The past decade has seen the rise of many new diseases, and the re-emergence of others which were thought to have been brought under control. This is the combined result of the expansion of global trade and travel, the increase in populations of both humans and animals, and environmental changes.
Diseases in animals may affect human health in important ways. In some countries in Asia, rabies persists as a major public health problem. In Asia, Severe Acute Respiratory Syndrome is thought to have come from civet cats bred as exotic meat for Chinese markets.
Risk assessment strategies need to be developed, and effective surveillance and monitoring systems need to be in place. Emergency measures also have to be effective and well-organized. For this to be possible, there should be effective collaboration among different institutions in each country, and close international cooperation.
The World Health Organization has defined emerging infectious diseases as those which result from newly identified and previously unknown infections which cause public health problems, either locally or internationally. Some important emerging diseases of livestock and poultry in Asia are listed below.
Aujeszky's disease causes outbreaks of fatal nervous disease in suckling piglets. It was first reported in the Philippines in 1982, but when vaccines became widely available, reports of the disease declined. In 2002, 317 out of 4351 samples submitted for ELISA testing in the Philippines were confirmed as positive.
Avian Infectious Laryngotracheitis (ILT) is a disease of poultry caused by a herpes virus, and causes acute respiratory disease. In the Philippines, the first documented cases of ILT were in 1980.
Bovine spongiform encephalopathy (BSE) is a progressive, fatal, neurological disease of adult domestic cattle, probably caused by an abnormal protein known as a "prion". It was first diagnosed in Britain in 1986. In 1996, the occurrence of variant CJD (vCJD) in human beings was reported, and was thought to have a possible link with BSE. This news caused consternation all over the world. Until the occurrence of vCJD, no relationship had been observed between animal and human prion diseases. In Japan, as of September 2003, seven cases of BSE had been found. Today, BSE has become an important problem, not only for the animal industry, but also for public health.
Caprine arthritis/encephalitis is a viral infection of goats which may lead to chronic disease of the joints. It sometimes also causes encephalitis in kids less than six months old. The disease was introduced into the Philippines through the importation of 54 goats from Texas, USA in 1998.
Chronic wasting disease (CWD) is a similar to bovine spongiform encephalopathy, but is found in deer rather than cattle. CWD was first identified in the United States in the late 1960s in captive mule deer in a Colorado wildlife research facility, but it was not recognized as a spongiform encephalopathy until 1978. The known occurrence of CWD remained limited to captive mule deer until 1981, but within a decade was discovered in elk and other deer species. Infected elk were exported from Canada to Korea, representing the first known extension of CWD beyond North America.
Avian influenza is endemic among poultry all over the world, and is also found in wild birds. Sporadic outbreaks may occur of a highly contagious form of the disease, known as highly pathogenic avian influenza (HPAI). This is a systemic disease of poultry, with a high rate of mortality. It may sometimes be transmitted from infected poultry to human beings. HPAI is rarely isolated from wild birds and does not have a recognized wild bird reservoir.
Nipah virus is a highly contagious disease of pigs, characterized by a high fever and respiratory and nervous symptoms. It was first recognized in Malaysia in 1988. Nipah virus, a new paramyxovirus, is a threat to both human lives and the animal industry in Asian countries. The infection first started in Perak, in northern Malaysia, and spread rapidly to the south of the country. The disease spread to humans, especially those who had had direct contact with the infected pigs. Two hundred and sixty-five cases of viral encephalitis were recorded in humans, of whom 105 died. Other animals may be the source of the infection but the fact that the outbreak stopped after the culling of pigs suggested that infected pigs are required to sustain transmission.
Porcine proliferative enteropathy, caused by the bacteria Lawsonia intracellularis, is a disease of the gut which affects pigs. Young pigs are often affected by an acute form, while the disease may take a chronic form in older animals. Infected pigs are pale, suffer from diarrhea, and are reluctant to move. The presence of porcine proliferative enteropathy has been suspected in the Philippines, on the basis of clinical symptoms, but no cases have been confirmed. However, one study found that 41% of swine in seven commercial swine farms had antibodies to Lawsonia intracellularis. This suggests that they must have been exposed to the disease at some time in the past.
