A review of geospatial and ecological factors affecting disease spread in wild pigs: considerations for models of foot-and-mouth disease spread

Around the world, wild boar or feral pigs are infected by a range of infectious organisms with important, productivity, public health or economic consequences. Consequently, the potential role of wild pigs in outbreaks of important exotic diseases, like foot-and-mouth disease (FMD), has been a significant consideration in many countries. Disease modelling is one means to study the epidemiology of disease and has been used to assess the potential role of wild pigs in FMD incursions. Many of these models have been strategic in nature. They have contributed to a broad understanding of disease control in wild pigs (e.g. the concept of threshold densities and the need to cull pigs below this density for disease fadeout to occur), but have not incorporated many of the key drivers affecting disease behaviour. Some of these drivers include important ecological, behavioural and geospatial relationships, such as interaction between different host species and the distribution, density and connectivity of pig populations. New approaches to modelling disease spread such as spatial simulation models use spatial data and explicitly incorporate geospatial relationships. These approaches can provide useful quantitative models that can be used to explore mitigation strategies under specific disease outbreak conditions. However, to date, most studies have been limited by inadequate data, and computational issues or have not explored mitigation strategies. To inform management strategies for emergency epidemics such as FMD in wild pigs, there is scope to further develop and use models to explore a range of incursion scenarios and investigate the efficacy of different mitigation strategies.     

Characterization of Streptococcus uberis with special consideration of supposed pathogenicity factors]

Streptococcus uberis, as one of the principal causes of bovine streptococcal mastitis, has been characterized serologically and biochemically. Serological grouping of S. uberis revealed polysaccharide antigens of groups E, G, P and U. The biochemical properties of S. uberis, determined with the Strep-Zym identification system, differed clearly from those of S. agalactiae and S. dysgalactiae. Some cultures of S. uberis produced the enzymes hyaluronidase and neuraminidase. In addition S. uberis partly demonstrated CAMP-like synergistic hemolytic activities on sheep blood agar, reacted specifically with the lectins from Helix pomatia and Dolichos biflorus and produced bacteriocin-like inhibitors. This reactions, possibly of importance as virulence factors, as well as "DNA-fingerprinting" of S. uberis, might serve as individual markers of the respective cultures in epidemiological studies.     

Degenerative joint disease (osteoarthrosis): A review with special reference to the dog

