Tuberculosis epidemiology in islands: insularity, hosts and trade

Environmental DNA: A promising factor for tuberculosis risk assessment in multi-host settings

Attaining and maintaining the Official Tuberculosis Free status continues to be a challenge when several domestic and wild hosts contribute to the maintenance of the Mycobacterium tuberculosis complex (MTC). Local tuberculosis hotspots are sometimes identified in cattle in low-prevalence regions. We have, therefore, studied one such hotspot in depth in order to produce an epidemiological diagnosis. Host population size and MTC prevalence were estimated in selected wildlife and in livestock, while on-cattle environmental DNA detection was additionally used as a proxy for risk of exposure at the farm (herd) level. Positive skin test reactors were found on16 of the 24 cattle farms studied in the period 2012–2016. Although all goats tested negative to the skin test during this period, MTC was confirmed in four sheep at slaughter, thus indicating an unknown prevalence of infection in this host species. With regard to wildlife, the prevalence of MTC infection based on culture was 8.8% in the case of wild boar (Sus scrofa), and the only road-killed badger (Meles meles) submitted for culture tested positive. Two criteria were employed to divide the cattle farms into higher or lower risk: tuberculosis testing results and environmental DNA detection. Environmental MTC DNA detection yielded significant differences regarding “use of regional pastures” and “proximity to woodland”. This study suggests that on-animal environmental DNA sampling may help when assessing contact risk as regards MTC in livestock at the herd level. This tool opens up new avenues of epidemiological research in complex multi-host settings.

Newly registered tuberculosis: A comparison of rate and success of management in two island districts with different in accessibility of transportation in Thailand

Background

Tuberculosis is an important infection that can be seen in several countries. The occurrence of disease in the remoted setting is an interesting issue that is an actual challenge for management. Here, the authors present and discuss on the newly registered tuberculosis cases in two island districts of Thailand, a tropical endemic country in Southeast Asia.

Methods

The authors hereby retrospectively analyzed registered data of newly registered tuberculosis cases in two island districts with different in accessibility of transportation in Thailand. A comparison of rate and success of management was made.

Results

According to the statistical analysis, there is a significant difference of incidence rates of newly registered tuberculosis cases between the two island districts (0.13% vs. 0.04%). There is also a significant difference of successful antituberculosis drug management rates between the two island districts (72.7% vs. 100%).

Conclusion

The island district with easier accessibility by transportation has a more number of newly registered tuberculosis case and a less success rate of antituberculosis drug treatment.

Molecular epidemiology of mycobacteria among herds in Marajó Island, Brazil, reveals strains genetically related and potential zoonotic risk of clinical relevance

Mycobacterium bovis is the main causative agent of bovine tuberculosis (bTB) being among the animal-adapted Mycobacterium tuberculosis complex. Herds can also be infected with non-tuberculous mycobacteria (NTM) causing a negative effect on the economy and on animal and human health through zoonotic infections. Molecular tools are required for mycobacteria identification; thus, it is laborious to determine the epidemiological information of mycobacteria among herds. We aimed to describe the mycobacterial pathogens associated with cases of suspected bTB lesions in cattle/buffaloes slaughtered for consumption and to investigate bTB transmission. We evaluated 74 lesion samples from 48 animals (27 bovine/21 buffaloes) from 16 mapped farms. Positives samples from nested-PCR were cultured in Lowenstein-Jensen (LJ), 2% pyruvate (LJ + P), and 2% glycerol (LJ + G) media, followed by Ziehl-Neelsen (ZN) staining technique and partial gene sequencing (hsp65, rpoB, and 16S-rRNA). Spoligotyping and 24-MIRU-VNTR were performed. The LJ + P increased the chance of obtaining bacilli. The respiratory tract and the oral cavity were the most important infection route. In addition, the calcified part of the lesions suggested chronic bTB. Spoligotypes of M. bovis (SIT986/SB0885) differed from others found in South America, and the MIRU-VNTR 24 loci suggested that bTB was associated to highly related strains. The NTM species found are of clinical importance in humans.

