3.1 Field epidemiological observations
During the OIE reporting period of January to December 2021, 223 outbreaks were detected in the DR for which there were 16,373 susceptible animals, 9,617 cases, 8,336 “killed or disposed of”, and 7,449 deaths. Premises experiencing outbreaks represented a variety of production systems, including commercial and backyard smallholder farms. The population on each premises ranged between 1 and 1,700 pigs. While insufficient data were available for a detailed epidemiological analysis, morbidity and mortality were able to be calculated for this OIE reporting period. Overall morbidity was 58.7%, mortality 45.5%, and case mortality 77.5%; morbidity on premises varied widely from 1-100%. We note that these metrics were calculated from passive surveillance data and may be biased due to the lack of a statistically sound sampling strategy.
Several farms from which samples were positive by PCR between May and July had reported high mortality rates to DR officials. However, field observations included a variety of clinical presentations, ranging from the typical peracute presentation of Georgia 2007/1 ASFV to subclinical and chronic presentations, more indicative of an attenuated ASFV strain. In acute cases, pigs were described as presenting with some combination of ataxia, anorexia, nasal and ocular discharge, vomiting, abortion, cyanosis, pyrexia, lethargy, diarrhea, and diffuse dermal changes typical of hemorrhagic fevers. Swine with subacute presentations reportedly exhibited non-specific signs, such as depression, weight loss, and anorexia, and either died after a long period of time or survived at a higher rate than is typical for virulent strains of ASFV (Gonzales et al., 2021). A small number of infected animals presented with abortion as the only symptom or were asymptomatic at the time of sampling.