Nomenclature, incidence, etiology, pathogenesis and morphological appearance of primary and secondary osteoarthrosis (osteoarthritis) are discussed. Differences and similarities between osteoarthrosis in man and the dog are mentioned. Primary osteoarthrosis occurs in the dog but secondary osteoarthrosis seems to be more frequent. In the dog hip dysplasia, Legg-Perthes' disease, osteochondritis dissecans of the shoulder and ununited anconeal process are conditions which, among others, give rise to osteoarthrosis. Changes in the knee caused by instability after rupture of the cruciate ligaments are not those of true osteoarthrosis. There is only minimal involvement of the joint cartilage in spite of osteophyte formation, thickening of the synovium and derangement of the menisci. Clinical signs in degenerative joint disease are usually insidious in onset. For a varying period of time they are as a rule not very conspicuous. In more advanced cases the cljnical manifestations are pain, limitation of movement and muscle atrophy. The underlying changes are cartilage destruction, subchondral sclerosis, osteophytes and thickening of the synovium. In very advanced cases in man there is even attrition of bone, which clinically leads to instability and subluxation. In human coxarthrosis cyst formations are frequently seen. Etiology and pathogenesis are obscure, or only partly understood, and in animals diagnosis is sometimes difficult. There is often poor correlation between severity of radiographic changes and clinical signs. Résumé. On examine la nomenclature, l'incidence, l'étiologie, la pathogénie et l'aspect morphologique de l'ostéo-arthrose (ostéo-arthrite) primaire et secondaire. On mentionne les différences et similitudes entre I'ostéo-arthrose rencontrée chez l'homme et chez le chien. L'ostéo-arthrose primaire se rencontre chez le chien, mais les cas d'ostéo-arthrose secondaire sont plus fréquents. Chez le chien, la dysplasie de la hanche, la maladie de Legg-Perthes, l'ostéochondrite disséquante de l'épaule et I'apophyse anconée disloquée sont des états qui, entre autres, engendrent l'ostéo-arthrose. Des transformations du genou, causées par une instabilité après rupture des ligaments croisés, ne sont pas celles de I'ostéo-arthrose proprement dite. Le rôle du cartilage articulaire n'est que minime, malgré l'apparition d'ostéophytes, l'épaississement des membranes synoviales et les troubles des ménisqua. Les signes cliniques des maladies articulaires dégéntratives sont généralement insidieux au départ. Pendant une période de temps variable, ils ne sont d'ordinaire pas très marqués. Pour les cas plus graves, les manifestations cliniques sont la douleur, la restriction des mouvements et l'atrophie musculaire. Les transformations qui sont à base de ces manifestations comprennent: destruction du cartilage, sclérose sous-cartilagineuse, ostéophytes et épaississement des membranes synoviales. Si chez l'homme, l'etat est très grave, on assiste même à l'attrition des os, qui, du point de vue clinique, mène à I'instabilité et la subluxation. En cas de coxarthrose chez l'homme, on observe fréquemment la formation de kystes. On ne connaît pas bien et ne comprend que partiellement l'étiologie et la pathogénie de ces maladies et, chez les animaux, le diagnostic est beaucoup plus difficile à établir. Très souvent on n'obtient pas de bonne corrélation entre I'importance des changements radiographiques et les signes cliniques. Zusammenfassung. Nomenklatur, Häufigkeit, Ätiologie, Pathogenese und morphologisches Aussehen von primärer und sekundärer Osteoarthrosis (Osteoarthritis) werden besprochen. Unterschiede und Ähnlichkeiten zwischen Osteoarthrosis des Menschen und des Hundes werden erwähnt. Primäre Osteoarthrosis tritt beim Hund auf, jedoch scheint die sekundäre Osteoarthrosis häufiger zu sein. Beim Hund sind Hüftendysplasie, Legg-Perthessche Krankheit, Osteochondritis dissecans der Schulter und unvereinigte anconeale Prozesse Zustände, die unter anderem zu Osteoarthrosis führen. Verändemngen am Knie, die durch Instabilität nach Ruptur der Kreuzbänder verursacht werden, sind nicht die echter Osteoarthrosis. Der Gelenkknorpel ist nur minimal betroffen, trotz Osteophytenbildung, Verdickung der Synovia und Meniskusverlagerung. Klinische Zeichen degenerativer Gelenkerkrankungen sind gewöhnlich anfangs mehrdeutig. In der Regel sind sie unterschiedlich lange nicht sehr auffällig. In fortgeschritteneren Fällen sind die klinischen Merkmale Schmerz, Bewegungsbehinderung und Muskelatrophie. Die zugrundeliegenden Veränderungen sind Knorpelzerstörung, subchondrale Sklerose, Osteophyten und eine Verdickung der Synovia. In sehr fortgeschrittenen Fällen beim Menschen tritt selbst Knochenabnutzung auf, die klinisch zu Instabilität und Subluxation führt. Bei Coxarthrosis des Menschen wird häufig Zystenbildung beobachtet. Ätiologie und Pathogenese sind dunkel oder nur teilweise aufgeklärt, und bei Tieren ist die Diagnose viel schwieriger. Oft besteht eine schlechte Korrelation zwischen der Schwere der radiographischen Verändemngen und den klinischen Zeichen.     

Risk factors for herdsman-reported foot-and-mouth disease in the Adamawa Province of Cameroon

We analysed responses from 147 Fulani herdsmen to a questionnaire about cattle herd-level risk factors for foot-and-mouth disease (FMD) in the previous year. The study used a cross-sectional design with a stratified, two-stage random sample of cattle herds in the Adamawa Province of Cameroon. The questionnaire was pre-tested at a local cattle market before a final version was translated into Foulfoulde (the local Fulani dialect). Variables were screened using a univariable analysis and logistic multiple-regression models were developed in a forward-selection process.

