The chicken or the egg? Exploring bi-directional associations between Newcastle disease vaccination and village chicken flock size in rural Tanzania

Newcastle disease (ND) is a viral disease of poultry with global importance, responsible for the loss of a potential source of household nutrition and economic livelihood in many low-income food-deficit countries. Periodic outbreaks of this endemic disease result in high mortality amongst free-ranging chicken flocks and may serve as a disincentive for rural households to invest time or resources in poultry-keeping. Sustainable ND control can be achieved through vaccination using a thermotolerant vaccine administered via eyedrop by trained "community vaccinators". This article evaluates the uptake and outcomes of fee-for-service ND vaccination programs in eight rural villages in the semi-arid central zone of Tanzania. It represents part of an interdisciplinary program seeking to address chronic undernutrition in children through improvements to existing poultry and crop systems. Newcastle disease vaccination uptake was found to vary substantially across communities and seasons, with a significantly higher level of vaccination amongst households participating in a longitudinal study of children's growth compared with non-participating households (p = 0.009). Two multivariable model analyses were used to explore associations between vaccination and chicken numbers, allowing for clustered data and socioeconomic and cultural variation amongst the population. Results demonstrated that both (a) households that undertook ND vaccination had a significantly larger chicken flock size in the period between that vaccination campaign and the next compared with those that did not vaccinate (p = 0.018); and (b) households with larger chicken flocks at the time of vaccination were significantly more likely to participate in vaccination programs (p < 0.001). Additionally, households vaccinating in all three vaccination campaigns held over 12 months were identified to have significantly larger chicken flocks at the end of this period (p < 0.001). Opportunities to understand causality and complexity through quantitative analyses are limited, and there is a role for qualitative approaches to explore decisions made by poultry-keeping households and the motivations, challenges and priorities of community vaccinators. Evidence of a bi-directional relationship, however, whereby vaccination leads to greater chicken numbers, and larger flocks are more likely to be vaccinated, offers useful insights into the efficacy of fee-for-service animal health programs. This article concludes that attention should be focused on ways of supporting the participation of vulnerable households in ND vaccination campaigns, and encouraging regular vaccination throughout the year, as a pathway to strengthen food security, promote resilience and contribute to improved human nutrition

Infection, colonization and shedding of Campylobacter and Salmonella in animals and their contribution to human disease: A review

Livestock meat and offal contribute significantly to human nutrition as sources of high‐quality protein and micronutrients. Livestock products are increasingly in demand, particularly in low‐ and middle‐income settings where economies are growing and meat is increasingly seen as an affordable and desirable food item. Demand is also driving intensification of livestock keeping and processing. An unintended consequence of intensification is increased exposure to zoonotic agents, and a contemporary emerging problem is infection with Campylobacter and Salmonella spp. from livestock (avian and mammalian), which can lead to disease, malabsorption and undernutrition through acute and chronic diarrhoea. This can occur at the farm, in households or through the food chain. Direct infection occurs when handling livestock and through bacteria shed into the environment, on food preparation surfaces or around the house and surroundings. This manuscript critically reviews Campylobacter and Salmonella infections in animals, examines the factors affecting colonization and faecal shedding of bacteria of these two genera as well as risk factors for human acquisition of the infection from infected animals or environment and analyses priority areas for preventive actions with a focus on resource‐poor settings

Public health risks of infection associated with bacterial pathogens of food safety importance in chickens in rural Tanzania

The chickens are colonised by and shed Campylobacter spp. and non-typhoidal Salmonella spp. which can be an important source of infection to humans. The most important source of Campylobacter and Salmonella infections in low- and middle-income countries, is thought to be close contact with live animals, and animal and human faecal contaminated environments. This arises as a result of unsafe water supply, and poor hygiene practices and sanitation. This study examined the risks that may contribute to the acquisition of animal-related foodborne pathogens in infants and young children in two rural districts of central Tanzania. Growth stage was commonly mentioned by questionnaire survey respondents (44.4%) as the main cause of diarrhoea in children under five years of age, among many causes listed. Among others, use of drinking water from open wells (OR = 0.46, 95% CI. 0.39 - 0.54; p < 0.001) and public tap (OR = 0.51, 95% CI. 0.44 - 0.61; p < 0.001) in the dry season was protective against childhood diarrhoea, compared to stream, river, pond or dam water. Sharing water sources with animals in the dry season (OR=1.48, 95% CI. 1.29 - 1.70; p < 0.001) and chickens roosting inside the home overnight (OR = 1.39, 95% CI. 1.20 - 1.60; p < 0.001) were associated with an increase in children diarrhoea incidences. Households headed by members of the Sukuma (p = 0.005) ethnic group and washing hands in running water (p = 0.007) were associated with higher height-for-age z-scores. Campylobacter jejuni, Campylobacter coli and Salmonella spp. were detected in chicken cloacal, latrine and kitchen floor swabs during dry and rainy seasons and several Salmonella serovars of public health importance were isolated from chickens. Prevention of gastrointestinal infections of animal origin should be directed at improving local water supplies, hygiene practices and sanitation, and introducing good animal husbandry skills which consider available resources and existing cultural practices