Porcine reproductive and respiratory syndrome (PRRS), caused by a virus, is characterized by the reproductive failure of sows, and respiratory problems in piglets and growing pigs. It was first described in 1987 in the United States, and appeared in Europe in 1990. Since then it has continued to spread. In 2001, five outbreaks of PRRS were confirmed by laboratory testing in the Philippines.
PMWS mainly affects pigs between 6 and 14 weeks of age. The syndrome tends to be slow and progressive, with a high fatality rate in affected pigs. A high proportion of cases of PMWS are associated with continuous production and the mixing of different sources of pigs.
Porcine Dermatitis and Nephropathy Syndrome (PDNS) is a serious concern worldwide, because the clinical signs and lesions closely resemble those of classical swine fever and African swine fever. PDNS was first reported in 1993 in Taiwan. PDNS generally occurs sporadically, with an incidence of less than 1% in affected herds. It mainly affects growers (about 40-70 kg, between 12 and 16 weeks of age).
A case of classical swine fever in a 700-sow farm reported in November 2002 in the Philippines turned out be a simultaneous outbreak of PMWS and PDNS. Herds with a combination of the two infections are also found in Taiwan, and in other parts of Asia.
Transmissible gastroenteritis is a common viral disease of the small intestine which causes vomiting and profuse diarrhea in pigs. Although the presence of transmissible gastroenteritis has been suspected earlier in the Philippines, only in July 2001 was an outbreak confirmed by diagnostic laboratory tests.
Emerging animal diseases appear to have a mixed impact on animal populations. Taiwan in 2002 had 13,054 pig farms producing more than 9.5 million pigs. The market head per sow was 15.4 in 1991 but this dropped to 13.5 in 2000. This decrease was partially attributed to the presence of PMWS and PDNS. In the Philippines, however, the population of cattle, water buffalo, goats, pigs, chickens and ducks has continued to increase, despite the emergence of new diseases.
Outbreaks of diseases often cause considerable losses of income. In 1997, an outbreak in the Philippines of strangles and influenza in racing horses killed at least 18 racehorses. Losses to the Philippine horse racing industry were more than US$ 9 million, as a result of cancelled race meetings, not to mention the cost of treating the animals. Outbreaks of Foot-and-Mouth (FMD) always result in heavy losses. If pigs are affected, many consumers stop eating pork. In countries where draft animals are used, their loss from FMD may result in crop losses because field work cannot be done. The presence of FMD and other diseases may also lead to a loss of export markets.
In addition to economic losses, the cost of quarantine during outbreaks and the cost of setting up and maintaining measures to prevent the entry of exotic diseases are considerable.
Various measures are being adopted by Asian countries to address the problem of emerging diseases and economically important animal diseases. These include the following:
With global free trade and new developments in animal health, Asian countries are passing new laws to prevent and control animal diseases. For example, several countries have passed laws forbidding the use of meat and bonemeal in livestock feed.
Rapid and accurate diagnosis of emerging diseases is of vital importance. Since emerging disease are, by their nature, unfamiliar to those working with livestock, special training and testing facilities are needed. Numerous training courses on the identification of emerging diseases are carried out each year in Asian and Pacific countries, attended by veterinarians, and sometimes by producers.
There are also on-going testing programs for several serious emergent diseases such as BSE. This disease is impossible to diagnose in living animals, and can be difficult to diagnose even in brain samples taken from dead ones. Testing for BSE is carried out in Korea and Thailand by immunohistochemistry (IHC). Additional tests can be done by Western Blot and ELISA (Platellia). A total of 5,907 bovine brain samples were tested for BSE in Korea from January 1996 to September 2003, but no evidence of BSE has been detected in any of the brain specimens submitted.
