**3.6 Factors supporting occurrence of outbreaks**

Following initial introduction of the virus from a possible migratory wild bird [22] or water fowl [20] through direct means into commercial poultry or by resident water fowls and ducks that form bridges of virus transmission from migratory wild birds [35], the virus is further spread by inadequate farm biosecurity, trade in poultry, human and vehicular exchanges between farms, and uncontrolled farm visits by poultry and poultry product vendors. Live bird markets have also been shown to harbor [39] and transmit the virus among birds and finally to household poultry upon introduction of poultry bought from live bird markets [20]. Mixed-species poultry farming has been shown to have higher odds of HPAI virus infection [39] and could harbor apparently healthy but infected duck species which may transmit the virus to susceptible chickens and turkeys. In a study conducted during the first introduction of HPAI into Nigeria, it was shown that mortality rate was much higher in mixed species flocks (*P* < 0.0001) and ranged from 4.92 to 73.15% with the chicken-duck-turkey mixed flock farms having the highest rate (73.15%) [39]. Also, it was established that higher risk of HPAI disease occurred in multiple, mixed species poultry than in single species poultry production [39]. **Figure 3** depicts a typical live bird scenario.

## **3.7 Control measures**

Enforcement of movement control, surveillance (active and passive), and prompt payment of the revised compensation to the affected farmers, including reorganization of the LBMs which led to the successes recorded during the

**67**

**Figure 4.**

*received anonymously.*

*Features of Highly Pathogenic Avian Influenza (HPAI) H5N1 in Domestic Poultry*

2006–2007 epizootics [45], is necessary to control HPAI in Nigeria. In these current HPAI epizootics, it has been observed that coordination and other instituted control measures, including biosecurity and compensation of affected farmers, seem to be less rigorous, and this may explain the rapid spread from the index cases to 25 states

**4. Clinicopathologic features of avian influenza infection in domestic** 

Three possible clinical outcomes have been shown to occur with AI infection in birds: there may be no clinical signs, it may result in a mild disease, and severe disease with death may occur [3]. Virus replication within the cell, tissue, organ, or a combination results in pathobiological changes which are abnormal physiological and anatomic changes. Therefore, in general, as virus replication titers increase, so do the severity of pathobiological changes such as gross and microscopic lesions with the most pathogenic virus strains causing major cell damage and death if it is

In gallinaceous domestic poultry, infection with HPAI viruses produces severe depression, severe decrease in feed and water consumption, high morbidity and mortality rates, sudden death, and occasionally nervous signs if they survive the peracute syndrome. However, the frequency of clinical signs and gross lesions varies with virus and species of bird and is not consistent in all birds [3] (**Figure 5**).

Individual birds are listless and exhibit edema; cyanosis of the comb, wattles, and legs; and diarrhea. Sudden deaths without any symptoms may also occur. Signs observed and reported are sudden death, high mortality, weakness, and

*(A) An open-sided layer chicken pen infected with highly pathogenic avian influenza virus. (B) The flock in A when the pen was already depopulated. (C) The poultry birds been placed in an open dug pit after depopulation. (D) The flock in A been burnt after depopulation. A and B courtesy of Dr. Luka Pam; C and D* 

**commercial and rural poultry: chickens and ducks**

sufficiently severe to affect critical organs [3] **Figure 4**.

*DOI: http://dx.doi.org/10.5772/intechopen.86098*

of the federation as of March 2016 [42].

**4.1 General outcome of disease**

**4.2 Clinical signs**

*4.2.1 Chickens*

*Features of Highly Pathogenic Avian Influenza (HPAI) H5N1 in Domestic Poultry DOI: http://dx.doi.org/10.5772/intechopen.86098*

2006–2007 epizootics [45], is necessary to control HPAI in Nigeria. In these current HPAI epizootics, it has been observed that coordination and other instituted control measures, including biosecurity and compensation of affected farmers, seem to be less rigorous, and this may explain the rapid spread from the index cases to 25 states of the federation as of March 2016 [42].
