The burden of Streptococcus suis infection in humans is increasing worldwide. In Thailand, S. suis is the second most commonly recorded zoonosis. The principal sources of human S. suis infection are pig and pork products. A detailed understanding of the epidemiological characteristics of S. suis and the burden of the disease may help improve prevention and control policy to reduce the burden of this bacterial infection. The work presented in this thesis focuses on human outbreaks of S. suis in Chiang Mai, Thailand, in humans and backyard pigs. This thesis examined the characteristics of previous outbreaks of S. suis in humans and calculated the incidence, disease burden and the associated economic burden of S. suis infection in Chiang Mai. The backyard pig system is important for S. suis transmission and this thesis examined the characteristics of the backyard pig production system in Chaing Mai and examined the prevalence and risk factor for S. suis infection in pigs. Finally, to examine transmission of S. suis, isolates collected during this study were identified and subject to molecular characterization. A retrospective analysis of surveillance data for S. suis cases in Chiang Mai between 2005 to 2014 highlighted the annual incidence rate over this ten year period of 15.52 per 1,000,000 population, 6.5 times higher than for the rest of Thailand (2.37 per 1,000,000 population). The case fatality rate was high at 10.12%. The impact on human health of S. suis infection was derived from surveillance data for the year 2013. The health burden measured in term of Disability Adjusted Life Years (DALYs) was estimated at 7.41 per 100,000 population. Most of the health burden (98.28%) was in adults aged 15-64 years. Males had 3.5 times the health burden of females. The consequences of hearing loss and deafness had significant impacts on affected individuals quality of life. The economic impact of S. suis outbreaks in Chiang Mai was between 2013 and 2014 was estimated from interview data. Most patients were covered for their health costs by the national health security scheme, with expenditure due to S. suis on average being 37,955 baht (£759) per patient. Out of pocket expenses for individuals and their families averaged 5,198 baht (£104) per patient. An epidemiological survey of backyard pig production facilities was undertaken in Chiang Mai province where there was a reported high incidence of S. suis cases in humans occurred each year. Most holdings had between one to five pigs and all holdings shared similar characteristics and management practices. The prevalence of S. suis was in pigs was 4.8% (95%CI=2.2-7.4%). Pigs living in larger spaces (≥ 1.2 m2) showed a lower risk for S. suis infection (OR = 4.35, 95% CI = 1.07-25.21). Examination of the isolates from this study revealed a diversity of serotypes. Only one isolate was identified as S. suis serotype 9. The rest did not match any common serotypes for S. suis (1, 2, 7 or 9) and known virulent strains were not identified. Twelve independent sequence profiles were determined by MLST, of which, 11 were novel. Backyard pigs were found to be commonly infected with a range of previously unidentified S. suis and may be a significant reservoir of human infection.

The Pampanga province is one of the largest pork-producing provinces in the Philippines. Half of the province's pigs are reared in so-called back-yard farms. At these farms, there are no regulations regarding manure management and because of this, large amounts of manure are dumped close to the stables. These actions lead to spontaneous emission of greenhouse gases, eutrophication of rivers and groundwater pollution. In addition, the spread of manure contributes to inadequate sanitation and increased risks of disease among the inhabitants of the province. LPG and wood are the most popular fuels for cooking in the Philippines. LPG is most common in the cities, while more than 60 percent of the rural population still relies on firewood for cooking. LPG is a fossil fuel that, when burned, contributes to an enhanced greenhouse effect. The use of wood increases the pressure on the local biomass and increases the risk of lung diseases for the user. Anaerobic digestion of pig manure under contributes to a more sustainable manure management. At the same time, energy in form of biogas is produced. Biogas is a renewable energy source, which is considered carbon neutral. If pig manure is co-digested with kitchen waste, a more efficient and stable digestion process may be achieved. This study aims to contribute to sustainable development at backyard pig farms in the Pampanga province by demonstrating how pig manure and kitchen waste can be utilized for biogas production. In order to develop an appropriate composition of pig manure and kitchen waste for anaerobic digestion, batch digestion of pig manure and kitchen waste was performed at laboratory scale. During a field study, the substrate composition was digested in test plants under local conditions in Pampanga. During the field study, several field trips to backyard pig farms were performed. Based on prevailing conditions and available materials in the province, a full-scale biogas digester was designed. The digester was sized to produce enough biogas to fulfil one family’s daily requirement of cooking fuel. If the daily biogas production reaches 2.5 m3 it is possible to replace 178 kg LPG or 9855 kg of firewood every year. The reduction of LPG prevents 2700 kg carbon dioxide equivalents from being emitted to the atmosphere every year. The reduction of LPG use also results in an annual saving of 9062 PHP (1672 SEK) for a family. This number corresponds to 11 procent of the total investment cost of the digester. / Pampangaprovinsen är en av de största producenterna av fläskkött i hela Filippinerna. Hälften av provinsens grisar föds upp på så kallade backayard farms. På dessa gårdar finns inga restriktioner gällande gödselhantering. Därför dumpas stora mängder gödsel i gårdarnas närområde vilket leder till spontana utsläpp av växthusgaser, övergödning i vattendrag och förorenat grundvatten. Dessutom leder spridning av gödslet till försämrad hygien och ökad sjukdomsspridning bland provinsens invånare. Gasol och ved är de mest populära bränslena för matlagning i Filippinerna. Gasol är mest utbrett i städerna medan drygt 60 procent av landsbygdens befolkning fortfarande förlitar sig på ved vid matlagning. Gasol är ett fossilt bränsle som vid förbränning bidrar till en förstärkt växthuseffekt. Användning av ved ökar trycket på den lokala biomassan och vid förbränning är risken för sjukdomar i luftvägarna hos användaren stor. Anaerob rötning av grisgödsel möjliggör en mer hållbar gödselhantering samtidigt som energi i form av biogas produceras. Biogas är en förnyelsebar energikälla som dessutom anses vara koldioxidneutral. Grisgödsel kan med fördel samrötas med matavfall för att uppnå en effektivare och mer stabil rötprocess. Den här studien syftar till att bidra till hållbar utveckling inom Pampangaprovinsens backyard pig farms genom att demonstrera hur grisgödsel tillsammans med matavfall kan användas för biogasproduktion. Under studiens inledande del utfördes satsvis rötning av grisgödsel och matavfall i laborativ skala, i syfte att ta fram en lämplig sammansättning av de båda substraten. Substratsammansättningen rötades därefter i testanläggningar vid lokala förhållanden under en fältstudie i Pampangaprovinsen. Under fältstudien genomfördes även studiebesök till olika backyard pig farms. Baserat på rådande förhållanden och tillgängliga material i provinsen designades slutligen en rötkammare. Rötkammaren dimensionerades så att den kunde förse en familj med bränsle för matlagning. Om den dagliga biogasproduktionen når 2.5 m3 är det möjligt att ersätta 178 kg gasol eller 9855 kg ved per år. Minskningen av gasol resulterar i en årlig reducering av växthusgasutsläpp med minst 2700 kg koldioxidekvivalenter. Minskningen av gasol resulterar också i en årlig besparing på 9062 PHP (1672 SEK). Denna siffra motsvarar 11 procent av den totala investeringskostnaden för rötkammaren.