Epidemiology, risk factors and diagnostic accuracy of surveillance methods of selected diseases presenting with respiratory signs in small ruminants in Tanzania

Abstract

Outbreaks of diseases presenting with respiratory signs in small ruminants in Tanzania have been reported for years. Concurrent infections complicate diagnosis resulting in untimely interventions and significant economic losses. A cross-sectional survey was conducted between June, 2016 and July, 2017 to determine the risk factors associated with small ruminants exposure to Mycoplasma capricolum subsp. capripneumoniae (M. capripneumoniae) and small ruminant morbillivirus (SRMV). Outbreak investigations were conducted between June, 2016 and July, 2018 to validate the performance of the existing and improved disease surveillance systems and to evaluate the accuracy of the reports, the data were also used to determine the level of concurrent infections in those outbreaks. Risk factors data were analysed using logistic regression models. The field data forms (FD-1 and FD-2) performance were analysed using inter-rater reliability test against the gold standard test. The percentage proportions were used to describe levels of concurrent infections. Risk factors for M. capripneumoniae occurrence in goats were farming system (OR = 0.91073332), mixing species (OR= 1.0793679) and grazing with wild animals (OR=1.0546803). Occurrence of SRMV in goats was influenced by farming system (OR=1.154254), mixing of flocks (OR=1.060278) and grazing with wild animals (OR=1.077164). Risk factors for occurrence of M. capripneumoniae in sheep were farming system (OR=0.9310771) and presence of PPR (OR=1.0564274) whereas, SRMV was influenced by farming system (OR=1.188681), mixing flocks (OR=1.135146) and previous diseases outbreak (OR=1.161883). In outbreak investigations, FD-2 performed better than FD-1 in the diagnosis of both CCPP (PPV = 22.2% Vs 16.2%) and PPR (PPV = 50.0% Vs 43.2%) in goats and in sheep, in the diagnosis of PPR (PPV = 26.3% Vs 23.1%). In determining concurrent infections, 79.1% (117/148) of the goats and 28.1% (16/57) of the sheep had concurrent infections. The SRMV and Pasteurella multocida (P. multocida) in goats and SRMV in sheep were the pathogens involved in co-infections. This study reports several risk factors being associated with exposure of small ruminants to M. capripneumoniae and SRMV and that, the current disease surveillance system does not provide reliable accurate data on outbreaks with co-infections in which P. multocida are involved and should be considered in control strategies.