Both Thailand and Malaysia are carrying out a testing program for Nipah virus, particularly of pigs suffering from respiratory distress.
Emerging diseases need to be detected as quickly as possible, so that a control program can be put in place while the outbreak is still limited in extent. A surveillance network for this purpose has been established in Vietnam. As provided by the Veterinary Ordinance, the President of the Popular Committee of each Province is responsible for the animal diseases in his respective Province. This aims at providing an efficient network for gathering information.
In Taiwan, the Bureau of Animal and Plant Health Inspection and Quarantine (BAPHIQ) is working to establish standard procedures to deal with the eradication of infectious animal diseases. This includes strategies for eradication, decontamination procedures, management of exotic animal infectious diseases, and epidemiological investigation. Similar procedures are being developed in other parts of Asia.
Many emerging diseases in Asian countries are the result of importing infected live animals or animal products. Thus, regulation of imports, as well as strict border controls, are necessary to prevent the emergence of new diseases in animals.
Regulations governing the content of livestock feed is important in the control of BSE. Many Asian countries ban the use of mammalian meat and bone meal in livestock feed. Korea has developed a PCR test to detect meat and bone meal in feed (with a detection limit of 0.01%). Since March 2003, this test has been used by feedstuff inspection agencies.
Once an emerging disease has been detected, it is important to put in place an eradication program to try and prevent its spread. This usually involves eradicating all animals immediately on the infected farm(s), disposal of the carcasses, and thorough cleaning and disinfection of farm facilities. Generally the infected farm is isolated, and animal movement is restricted in a broad zone around the infected farm. There is monitoring of all animals which might be subject to the same infection, especially within the restricted zone.
Many diseases that have emerged in the countries of Asia have been introduced by imported animals. Because of the desire to improve the performance of local animals, many Asian countries import high-quality breeding stock, particularly from the United States, Europe and Australia. In addition, feed materials such as meat meal and bonemeal have also been imported. The practice in some Asian countries of using exotic animals for food or medicine has also contributed to the emergence of some diseases. Stricter controls are needed.
Accurate monitoring of diseases is still a problem in many Asian countries. This is because of a lack of trained personnel, inadequate laboratory facilities and insufficient funding. There is a need, therefore, to establish diagnostic laboratories and equip and train qualified staff to man these facilities. Some laboratories might provide diagnostic services on a national, or even a regional, scale.
Smuggling of animals and animal products is widespread in some countries in Asia. There is, therefore, a need for stricter control of the movement of animals, especially between countries that share a long border. Wide differences in livestock prices may encourage people on both sides of the border to trade, increasing the risk of animal diseases. In addition, screening facilities for diagnosis diseases are sometimes not available in quarantine at the port of entry. To reduce the possibilities of cross-border transmission of diseases, it is important to improve quarantine procedures and facilities.
In the global context, the emergence of new diseases usually necessitates the slaughtering of thousands, if not millions, of animals. However, in some countries, this measure is neither economically feasible nor politically acceptable. Instead of slaughtering, there is a need to develop effective vaccines, conduct research on immunology, develop anti-viral drugs and establish better methods of identifying carriers.
An important strategy in the fight against animal diseases is collaboration between different agencies, including government and non-governmental organizations and the general public. In addition, there is a need for more collaboration between Asian countries to address the problems of emerging diseases in Asia. This can be done through exchange of scientific information on these diseases, assistance in the diagnosis of diseases, training of personnel, and cooperation regarding transport of animals and animal products between countries.
Held at the Animal Health Research Institute, Tanshui, Taiwan ROC on November 10-15.
No. of countries participating: 9 (Canada, Indonesia, Japan, Korea, Malaysia, Philippines, Taiwan ROC, Thailand, Vietnam)
No. of papers presented: 13
No. of participants: 45
Co-sponsor: Animal Health Research Institute, COA
Figure 1 Piglet with Blisters around Muzzle from Foot and Mouth Disease (FMD)