"Moving like birds": A qualitative study of population mobility and health implications in the Bijagós Islands, Guinea Bissau

Population movement is a major driver for infectious disease transmission and can impact the success of disease control and elimination strategies. The relationship between disease transmission and permanent migration is well documented, but fewer studies have considered how different types of population mobility affects disease transmission and control programmes. This qualitative study was conducted on two islands of the Bijagós archipelago, Guinea Bissau to understand spatial and temporal population movement, and reasons for these movements, within, between and away from the Bijagós islands. Data were collected on two islands using key informant interviews (n = 8), daily activity-location interviews (n = 30) and focus group discussions (n = 6). Data were analysed thematically using an adapted typology of mobility. Findings revealed that movement within and between islands, and from islands to the mainland, was a common feature of island life for men and women alike. It was usual for trips away from home to last for several months at a time. Five key reasons for travel were identified: subsistence activities; family events; income generating activities; cultural festivities and healthcare. These movements often occurred erratically all year round, with the exception of seasonal travel within and between islands for agricultural purposes. Our study characterised detailed patterns of human mobility in the Bijagós islands as a first step towards understanding the potential impact of different types of mobility on disease exposure, transmission and public health programmes. Short-term mobility may have a significant impact on the spread of infectious diseases with short incubation periods. Predictable movements, such as travel for seasonal agricultural work, should be taken into account for tailoring and increasing the reach of public health interventions. Further research is needed to understand the role of human behaviour and mobility in disease transmission and control across the archipelago.

Bovine Tuberculosis in Britain and Ireland - A Perfect Storm? the Confluence of Potential Ecological and Epidemiological Impediments to Controlling a Chronic Infectious Disease

Successful eradication schemes for bovine tuberculosis (bTB) have been implemented in a number of European and other countries over the last 50 years. However, the islands of Britain and Ireland remain a significant aberration to this trend, with the recent exception of Scotland. Why have eradication schemes failed within these countries, while apparently similar programs have been successful elsewhere? While significant socio-economic and political factors have been discussed elsewhere as key determinants of disease eradication, here we review some of the potential ecological and epidemiological constraints that are present in these islands relative to other parts of Europe. We argue that the convergence of these potential factors may interact additively to diminish the potential of the present control programs to achieve eradication. Issues identified include heterogeneity of diagnostic testing approaches, the presence of an abundant wildlife reservoir of infection and the challenge of sustainably managing this risk effectively; the nature, size, density and network structure of cattle farming; potential effects of Mycobacterium bovis strain heterogeneity on disease transmission dynamics; possible impacts of concurrent endemic infections on the disclosure of truly infected animals; climatological differences and change coupled with environmental contamination. We further argue that control and eradication of this complex disease may benefit from an ecosystem level approach to management. We hope that this perspective can stimulate a new conversation about the many factors potentially impacting bTB eradication schemes in Britain and Ireland and possibly stimulate new research in the areas identified.

Molecular epidemiology of Mycobacterium tuberculosis complex strains isolated from livestock and wild animals in Italy suggests the need for a different eradication strategy for bovine tuberculosis

Bovine tuberculosis (bTB) is an important zoonosis, which has been re-emerging in different ecological scenarios. In Sicily, Italy, from 2004 to 2014, an anatomopathological survey for tuberculosis-like lesions both in farmed and wild animals was performed. The isolates were genotyped using spoligotyping and Mycobacterial Interspersed Repetitive Units-Variable Number of Tandem Repeats (MIRU-VNTR) techniques. High prevalence of lesions was observed for cattle (4%), pigs (4.9%) and wild boars (6.8%), and a total of 625 Mycobacterium bovis isolates were identified. Genotyping analysis showed the presence of 37 different spoligotypes including fifteen spoligotypes not present in other Italian regions and 266 MIRU-VNTR profiles. Spoligotype SB0120 exhibited the highest prevalence in cattle (50%) and pigs (56%) and the highest genetic variety with 126 different MIRU-VNTR profiles. The isolation of M. bovis in a farmer underlines the importance of M. bovis identification during the human TB diagnostic processes. This study supported the use of the genotyping analysis as a valuable tool for the evaluation of the epidemiological role of pigs and other domestic reservoirs such as goats and the role of wildlife in the maintenance of bTB infection.

