Nearly 75% of all emerging infectious diseases (EIDs) that impact or threaten human health are zoonotic. The majority have spilled from wildlife reservoirs, either directly to humans or via domestic animals. The emergence of many can be attributed to predisposing factors such as global travel, trade, agricultural expansion, deforestation/habitat fragmentation, and urbanization; such factors increase the interface and/or the rate of contact between human, domestic animal, and wildlife populations, thereby creating increased opportunities for spillover events to occur. Infectious disease emergence can be regarded as primarily an ecological process. The epidemiological investigation of EIDs associated with wildlife requires a trans-disciplinary approach that includes an understanding of the ecology of the wildlife species, and an understanding of human behaviours that increase risk of exposure. Investigations of the emergence of Nipah virus in Malaysia in 1999 and severe acute respiratory syndrome (SARS) in China in 2003 provide useful case studies. The emergence of Nipah virus was associated with the increased size and density of commercial pig farms and their encroachment into forested areas. The movement of pigs for sale and slaughter in turn led to the rapid spread of infection to southern peninsular Malaysia, where the high-density, largely urban pig populations facilitated transmission to humans. Identifying the factors associated with the emergence of SARS in southern China requires an understanding of the ecology of infection both in the natural reservoir and in secondary market reservoir species. A necessary extension of understanding the ecology of the reservoir is an understanding of the trade, and of the social and cultural context of wildlife consumption. Emerging infectious diseases originating from wildlife populations will continue to threaten public health. Mitigating and managing the risk requires an appreciation of the connectedness between human, livestock and wildlife health, and of the factors and processes that disrupt the balance.
After examining the most recent scientific evidences, which assessed the role of some malaria plasmodia that have monkeys as natural reservoirs, the authors focus their attention on Plasmodium knowlesi. The infective foci attributable to this last Plasmodium species have been identified during the last decade in Malaysia, in particular in the states of Sarawak and Sabah (Malaysian Borneo), and in the Pahang region (peninsular Malaysia). The significant relevance of molecular biology assays (polymerase chain reaction, or PCR, performed with specific primers for P. knowlesi), is underlined, since the traditional microscopic examination does not offer distinguishing features, especially when the differential diagnosis with Plasmodium malariae is of concern. Furthermore, Plasmodium knowlesi disease may be responsible of fatal cases, since its clinical presentation and course is more severe compared with those caused by P. malariae, paralleling a more elevated parasitemia. The most effective mosquito vector is represented by Anopheles latens; this mosquito is a parasite of both humans and monkeys. Among primates, the natural hosts are Macaca fascicularis, M. nemestina, M. inus, and Saimiri scirea. When remarking the possible severe evolution of P. knowlesi malaria, we underline the importance of an early recognition and a timely management, especially in patients who have their first onset in Western Hospitals, after journeys in Southeast Asian countries, and eventually participated in trekking excursions in the tropical forest. When malaria-like signs and symptoms are present, a timely diagnosis and treatment become crucial. In the light of its emerging epidemiological features, P. knowlesi may be added to the reknown human malaria parasites, whith includes P. vivax, P. ovale, P. malariae, and P. falciparum, as the fifth potential ethiologic agent of human malaria. Over the next few years, it will be mandatory to support an adequate surveillance and epidemiological network. In parallel with epidemiological and health care policy studies, also an accurate appraisal of the clinical features of P. knowlesi-affected patients will be strongly needed, since some preliminary experiences seem to show an increased disease severity, associated with increased parasitemia, in parallel with the progressive increase of inter-human infectious passages of this emerging Plasmodium.
The genus Flaviviridae comprises about 70 members, of which about 30 are found in southern, south-eastern and eastern Asia and Australasia. These include major pathogens such as Japanese encephalitis (JE), West Nile (WN), Murray Valley encephalitis (MVE), tick-borne encephalitis, Kyasanur Forest disease virus, and the dengue viruses. Other members are known to be associated with mild febrile disease in humans, or with no known disease. In addition, novel flaviviruses continue to be discovered, as demonstrated recently by New Mapoon virus in Australia, Sitiawan virus in Malaysia, and ThCAr virus in Thailand. About 19 of these viruses are mosquito-borne, six are tick-borne, and four have no known vector and represent isolates from rodents or bats. Evidence from phylogenetic studies suggest that JE, MVE and Alfuy viruses probably emerged in the Malaya-Indonesian region from an African progenitor virus, possibly a virus related to Usutu virus. WN virus, however, is believed to have emerged in Africa, and then dispersed through avian migration. Evidence suggests that there are at least seven genetic lineages of WN virus, of which lineage 1b spread to Australasia as Kunjin virus, lineages 1a and 5 spread to India, and lineage 6 spread to Malaysia. Indeed, flaviviruses have a propensity to spread and emerge in new geographic areas, and they represent a potential source for new disease emergence. Many of the factors associated with disease emergence are present in the region, such as changes in land use and deforestation, increasing population movement, urbanization, and increasing trade. Furthermore, because of their ecology and dependence on climate, there is a strong likelihood that global warming may significantly increase the potential for disease emergence and/or spread.
