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.