**7. Conclusions**

*Viruses and Viral Infections in Developing Countries*

Ghana, Cameroon, and Togo [42].

ing the Federal Capital Territory (Abuja) [42].

death of an average aged woman [38].

**6. Endemic situation**

[55, 56].

**5. Persistence of avian influenza viruses in poultry population**

Many countries and regions have successfully controlled the virus after its occurrence, whereas some other countries face occasional reoccurrences despite intensive control efforts [50]. By the last quarter of 2007, outbreaks of HPAIV in Nigeria appeared to have been successfully controlled by measures such as "stamping out with compensation," restrictions on movement of poultry, and enhanced surveillance [19]. But the detection of new cases of HPAIV in farms from Kano and Katsina States and in apparently healthy ducks in live bird markets in Gombe and Kebbi States [19, 22, 51] proved otherwise. The viruses in sublineage H which were isolated from vultures, pigeon, guinea fowl, free-range chicken, and other birds from a wildlife park were observed to be geographically and chronologically dispersed in Nigeria following infection of the LBMs. Thus, the importance of the live bird markets in the spread of the virus in West Africa is particularly evident [52]. Also, a resurgent outbreak was recorded in January 2015, after almost 8 years following the end of the last epizootics, [39, 41]. Thus far, the outbreak has spread to several other African countries including Burkina Faso, Cote d'Ivore, Niger,

Influenza A viruses are known to circulate in their natural hosts and wild aquatic

The circulation and reemergence of highly pathogenic avian influenza viruses of H5N1 subtype (HPAIV-H5N1) raise major concerns in public health and poultry industries [57]. Tens of millions of birds have died of HPAIV-H5N1 in the global poultry industry, and hundreds of millions of poultry have been slaughtered to control the spread of the virus [58]. Urgent revised control measures are required to stem waves of outbreaks and to prevent the virus from becoming enzootic in poultry if the ongoing trend of recent outbreaks in Nigeria persists, [42]. If not, this may result in severe public health consequences, as observed in countries where the virus has become enzootic in poultry [59]. In a little over a year of the reported resurgent into Nigeria, several waves of outbreaks were reported in 25 states includ-

Following the detection and reporting of highly pathogenic avian influenza (HPAI) H5N1 virus (clade 2.2) in Nigeria in 2006 [28] and subsequently in other parts of Africa, 11 countries in the region had reported outbreaks in poultry within a few months of its detection and eventually became enzootic in Egypt's poultry [60] causing human deaths. By July 2016, the human cases as a result of infection with HPAI H5N1 in Djibouti, Nigeria, and Egypt stand at 1, 1, and 354 people, respectively, with Egypt having the second highest number of human deaths among countries with H5N1 infections in the world [61]. The exposure of humans at the human-animal interface enzootic circulation of highly pathogenic avian influenza virus (HPAIV) in agricultural scenarios poses one of the greatest public health concerns [41]. The only human case in Nigeria, which was officially reported by the World Health Organization on February 3, 2007, was diagnosed following a thorough investigation of a fever complicated by respiratory distress which finally led to

birds predominantly of the orders Anseriformes (ducks, geese and swans) and Charadriiformes (gulls, waders, and terns). These wild ducks are natural reservoirs of avian influenza (AI) viruses [10, 53, 54], and epidemiologic evidence and experimental infections show that domestic ducks are also susceptible to AI viruses

**70**

The H5 and H7 subtypes associated with the highly pathogenic form of AI (HPAI), an extremely virulent virus which causes up to 100% mortality in domestic poultry, need special efforts to ensure eradication. Bearing in mind that the intensive poultry production units are an ideal viral breeding ground for these forms of AI, all factors that enhance this propensity should be giving the attention required. A critical look at the Nigerian HPAI situation not only revealed the general clinicopathologic features in domestic poultry and factors that support the persistence of the virus in the environment but also gave insight to the flow of the virus in the country. A situation whereby poultry are kept in free-range, multispecies, multiage holdings with low biosecurity supports the spread of HPAI. Also, the LBMs that have been fed by this unorganized poultry structure have consistently been the nidus for HPAI detection, be it in 2008 after the virus was thought to have been eradicated or in 2015, when the virus resurfaced in Kano and Lagos. It is therefore important that the strict biosecurity measures that ensure prevention of HPAI incursion into poultry premises after 2008 are revamped while improving on the organization of the poultry and product supply chain in the country.