Fifty-eight percent (50–65; 90% CIs) of herdsmen reported FMD in their herd in the previous 12 months. Important risk factors for FMD in the previous 12 months included going on transhumance (OR = 2.6), buying cattle from markets (OR = 2.2), mixing of herds at watering points (OR = 2.4), feeding cotton-seed cake (OR = 3.3), buffalo near the herd (OR = 2.2) and administrative division. For the subset of herds that went on transhumance, coming in contact with an FMDV-diseased herd while on transhumance was the strongest factor (OR = 16).     

Identification of factors associated with increased excretion of foot-and-mouth disease virus

We investigated which variables possibly influence the amount of foot-and-mouth disease virus (FMDV) shed in secretions and excretions by FMDV infected animals, as it is likely that the amount of FMDV shed is related to transmission risk. First, in a separate analysis of laboratory data, we showed that the total amount of FMDV in secretions and excretions from infected animals is highly correlated with maximum titres of FMDV. Next, we collected data from 32 published scientific articles in which FMDV infection experiments were described. The maximum titres of FMDV reported in different secretions and excretions (the response variable) and the experimental conditions in which they occurred (the explanatory variables), were recorded in a database and analyzed using multivariate regression models with and without random effects. In both types of models, maximum titres of FMDV were significantly (p < 0.05) associated with types of secretions and excretions, animal species, stage of the disease and days post infection. These results can be used to prioritize biosecurity measures in contingency plans.     

Identification of geographic factors associated with early spread of foot-and-mouth disease

OBJECTIVE: To explore whether early analysis of spatial data may result in identification of variables associated with epidemic spread of foot and mouth disease. SAMPLE POPULATION: 37 farms with infected cattle (ie, case farms) reported within the first 6 days of the 2001 Uruguayan foot-and-mouth disease epidemic. PROCEDURE: A georeferenced database was created and retrospective analysis was performed on case farm location in relation to farm density, cattle density, farm type (ie, beef vs dairy cattle production), road density, case farm distance to the nearest road, farm size, farm ownership, and day of infection. Mean or median results of 1 to 3 day versus 4 to 6 day spatial data were compared. Spatial-temporal associations were investigated by correlation analysis. RESULTS: Comparison of mean or median values between the first 3 days and days 4 to 6 of the epidemic and results of correlation analysis indicated a significant increase in road density, cattle density, and dairy cattle production and a significant decrease in farm size and case farm distance to the nearest road that developed over time. A route that linked most case farms by the shortest possible distance and also considered significantly associated variables was created. It included 86.1% of all case farms reported by 60 days into the epidemic. CONCLUSIONS AND CLINICAL RELEVANCE: Epidemic direction can be assessed on the basis of road density and other spatial variables as early as 6 days into an epidemic. Epidemic control areas may be more effectively identified if local and regional georeferenced data are considered.     

Application of modelling to determine the absence of foot-and-mouth disease in the face of a suspected incursion