Duck Tembusu virus (DTMUV), a newly emerging virus in ducks, was first reported in China in 2010. However, an unknown severe contagious disease associated with severe neurological signs and egg production losses in ducks, resembling to DTMUV infection, was observed in Thailand since 2007. To determine the presence of DTMUV in 2007, the clinical samples from affected ducks collected in 2007 were tested for DTMUV using pathological and virological analyses. Gross and histopathological lesions of affected ducks were mostly restricted to the ovary, brain and spinal cord, and correlated with the presence of flavivirus antigen in the brain and spinal cord samples. Subsequently, DTMUV was identified by RT-PCR and nucleotide sequencing of the polyprotein gene. Phylogenetic analysis of the polyprotein gene sequence revealed that the 2007 Thai DTMUV was a unique virus, belonged within DTMUV cluster 1, but distinctively separated from the Malaysian DTMUV, which was the most closely related DTMUV. It is interesting to note that the 2007 Thai DTMUV was genetically different from the currently circulating Thai and Chinese DTMUVs, which belonged to cluster 2. Our findings indicated that the 2007 Thai DTMUV emerged earlier from a common ancestor with the recently reported DTMUVs; however, it was genetically distinctive to any of the currently circulating DTMUVs. In conclusion, our data demonstrated the presence of DTMUV in the Thai ducks since 2007, prior to the first report of DTMUV in China in 2010. This study indicates that DTMUV may have circulated in the region long before 2010 and highlights high genetic diversity of DTMUVs in Asia.
In the interval 1994-1999, in Australia, Malaysia and Singapore, epizootic and epidemiological episodes of meningoencephalitis and severe acute respiratory syndromes were reported. Highly lethal in horses, swine and humans, the episodes were proved to be caused by the "new" viruses Hendra (HeV) and Nipah (NiV). At the same time three "new" viral agents have been isolated: Lyssavirus, Menanglevirus and Tupaia paramyxovirus. The intense contemporary circulation of people, animals and food products together with changes in human ecosystem favor new relations between humans and the "natural reservoirs" of biologic agents with a pathogenic potential for domestic and peridomestic animals and humans.
The Nipah virus was discovered twenty years ago, and there is considerable information available regarding the specificities surrounding this virus such as transmission, pathogenesis and genome. Belonging to the Henipavirus genus, this virus can cause fever, encephalitis and respiratory disorders. The first cases were reported in Malaysia and Singapore in 1998, when affected individuals presented with severe febrile encephalitis. Since then, much has been identified about this virus. These single-stranded RNA viruses gain entry into target cells via a process known as macropinocytosis. The viral genome is released into the cell cytoplasm via a cascade of processes that involves conformational changes in G and F proteins which allow for attachment of the viral membrane to the cell membrane. In addition to this, the natural reservoirs of this virus have been identified to be fruit bats from the genus Pteropus. Five of the 14 species of bats in Malaysia have been identified as carriers, and this virus affects horses, cats, dogs, pigs and humans. Various mechanisms of transmission have been proposed such as contamination of date palm saps by bat feces and saliva, nosocomial and human-to-human transmissions. Physical contact was identified as the strongest risk factor for developing an infection in the 2004 Faridpur outbreak. Geographically, the virus seems to favor the Indian sub-continent, Indonesia, Southeast Asia, Pakistan, southern China, northern Australia and the Philippines, as demonstrated by the multiple outbreaks in 2001, 2004, 2007, 2012 in Bangladesh, India and Pakistan as well as the initial outbreaks in Malaysia and Singapore. Multiple routes of the viremic spread in the human body have been identified such as the central nervous system (CNS) and respiratory system, while virus levels in the body remain low, detection in the cerebrospinal fluid is comparatively high. The virus follows an incubation period of 4 days to 2 weeks which is followed by the development of symptoms. The primary clinical signs include fever, headache, vomiting and dizziness, while the characteristic symptoms consist of segmental myoclonus, tachycardia, areflexia, hypotonia, abnormal pupillary reflexes and hypertension. The serum neutralization test (SNT) is the gold standard of diagnosis followed by ELISA if SNT cannot be carried out. On the other hand, treatment is supportive since there a lack of effective pharmacological therapy and only one equine vaccine is currently licensed for use. Prevention of outbreaks seems to be a more viable approach until specific therapeutic strategies are devised.
