An outbreak of encephalitis affecting 265 patients (105 fatally) occurred during 1998-1999 in Malaysia and was linked to a new paramyxovirus, Nipah, that infected pigs, humans, dogs, and cats. Most patients were pig farmers. Clinically undetected Nipah infection was noted in 10 (6%) of 166 community-farm controls (persons from farms without reported encephalitis patients) and 20 (11%) of 178 case-farm controls (persons from farms with encephalitis patients). Case patients (persons with Nipah infection) were more likely than community-farm controls to report increased numbers of sick/dying pigs on the farm (59% vs. 24%, P=.001) and were more likely than case-farm controls to perform activities requiring direct contact with pigs (86% vs. 50%, P=.005). Only 8% of case patients reported no contact with pigs. The outbreak stopped after pigs in the affected areas were slaughtered and buried. Direct, close contact with pigs was the primary source of human Nipah infection, but other sources, such as infected dogs and cats, cannot be excluded.

Surveillance for Nipah virus (NV) was conducted in Thailand's bat population. Immunoglobulin G antibodies to NV were detected with enzyme immunoassay in 82 of 1,304 bats. NV RNA was found in bat saliva and urine. These data suggest the persistence of NV infection in Thai bats.

A retrospective serological and genetic study of hantaviruses responsible for hemorrhagic fever with renal syndrome (HFRS) in Greece during the last 17 years is presented. Fifty-one serum samples taken from 30 HFRS cases previously diagnosed by immunofluorescence assay were tested by ELISA for IgG (Hantaan, Dobrava, and Puumala) and IgM antibodies (Hantaan and Puumala). Results were compatible with the majority of infections being related to hantaviruses carried by rodents of the subfamily Murinae. RNA was extracted from 26 selected samples and reverse transcriptase-polymerase chain reaction (RT-PCR) was performed using primers specifically designed for the detection of hanta-viruses associated with murine (MS-N-specific, MM-G1-specific primers) or arvicoline rodents (PPT-N-specific primers). In addition, primers previously designed for the detection of the G2 coding region of the Murine-associated hanta-viruses were also used. Sequencing of the PCR products was then performed, followed by phylogenetic analysis of nucleotide sequence differences. Eleven out of the 26 serum samples tested were found to be positive by PCR with the MS-N primers, whereas four were positive with the MM-G1 primers, and only two with the G2 primers. None of the samples was found positive with the PPT primers. The sequence analysis showed that the virus that was responsible for these 11 HFRS cases was the Dobrava virus, which is endemic throughout the Balkans.

The 1999 outbreak of Nipah virus encephalitis in humans and pigs in Peninsular Malaysia ended with the evacuation of humans and culling of pigs in the epidemic area. Serologic screening showed that, in the absence of infected pigs, dogs were not a secondary reservoir for Nipah virus.

Nipah infection was not widespread among abattoir workers in Malaysia and was linked to exposure to pigs. Since it may be difficult to identify Nipah-infected pigs capable of transmitting virus by clinical symptoms, using personal protective equipment, conducting surveillance for Nipah infection on pig farms which supply abattoirs, and avoiding handling and processing of potentially infected pigs are presently the best strategies to prevent transmission of Nipah virus in abattoirs.