AIM: To use disease modelling to inform a response team about the number of animals per herd/flock to be examined, and the start date and duration of clinical surveillance required to be confident that foot-and-mouth disease (FMD) was not present on an island in New Zealand with a population of approximately 1,600 cattle, 10,000 sheep and a small number of pigs, goats and alpacas. METHODS: Because the probability of detecting clinical disease in (the) primary case(s) in larger herds and flocks was extremely low, deterministic and stochastic mathematical SLIR (susceptible, latent, infectious, recovered) models for the transmission of infection were constructed to estimate the date when clinical lesions in herds and flocks would be detected with 95% confidence. Surveillance targeted the first wave of infections following a suspect index case. RESULTS: If 70 cattle in herds of about 400 cattle were examined it was estimated it would take approximately 13 (90% stochastic range 9-19) days from first exposure before it would be possible to achieve 95% confidence for detecting clinical signs for a low-virulence virus, and 9 (7-14) days for a high-virulence virus. The duration of sufficiently accurate clinical detection was 17 (15-19) days and 13 (12-14) days for low- and high-virulence viruses, respectively. A sample of 70 sheep from flocks of >1,000 would be required to achieve clinical detection at about the same time but with a shorter period of detection than for cattle. The duration of effective detection could be increased by examining a larger sample in most sheep flocks, however the small size of many cattle herds in the study population limited the confidence of detecting group-level disease in cattle, therefore necessitating repeated herd inspections. The model suggested that group-level detection was not feasible if it was based on elevated body temperature alone because of short durations of fever in infected animals. CONCLUSION AND CLINICAL RELEVANCE: Simulation modelling is a useful and powerful tool for informing ongoing surveillance activities in the face of an exotic disease incursion. Results of modelling suggested to start clinical inspection activities at 4 days and to continue regular inspection twice a week for about 35 days after the date of first exposure, to satisfy the required 95% confidence threshold of clinical detection of FMD in cattle herds and sheep flocks.     

A capture-recapture analysis in a challenging environment: assessing the epidemiological situation of foot-and-mouth disease in Cambodia

We performed a two-source capture-recapture analysis for estimating the true number of villages that experienced clinical cases of foot-and-mouth disease (FMD) in 2009 in Svay Rieng province, Cambodia, and assessing the completeness of the official case-reporting procedure. As a first source, we used the 2009 official dataset made up of the 15 FMD-infected villages that were reported to the provincial authorities, and enlarged this list by assuming that all the villages located at less than 4 km from one of these villages also experienced clinical cases in 2009. In addition, we created a retrospective detection protocol using participatory tools cross-checked against a serological survey that detected 13 infected villages. The capture-recapture analysis of these two detection sources led us to the conclusion that 315 (CI(95%) 117-514) villages experienced clinical cases of foot-and-mouth disease in Svay Rieng province in 2009, corresponding to a village-level annual prevalence rate of 0.46 (CI(95%) 0.17-0.74). The official reporting rate to provincial authorities could therefore be evaluated at 0.05 (CI(95%) 0.03-0.13). An analysis of the sensitivity of the estimation of the number of cases to the radius used for enlargement of Source 1 was performed, indicating its low influence. This study clearly highlights the highly enzootic situation of Cambodia regarding foot-and-mouth disease and the substantial underreporting of clinically affected villages to veterinary authorities. We propose explanations for this low notification rate, stress the importance of accurate reporting procedures and, finally, discuss the potential of capture-recapture techniques as a tool for the quantitative evaluation of animal disease surveillance systems.     

A simple epidemiological method for animal trypanosomiasis to provide relevant data for effective financial decision-making

The epidemiology of bovine trypanosomiasis on Galana Ranch, Kenya was studied for one year (July 1980–June 1981), using measurements from an experimental population of 3 types of Boran cattle. The results were applied to the estimated ranch population at risk, and an attempt was made to measure the potential economic loss due to trypanosomiasis.

The potential losses in beef production due to trypanosomiasis in the ranch population at risk at Galana were estimated at around K.Shs. 8900/km², when the stocking rate was 14.2 Tropical Livestock Units per km². The estimated potential loss in the total population at risk was approximately K.Shs. 5 million (arround US$ 700 000 at 1981 values). These losses can be minimised by good management techniques based on accurate epidemiological information.

Results indicate that Orma-type Boran steers are more resistant to trypanosomiasis than Galana-type Boran steers. Although both types showed similar mortality rates, untreated Orma animals which survived showed a similar growth performance to animals maintained under 3-month Samorin prophylaxis. Untreated Galana Borans lost 14% of their body weight when compared with animals maintained under 3-month Samorin. Also, 305 of the untreated Orma Borans never showed typpanosomes in their blood over the study period, while all corresponding Galana Borans showed parasites; this resulted in a lower measured attact rate in Orma cattle.

