in developed countries acquire measles at such an early age, many Karachi children do. Elevated occurrence of SSPE is probably conditioned by such age patterns of measles infection, together with other risk factors more common in Karachi due to poorer health standards. A proper immunization programme is urgently needed to control measles and SSPE.

Structural homology between hemagglutinin (HA) of measles virus and the active site of long neurotoxins

The amino acid sequence of a carboxy terminal domain corresponding to the end of the outer envelope projection of the hemagglutinin glycoprotein (HA) of measles and subacute sclerosing panencephalitis viruses has a high degree of homology with the active domain of long neurotoxins, which specifically binds to the nicotinic acetylcholine receptor. The homology in amino acid sequence of HA to this domain of neurotoxin, as well as native alpha-bungarotoxin (BTx), was confirmed by the following evidence: a) rabbit anti-HA monospecific sear reacted with BTx in ELISA, b) HA dose-dependently blocked the binding of radio-labeled BTx in competitive radioimmunoassay, and c) antibody to a synthetic peptide of the active domain of BTx precipitated HA in radioimmunoprecipitation. In addition, SSPE patients had significantly high titers of antibody to BTx than healthy children who had been previously infected with measles. This epitope of HA may play an important role in the transsynaptic spreading of the virus in the brain.

Virological and serological studies on poliomyelitis in Karachi, Pakistan. I. Outbreaks in 1990-91.

Between October 1989 and September 1991, 124 cases of poliomyelitis visited the Department of Paediatrics, Civil Hospital Karachi, Pakistan. The majority of them were between 6 months and 2 years of age and the epidemics occurred during the hot seasons. The dominant serotype was poliovirus type 1 during the epidemic season in 1990 and type 2 in 1991. All the polioviruses isolated from the patients were wild‐type. Virological studies also disclosed that enteroviruses other than polioviruses were prevalent among healthy children as well as among diarrheal and polio patients.

Elevated ratio of late measles among subacute sclerosing panencephalitis patients in Karachi, Pakistan.

Subacute sclerosing panencephalitis (SSPE) in Western countries and Japan is found more often in early- than in late-measles sufferers. Recent SSPE findings in Karachi, however, present a different picture. Age at measles contraction was obtained and analyzed for 44 SSPE patients identified in Karachi between 1983 and 1988. The ratios of early- (< 2 years of age) and late- (> or = 2 years of age) measles sufferers among 36 of these patients who had experienced only one attack of measles were 0.33 and 0.67, respectively. This is in striking contrast to the predominance of early measles in the SSPE histories reported in Japan and an number of Western countries.

Epidemiology of poliomyelitis in Karachi, Pakistan: Prospective studies during 1990–93

Between October 1989 and September 1993, 245 cases of poliomyelitis visited the Department of Pediatrics, Civil Hospital Karachi, Pakistan. The majority of them were between 6 months and 2 years of age and the epidemic occurred during the hot season. The dominant serotype was polio type 1. All of the polioviruses isolated from the patients were wild type. Virological studies also disclosed that enteroviruses other than polioviruses were prevalent among healthy children as well as diarrheal and polio patients. Serodiagnosis by poliovirus‐specific immunoglobulin M antibody tests using the capture enzyme‐linked immunosorbent assay method were in good agreement with the results of virus isolation. The present study demonstrated that Pakistan is a region endemic for wild poliovirus and more aggressive preventive measures are needed to eradicate poliomyelitis from the region.