ANTIBIOTICS ARE generally not effective against viruses simply because they do not have their own metabolic mechanism and that viruses are usually intra cellular organism because they have to utilize the machinery of host cell for their proliferation. Very few chemicals are effective against viruses as virucidal. The most important to mention here two groups:
1. Amantadine and Remantadine.
2. Oseltamivir and Zenamiver.
The first group prevent the assembly of virion in host cell and the second group acts by preventing the virus to go out of the host cell.
History of resistance: Amantadine has long been known for its effectiveness against Influenza viruses also against Herpes simplex and Herpes zoster in human. Soon after the first incidence of H5N1 (Bird flu) fatal infection in human in Hong Kong in 1997, it was realized that H5N1 viruses are resistance to Amantadine drug.
It has been reported internationally, although not accepted officially, that resistance against Amantadine was brought about in avian influenza viruses through indiscriminate use of this drug by Chinese poultry farmers to curb avian influenza during late 1990′s.
It has been reported that Amantadine manufactured by Chinese companies was available to the local farmers at 10 Dollars for a pound of the drug. The drug has been used for treatment as well as prevention of avian influenza viruses. This means that prior to the development of resistance reported during 1997, the drug had been in use for years in poultry production in China.
A group of researchers in USA reported during 2005 the diversity of amantadine-resistant mutants among avian influenza A viruses with pandemic potential (H5, H6, H7, and H9 hemagglutinin subtypes). Drug-resistant variants were not detected among 1979–83 isolates, whereas 31.1% of H5 and 10.6% of H9 strains from Southeast Asia isolated in 2000–04 carried mutations in M2 protein. In North America, resistant variants occurred among H7 viruses only 16.4% of those tested. H6 viruses were amantadine-sensitive. These findings prompt concern regarding the control of pandemic influenza, the possibility that the next pandemic virus will be amantadine-resistant and the need to monitor the use of the drug in poultry.
Situation in Pakistan: The commercial poultry producers in Pakistan were not acquainted of the use of Amantadine for control of avian influenza viruses in poultry before 2007. During 2007 the first such drug came into market in combination with Flouroquinalone. Unfortunately this introduction of Amantadine in the country was not opposed by the concerned quarters specially the Pakistan Poultry Association. Although the highly pathogenic avian influenza (HPAI) viruses (H5N1) in poultry was brought under control since 2008 through the efforts under National Program for Control and Prevention of Avian Influenza (NPCPAI), the use of Amantadine in commercial poultry grew with the time because of wide spread of H9 in commercial poultry flocks. soon after the first registration of antiviral, a flood of commercial medicinal products containing Amantadine in combination with antibiotics came in market and use of this product is at its peak in poultry production in Pakistan.
Three types of avian influenza viruses namely H5, H7 and H9 are known to be prevalent in Pakistan. The highly pathogenic avian influenza H7 type was first reported in Pakistan during 1994 but the disease was controlled through good biosecurity and vaccination. The same was the case with H5 when the virus attacked the commercial poultry during 2006. Although both the high path viruses mentioned above are no more active in the country but at the same time milder strain H9 subtype is widely prevalent across the country not only in commercial poultry but also in rural chicken and other wild and fancy birds like Pheasants. As a result of increased use of Amantadine, this virus type (H9) is more likely to develop resistance against this drug which may lead to a disaster in human if virus mutates into an highly pathogenic form in future in the country.
What needs to be done: It is high time to review the use of this antiviral drug (Amantadine) in commercial poultry in the country so as to analyze the merits and demerits of the use of this antiviral drug in poultry. Decisions are needed to be taken on both public and private offices and implemented with a sense of responsibility.
Information, Education and Communication (IEC): Education of the farmers on merit and demerits of Amantadine using every skill of information technology will be of great help to curb the use of this undesired drug.
Human resource development: The training and education of the Professionals and NGOs working in field is required to contribute in the education of community on the demerits of the use of Amantadine in poultry. This may be achieved through training of the trainers (ToT) both from public and private sectors to trickle down the information at community level.
Role of Pakistan Poultry Association (PPA): Great responsibility lies on PPA to keep an eye on the use of undesired medicines like Amantadine. Taking notice of this PPA may immediately call for a national seminar to discuss the consequences of the use of Amantadine in commercial poultry, arrive at conclusion, frame recommendation to be passed on to law makers and implementers in the Government.
Legislation: Role of Pakistan Veterinary Medical Council (PVMC) is of immense importance at this stage to come forward and offer a solution to the menace. Pvmc must lead and coordinate among pertinent quarters to promulgate a legislation to control such mal practices in the country.
The writer works at Centre for Poultry and Parasitology, PRI, Livestock and Dairy Development Department, Khyber Pukhtoonkhwa, Peshawar, Pakistan. He can be reached at firstname.lastname@example.org