In 1982, a combination of treating only those animals under trypanosome attack, relating the timing of chemotherapy to measured increased trypanosome attack, and the increased utilisation of the trypano-tolerant Orma Borans resulted in an annual saving of aroung US$ 110 000 in control costs and an increased land usage of approximately 5%.     

The 2001 epidemic of foot-and-mouth disease in the United Kingdom: epidemiological and meteorological case studies

The possibility of the airborne spread of foot-and-mouth disease during the 2001 epidemic in the uk has been investigated in three epidemiological case studies. On the basis of evidence from field investigations, and a simple meteorological analysis, it is concluded that the spread of disease was consistent with the airborne transport of virus. The distances ranged from less than 1 km to 16 km; six of the farms were over 6 km from the source and involved the passage of virus over the sea combined with meteorological conditions which strongly favoured airborne disease transmission. The results of detailed atmospheric modelling demonstrated that airborne virus could have challenged livestock on all the farms studied. However, with one exception the 24-hour average daily concentrations of the virus were significantly below the experimentally estimated threshold for infection. A detailed model intercomparison established that, under stable atmospheric conditions, peak concentrations of virus up to two orders of magnitude higher might have been experienced for short periods, owing to fluctuations within the plume of virus, and model limitations. This finding would significantly reduce the apparent discrepancy between the experimentally estimated threshold for infection and the modelling results.     

口蹄疫病毒感染与复制多元调控因素研究进展

口蹄疫(foot-and-mouth disease, FMD)是发生于偶蹄动物的一种急性高度传染性疫病,曾多次在世界范围内暴发流行。FMD致病原口蹄疫病毒(foot-and-mouth disease virus, FMDV)于感染后利用多种策略操纵宿主免疫机制和逃避抗病毒反应,以利于其感染复制。现对最近几年来影响调控FMDV感染与复制的多种因素从不同角度进行总结分析,以期为后续研究提供参考。     

Paratuberculosis with special reference to cattle. A review

Paratuberculosis is a chronic, granulomatous enteritis caused by Mycobacterium avium subspecies paratuberculosis affecting domestic and wild ruminants. The symptoms of clinical paratuberculosis are chronic diarrhoea and progressive weight loss while subclinically infected animals mainly have decreased production. The infection is widespread throughout the world and causes substantial financial losses for the farming industry. One of the major obstacles in the control of this disease, is the difficulty of identifying subclinically infected animals. This review gives a summary of several aspects of paratuberculosis including clinical importance, pathology, immunology and properties of the infectious agent. Special emphasis will be on the available diagnostic methods, their use and limitations.     

Predictive spatial modelling of alternative control strategies for the foot-and-mouth disease epidemic in Great Britain, 2001

A spatial simulation model of foot-and-mouth disease was used in March and early April 2001 to evaluate alternative control policies for the 2001 epidemic in Great Britain. Control policies were those in operation from March 20, 2001, and comprised a ban on all animal movements from February 23, 2001, and a stamping-out policy. Each simulation commenced with the known population of infected farms on April 10, 2001, and ran for 200 days. For the control policy which best approximated that actually implemented from late March, the model predicted an epidemic of approximately 1800 to 1900 affected farms, and estimated that the epidemic would be eradicated between July and October 2001, with a low probability of continuing beyond October 2001. This policy included the slaughter-out of infected farms within 24 hours, slaughter of about 1.3 of the surrounding farms per infected farm within a further 48 hours, and minimal interfarm movements of susceptible animals. Delays in the slaughter of animals on infected farms beyond 24 hours after diagnosis slightly increased the epidemic size, and failure to achieve pre-emptive slaughter on an adequate number of at-risk farms substantially increased the expected size of the epidemic. Vaccination of up to three of the most outbreak-dense areas carried out in conjunction with the adopted control policy reduced the predicted size of the epidemic by less than 100 farms. Vaccination of buffer zones (designed to apply available vaccine and manpower as effectively as possible) carried out in place of the adopted control policy allowed the disease to spread out of control, producing an epidemic involving over 6000 farms by October 2001, with no prospect of immediate eradication.