In addition to being a human pathogen, Staphylococcus aureus causes an array of infections in economically important livestock animals, particularly pigs. In Asia, there have been few reports on livestock-associated meticillin-resistant S. aureus (LA-MRSA), mostly from developed countries, with very few data available from resource-limited countries, not because of low prevalence but probably due to a shortage of diagnostic facilities. Unlike the wide spread of sequence type 398 (ST398) LA-MRSA in European countries and North America, ST9 predominates in most Asian countries. The prevalence of LA-MRSA among pigs in Asian countries varied widely (0.9-42.5%). The prevalence may vary by geographic location, age of pigs and sampling methodologies. Among pig farmers, the prevalence of nasal MRSA colonisation varied from 5.5% in Malaysia to 15% in China and 19.2% in Taiwan. Although most LA-MRSA isolates in Asia are of the same ST, molecular characteristics are not all the same. Dominant isolates in China were characterised as spa type t899-SCCmec III and t899-SCCmec IVb or V for isolates in Hong Kong, and t899-untypeable SCCmec for Taiwan. Dominant isolates in Malaysia were spa type t4358-SCCmec V and t337-SCCmec IX for isolates in Thailand. In addition, MRSA ST221 was reported in Japan and MRSA ST398 was isolated from commercial pigs in South Korea. Attention should be paid because pigs could become an important reservoir for MRSA and spread them to humans, as observed in many countries. There is a potential risk from the livestock reservoir to community and hospitals.
Since emergence of the Nipah virus (NiV) in 1998 from Malaysia, the NiV virus has reappeared on different occasions causing severe infections in human population associated with high rate of mortality. NiV has been placed along with Hendra virus in genus Henipavirus of family Paramyxoviridae. Fruit bats (Genus Pteropus) are known to be natural host and reservoir of NiV. During the outbreaks from Malaysia and Singapore, the roles of pigs as intermediate host were confirmed. The infection transmitted from bats to pigs and subsequently from pigs to humans. Severe encephalitis was reported in NiV infection often associated with neurological disorders. First NiV outbreak in India occurred in Siliguri district of West Bengal in 2001, where direct transmission of the NiV virus from bats-to-human and human-to-human was reported in contrast to the role of pigs in the Malaysian NiV outbreak. Regular NiV outbreaks have been reported from Bangladesh since 2001 to 2015. The latest outbreak of NiV has been recorded in May, 2018 from Kerala, India which resulted in the death of 17 individuals. Due to lack of vaccines and effective antivirals, Nipah encephalitis poses a great threat to public health. Routine surveillance studies in the infected areas can be useful in detecting early signs of infection and help in containment of these outbreaks.
Orf disease is known to be enzootic among small ruminants in Asia, Africa, and some other parts of the world. The disease caused by orf virus is highly contagious among small ruminant species. Unfortunately, it has been neglected for decades because of the general belief that it only causes a self-limiting disease. On the other hand, in the past it has been reported to cause huge cumulative financial losses in livestock farming. Orf disease is characterized by localized proliferative and persistent skin nodule lesions that can be classified into three forms: generalized, labial and mammary or genitals. It can manifest as benign or malignant types. The later type of orf can remain persistent, often fatal and usually causes a serious outbreak among small ruminant population. Morbidity and mortality rates of orf are higher especially in newly infected kids and lambs. Application of antibiotics together with antipyretic and/or analgesic is highly recommended as a supportive disease management strategy for prevention of subsequent secondary microbial invasion. The presence of various exotic orf virus strains of different origin has been reported in many countries mostly due to poorly controlled cross-border virus transmission. There have been several efforts to develop orf virus vaccines and it was with variable success. The use of conventional vaccines to control orf is a debatable topic due to the concern of short term immunity development. Following re-infection in previously vaccinated animals, it is uncommon to observe the farms involved to experience rapid virus spread and disease outbreak. Meanwhile, cases of zoonosis from infected animals to animal handler are not uncommon. Despite failures to contain the spread of orf virus by the use of conventional vaccines, vaccination of animals with live orf virus is still considered as one of the best choice. The review herein described pertinent issues with regard to the development and use of potential effective vaccines as a control measure against orf virus infection.