Spoligotype diversity and 5-year trends of bovine tuberculosis in Extremadura, southern Spain

Bovine tuberculosis (bTB) causes significant losses to farming economies worldwide. A better understanding on the epidemiology of this disease and the role that the different hosts develop in the maintenance and spread of bTB is vital to control this zoonotic disease. This study reports the spoligotype diversity and temporal evolution of Mycobacterium tuberculosis Complex (MTBC) isolates obtained from Extremadura (southern Spain). Genotyping data of Mycobacterium bovis (n = 2102) and Mycobacterium caprae (n = 96) isolates from cattle and wildlife species, collected between 2008 and 2012, were used in this study. The isolates resulted clustered into 88 spoligotypes which varied largely in frequency and occurrence in the three hosts. The 20 most frequent patterns represented 91.99 % of the isolates, the spoligotype SB0121 being the clearly predominant and most widely dispersed geographically. The major variety of the spoligotype patterns (78 out of 88) was isolated from the cattle, in fact 50 (56.83 %) of the patterns were found only in this species. Within the spoligotypes shared between the cattle and wildlife species, 17 patterns (1747 isolates) were shared with wild boar and Iberian red deer, 10 patterns (308 isolates) were exclusively shared with wild boar, and only one pattern (two isolates) was shared exclusively with Iberian red deer. The significant number of spoligotypes shared between the three hosts (79.49 %) highlights the components of the multi-host system that allows the bTB maintenance in our study area. The greater percentage of isolates shared by the wild boar and cattle (93.50 %) supports the role of wild boar as main maintenance host for bTB in cattle. These results could be extrapolated to areas with a similar epidemiological scenario and could be helpful for other countries where wild reservoirs represent a handicap for the successful eradication of bTB from livestock.

The role of wildlife in bluetongue virus maintenance in Europe: lessons learned after the natural infection in Spain

Bluetongue (BT) is a re-emergent vector-borne viral disease of domestic and wild ruminants caused by bluetongue virus (BTV), a member of the genus Orbivirus. A complex multi-host, multi-vector and multi-pathogen (26 serotypes) transmission and maintenance network has recently emerged in Europe, and wild ruminants are regarded as an important node in this network. This review analyses the reservoir role of wild ruminants in Europe, identifying gaps in knowledge and proposing actions. Wild ruminant species are indicators of BTV circulation. Excepting the mouflon (Ovis aries musimon), European wild ungulates do not develop clinical disease. Diagnostic techniques used in wildlife do not differ from those used in domestic ruminants provided they are validated. Demographic, behavioural and physiological traits of wild hosts modulate their relationship with BTV vectors and with the virus itself. While BTV has been eradicated from central and northern Europe, it is still circulating in the Mediterranean Basin. We propose that currently two BTV cycles coexist in certain regions of the Mediterranean Basin, a wild one largely driven by deer of the subfamily Cervinae and a domestic one. These are probably linked through shared Culicoides vectors of several species. We suggest that wildlife might be contributing to this situation through vector maintenance and virus maintenance. Additionally, differences in temperature and other environmental factors add complexity to the Mediterranean habitats as compared to central and northern European ones. Intervention options in wildlife populations are limited. There is a need to know the role of wildlife in maintaining Culicoides populations, and to know which Culicoides species mediate the wildlife-livestock-BTV transmission events. There is also a clear need to study more in depth the links between Cervinae deer densities, environmental factors and BTV maintenance. Regarding disease control, we suggest that research efforts should be focused on wildlife population and wildlife disease monitoring.

Evaluating the tuberculosis hazard posed to cattle from wildlife across Europe

Tuberculosis (TB) caused by infection with Mycobacterium bovis (M. bovis) and other closely related members of the M. tuberculosis complex (MTC) infects many domestic and wildlife species across Europe. Transmission from wildlife species to cattle complicates the control of disease in cattle. By determining the level of TB hazard for which a given wildlife species is responsible, the potential for transmission to the cattle population can be evaluated. We undertook a quantitative review of TB hazard across Europe on a country-by-country basis for cattle and five widely-distributed wildlife species. Cattle posed the greatest current and potential TB hazard other cattle for the majority of countries in Europe. Wild boar posed the greatest hazard of all the wildlife species, indicating that wild boar have the greatest ability to transmit the disease to cattle. The most common host systems for TB hazards in Europe are the cattle-deer-wild boar ones. The cattle-roe deer-wild boar system is found in 10 countries, and the cattle-red deer-wild boar system is found in five countries. The dominance of cattle with respect to the hazards in many regions confirms that intensive surveillance of cattle for TB should play an important role in any TB control programme. The significant contribution that wildlife can make to the TB hazard to cattle is also of concern, given current population and distribution increases of some susceptible wildlife species, especially wild boar and deer, and the paucity of wildlife TB surveillance programmes.