Disease pattern and Seasonal occurrence
Movement of animals from one region to other with in the same country or transboundary is determining factor of disease occurrence. In dry season, animals usually travel long distance in search of fodder and water (Nanda et al., 1996). In humid areas, PPR always occurred in an epizootic form with 80–90 % morbidity and 50–80 % mortality. PPR is often fatal and usually occur as a subclinical in arid and semi-arid areas (Lefevre & Diallo, 1990). Young animals between age of three to four months are more susceptible to PPRV (Srinivas & Gopal, 1996) due to decrease in natural immunity (maternal antibodies) (Saliki et al., 1993). There is constant circulation of virus between ages of 4 to 24 months (Taylor et al., 1979). High morbidity and mortality have been reported in all of the age groups (Abu Elzein et al., 1990). Abubakar et al. (2009) reported that prevalence of PPR in small ruminants in Pakistan is 40.98 % and disease is severe in goats mostly. Zahur et al. (2011) found a higher prevalence in goats (52.9) than in sheep (37.7 %) in Pakistan while Singh et al. (2009) reported an almost similar prevalence for sheep (36.3 %) and goats (32.4 %) in India. A field survey in Nigeria showed that the disease rate of PPR in sheep (57 %) appears to be more than that in goats (44 %) (Taylor and Abegunde), (1979). So in short a regions discrepancy about disease severity is present across the globe and more is linked to regional environment as well as animal breeds and socioeconomic status of nomadism and local farmers.
In addition, PPR-associated abortions could occur in PPRV-infected pregnant dams. Abubakar et al. (2008) has reported that serum samples from the aborted dams found positive for PPRV antibodies so the PPR disease has a possible association of mortality and prevalence with high rate of abortions in goat. Moreover, if the animal is infected with PPRV abortions may occur at any stage of gestation. This leads toward economic losses and discourage the farmer communities.
PPR occurrence is affected by Climatic factors. In rainy season outbreaks minimized due to decreased movement of animals as more fodder availability and increase nutritional and health status. In Dec-Feb the dry and dusty season in combination with poor nutrition cause disease spread and cases get peak in April. In Pakistan, Khan et al. (2008) reported high PPR seroprevalence in December to February and September and October while Abubakar et al. (2009) reported the disease frequency greater in January to April and 33 % of cases reported in March. So we may say that the disease occurrence is throughout the year with the severity variation in different weathers. A study conducted in china regarding patterns of seasonality of disease which were characterized by peaks in April of 2014 (Gao et al., 2019). According to (Obi et al., 1983; Durojaiye et al., 1983 and Abubakar et al., 2011), most cases of PPR emerge with the start of summer season and cases get peak during the months of April to July and then the prevalence drop again that indicate the temporal pattern of disease.