The Sunday Mail
Dr Unesu Ushewokunze-Obatolu
High impact animal diseases are the main reason for the existence of a national veterinary service. Their occurrence being often sudden, they typically tend to spread fast and lead to heavy production losses, thereby defeating the aims of food and nutritional security, agricultural and economic development as well as threatening livelihoods.
Over the last 10 or so years, Avian influenza has been occurring in different parts of the world, particularly in Europe and on the Asian sub-continent or the far East, decimating poultry flocks and disrupting commerce involving poultry and poultry products.
Lately, outbreaks of highly pathogenic avian influenza (HPAI) have been reported on all continents, Africa included. Different sub-types and strains are more relevant to particular geographical areas. In Africa, the disease has occurred in Burkina Faso, Cameroon, Côte d’Ivoire, Ghana, Niger, Nigeria and Togo for H5N1 and in Nigeria, Egypt and recently Uganda, affecting viability of poultry keepers in the vicinities of Lake Victoria.
In all these countries, no human cases were recorded. Avian influenza, as the name implies, is a group of infectious conditions occurring naturally in wild water birds (ducks, geese), in which they are usually harboured without affecting their hosts.
The causative agent is a virus belonging to the Influenza type A group. The virus occurs as variants with different levels of infectivity and clinical expression, some being more benign than others. The various types are also continually recombining and re-assorting in nature to form new types with new characteristics.
When certain types of the virus cross into domesticated birds especially chickens, turkeys and pet birds, they may result in severe illness and rapid progression to death. Some forms take on a character to cause human disease. It is the highly pathogenic strains, which are of interest to public health either being decimative to poultry or by being both poultry and human pathogens.
Although there are rare examples of others, the highly virulent HPAI viruses found in nature have usually been the H5 or H7 types. Around 2006, a highly pathogenic AI virus strain referred to as H5N1 of Asian origin attracted much attention because of significant outbreaks that occurred in different parts of the world in domestic and wild birds.
Concern was raised on the severity of the disease not only in poultry but also in wild birds as well as its ability to infect mammalian species. Avian influenza is a notifiable disease in Zimbabwe and is also listed by the World Organisation for Animal Health (OIE) among diseases of global importance. All countries are obliged to report occurrence of sub-types H5 and H7 of the Avian influenza virus within their territory to the OIE.
Highly pathogenic viruses can cause severe clinical signs and up to 90-100 percent mortality in birds, epidemics may spread rapidly, devastating the poultry industry and resulting in severe trade restrictions.
The lowly pathogenic viruses cause little or no clinical signs in birds. Effectively, all birds are considered to be at risk of infection and occasionally mammals includinghumans are infected due to close contact with infected poultry. The viruses can survive in the environment at low temperatures for up to several months, but are susceptible to a variety of disinfectants.
Avian influenza viruses can be spread through a variety of ways, including but not limited to:
- Direct contact with secretions and excretions from infected birds, especially faecal matter manure or feathers, or through contaminated feed, water, equipment and clothing;
- International trade of poultry and poultry products, legally and illegally;
- Marketing practices, especially at live bird markets;
- Farming practices where infected materials are moved from one farm to another; and
- Movement of infected wild birds.
Wild birds have been demonstrated to be natural reservoirs of AI viruses, harbouring the virus in their bodies without showing any clinical signs.
There is no specific treatment for the disease.
Good hygiene and husbandry practices, including good nutrition and general biosecurity, can guarantee freedom from infection.
Poultry premises should foster continuous separation from contact with wild birds, which may harbour infection.
Some specific measures recommended at farm level include:
- Keeping poultry safe distances away from areas frequented by wild fowl;
- Maintaining good control on access to poultry houses by people and equipment;
- Eliminating elements such as trees on property that may attract wild birds;
- Maintaining good sanitation of property, poultry houses and equipment;
- Avoiding the introduction of birds of unknown disease status into flock;
- Quickly reporting illness and death of birds to veterinary authorities; and
- Appropriate disposal of manure and dead poultry.
Rapid response is vital for containing avian influenza outbreaks. Eradication by slaughter of infected flock is usual the preferred option where the disease is still limited to specific locations in chickens and turkeys. In outbreaks, a regime of slaughter, correct disposal of carcasses, cleaning, disinfection, isolation, 21-day intervals to re-stocking should be followed.
Survivors can be expected to have a high degree of immunity but may harbour virulent virus.
Due to the potential for human infection with some strains of the virus, it is recommended that people working with, or in contact with poultry suspected of being infected with AI, wear protective clothing including facemasks, goggles, gloves and boots.
Vaccine technologies are available for emergency, control and prevention of HPAI. However, their use may, in some cases, complicate the ability to detect behaviour of the disease.
Decisions to use vaccines are determined by prevailing circumstances of risk. It is widely believed that migratory birds, which move in line with seasons from the northern to the southern hemispheres and vice-versa annually, carry the virus from hotspots to other areas.
Migratory birds follow set flyways and are thought to pass the infections to resident water birds, which, in turn, pass the viruses to domestic and other local birds, precipitating infection and disease.
Presence of water bodies frequented by wild birds is, therefore, a risk factor for the spread of Avian influenza to domestic fowls. Zimbabwe has no less than 10 000 water bodies and with the good rains received in the last season, the risk of Avian influenza may have risen.
Poultry production has been the fastest-growing livestock sub-sector with intensive commercial, numerous backyard and free-range flocks all over the country. Every household and commercial producer, therefore, needs to be on the lookout for unusual illness and deaths and enlist veterinary advice.The important thing is to avoid moving sick birds as this would be one way to spread diseases to other areas.
Dr Unesu Ushewokunze-Obatolu is the Principal Director of the Livestock and Veterinary Services Department. She wrote this article for The Sunday Mail