Biosecurity in Village and Other Free-Range Poultry—Trying to Square the Circle?

Village poultry commonly suffer significant disease related losses and a plethora of biosecurity measures is widely advocated as a means to reduce morbidity and mortality. This paper uses a household economy perspective to assess some “economic” considerations determining biosecurity investments of village poultry keepers. It draws on the 2012/13 Tanzania National Panel Survey (TZ-NPS), which covered 1,228 poultry-keeping households. Disease was the most frequently reported cause of bird losses and, in the majority of households, accounted for more than half of reported bird losses. However, given that poultry rarely contributed more than 10% to total annual household income, for 95% of households the value of birds lost to disease represented &amp;lt;10% of annual income. The value placed on poultry within households may vary by gender and the overall figure may mask differential intra-household impacts. The break-even cost for various levels of reduction of disease losses is estimated using a partial budget analysis. Even if achieved at no cost, a 75% reduction in disease-associated mortality would only result in a one percent increase of annual household income. Thus, to the “average” village poultry-keeping household, investments in poultry may not be of high priority, even when cost-effective. Where risks of disease spread impact on the wider community and generate significant externalities, poultry keepers must be supported by wider societal actions rather than being expected to invest in biosecurity for purely personal gain.</jats:p

Overview of household characteristics, by ward.

<p>Overview of household characteristics, by ward.</p

<i>Campylobacter</i> and <i>Salmonella</i> in Scavenging Indigenous Chickens in Rural Central Tanzania: Prevalence, Antimicrobial Resistance, and Genomic Features

Introduction: Salmonella and Campylobacter spp. are commonly reported bacterial foodborne pathogens causing morbidity and mortality worldwide. In rural areas, where there is a high occurrence rate of human–animal interactions and poor hygiene practices, shedding animals present a high risk to humans in acquiring animal-associated infections. Materials and methods: Seasonal prevalence of Campylobacter jejuni, Campylobacter coli, and Salmonella spp. in scavenging indigenous chicken faeces was determined by polymerase chain reaction (PCR). Antimicrobial resistance was studied in Salmonella isolates by disc diffusion method, and whole-genome sequenced isolates were used to determine Salmonella serovars, antimicrobial resistance genes, virulence genes, and plasmid profile. Results: The overall prevalence of Campylobacter in chickens was 7.2% in the dry season and 8.0% in the rainy season (p = 0.39), and that of Salmonella was 11.1% in the dry season and 16.2% in the rainy season (p = 0.29). Salmonella serovars detected were II 35:g,m,s,t:-, Ball, Typhimurium, Haardt/Blockley, Braenderup, and Enteritidis/Gallinarum. One S. II 35:g,m,s,t:- isolate was resistant to ampicillin and the rest were either intermediate resistant or pansusceptible to the tested antimicrobials. The resistance genes observed were CatA, tetJ, and fosA7, most common in Ball than in other serovars. Seven plasmids were identified, more common in serovar Ball and less common in II 35:g,m,s,t:-. Serovar II 35:g,m,s,t:- isolates were missing some of the virulence genes important for Salmonella pathogenicity found in other serovars isolated. Conclusion: PCR detection of Campylobacter spp. and Salmonella spp. in chickens necessitate the improvement of hygiene at the household level and reducing human–chicken interaction as a strategy of preventing humans from acquiring chicken-associated bacteria, which would enter the human food chain. Infrequent use of antimicrobials in this type of poultry is most likely the reason for the low rates of antimicrobial resistance observed in this study

Percentage of enrolled households keeping chickens consistently, intermittently or not at all, during two consecutive twelve-month periods in Sanza and Majiri Ward.

<p>95% confidence intervals are shown.</p

Overview of administrative units in study population, with the number of enrolled households in each of eight villages, and aggregated at ward and district levels.

<p>The timing of vaccination campaigns is shown.</p