Effects of sustained control of brushtail possums on levels of Mycobacterium bovis infection in cattle and brushtail possum populations from Hohotaka, New Zealand

AIMS: To examine the effect of reducing the abundance of brushtail possums (Trichosurus vulpecula) on the distribution and prevalence of bovine tuberculosis (Mycobacterium bovis, Tb) in possums and the incidence of Tb in domestic cattle on a group of farms in the central North Island, New Zealand. METHODS: The cumulative yearly incidence of Tb infection from 12 cattle herds was estimated from annual tuberculin testing and abattoir inspection data over the period 1983-98. Intensive control of possum populations began for six of the herds in 1988, five herds in 1994 and the remaining herd in 1996. The prevalence and distribution of macroscopic M. bovis infection in possums and an index of possum abundance was estimated during yearly cross-sectional surveys from 1988 to 1998. This enabled formal testing of the link between the abundance of tuberculous possums and the incidence of Tb in cattle. RESULTS: Before possum control, infected possums were clustered in foci on or adjacent to the farms with the highest annual incidence of tuberculosis in cattle, and had an overall prevalence of macroscopic M. bovis infection of 2.3%. The prevalence of disease declined to zero with ongoing possum control, although infected possums continued to be found during the first 5 years of control. Maintaining the possum population at an average of 22.1% of its pre-control density significantly reduced the odds of the cumulative yearly incidence of Tb in cattle by 77% during the first 5 years of possum control and a further 65% in the second 5-year period. Nine of 11 tuberculous possums identified since the start of possum control were found within the areas where infected possums were clustered during the pre-control survey, suggesting that the persistence of infection within these clusters rather than infected immigrants was the source of ongoing disease. Annual estimates of the prevalence of tuberculous possums broadly followed the predictions of Barlow's possum-Tb model for a controlled possum population. CONCLUSION: The results support the hypothesis that tuberculous possums transmit bovine tuberculosis to domestic cattle, and therefore that reducing the abundance of tuberculous possums reduces the incidence of Tb in cattle. If the level of possum culling is sufficient, it appears that M. bovis infection may be eradicated from possum populations. Better information on population density, rate of increase and annual culling rates would have been needed for a truly independent examination of the Barlow possum-Tb model.     

Trends and advances in the diagnosis and control of paratuberculosis in domestic livestock

Paratuberculosis (pTB) is a chronic granulomatous enteritis caused by Mycobacterium avium subsp. paratuberculosis (MAP) in a wide variety of domestic and wild animals. Control of pTB is difficult due to the lack of sensitive, efficacious and cost-effective diagnostics and marker vaccines. Microscopy, culture, and PCR have been used for the screening of MAP infection in animals for quite a long time. Besides, giving variable sensitivity and specificity, these tests have not been considered ideal for large-scale screening of domestic livestock. Serological tests like ELISA easily detects anti-MAP antibodies. However, it cannot differentiate between the vaccinated and infected animals. Nanotechnology-based diagnostic tests are underway to improve the sensitivity and specificity. Newer generation diagnostic tests based on recombinant MAP secretory proteins would open new paradigm for the differentiation between infected and vaccinated animals and for early detection of the infection. Due to higher seroreactivity of secretory proteins vis-à-vis cellular proteins, the secretory proteins may be used as marker vaccine, which may aid in the control of pTB infection in animals. Secretory proteins can be potentially used to develop future diagnostics, surveillance and monitoring of the disease progression in animals and the marker vaccine for the control and eradication of pTB.     

The effect of fertility control on the transmission of bovine tuberculosis in wild brushtail possums

AIM: To determine the effect of fertility control on the rate of transmission of bovine tuberculosis (Tb), caused by Mycobacterium bovis, in brushtail possums (Trichosurus vulpecula). METHODS: At two study sites with a history of Tb infection in the resident possum population, a sample of adult male and female possums (n=50), determined by palpation to be Tb-free, was surgically sterilised by gonadectomy. A sample of untreated Tb-free male and female possums (n=54) served as controls. Each study site was trapped every 2 months over a 3-year period, and the Tb status of the individuals in the trial assessed. At the conclusion of the trial, all remaining experimental individuals were killed, necropsied and examined for characteristic lesions typical of Tb. The rate of transmission of Tb infection was estimated using the incidence of tuberculous cases in the experimental animals and comparing it between sites, sex and sterilisation treatment. RESULTS: Sterilisation by gonadectomy resulted in a reduction in the rate of transmission of Tb in male possums by 53%, but a corresponding increase in sterilised females for reasons that are still unclear. However, this interaction was statistically weak (p=0.10). When the sexes were combined, there was no overall effect of sterilisation on the rate of transmission of Tb (p=0.43). Sterility treatment notwithstanding, there was a highly significant difference in the rate of transmission between the sexes (p=0.01), being almost one order of magnitude higher in untreated males compared with untreated females. CONCLUSIONS: Although lacking strong statistical support, these results suggest that fertility control that targets endocrine control of fertility may provide some additional benefits for disease control over that achieved by reductions in population density, by reducing the rate of transmission of M. bovis in male possums. However, additional studies are needed to confirm the validity of these results. The large difference in the rate of transmission of M. bovis in untreated males compared with untreated females suggests that transmission of Tb among males may be an important driver of the dynamics of Tb infection in possums.     

Bovine tuberculosis in a possum from the Orongorongo Valley, Wellington

The first confirmed case of a tubercular possum in the Orongorongo Valley forest is reported from a population intensively studied for 20 years. The victim was a five-year-old male recaptured 20 times over 3% years. Its annual home range was about 1.8 hectares but this dropped to 0.4 ha during its last year of life. Its range overlapped with at least 15 others. The animal appeared normal and healthy in July 1985 but died of advanced, generalised bovine tuberculosis 12 weeks later. The nearest confirmed cases of tubercular possums were reported 1.3 km away in 1976 and 4 km away in 1979. The Orongorongo possum was unlikely to have contacted any cattle for over three years. The infection was probably transmitted from the Wainuiomata Valley by possums or pigs. The Orongorongo River was no barrier to the spread of the infection. Although most of the neighbouring possums were trapped and examined several times over the following year, no tubercular animals were detected.     

Behavioural studies on the potential for direct transmission of tuberculosis from feral ferrets (Mustela furo) and possums (Trichosurus vulpecula) to farmed livestock

Studies were conducted to evaluate the response of cattle and deer to ferrets which were sedated so they behaved like terminally tuberculous animals, and to compare this with the response of cattle, deer and sheep to sedated possums. Six groups of deer and two groups of cattle were exposed to a sedated ferret and to a sedated possum. Both livestock species showed interest in the possum by sniffing and licking it, but they only briefly touched the ferret and no licking or extended investigation was observed. The proportion of available time spent in physical contact with the possum by cattle was 7.7 times as high as for the ferret, and for the deer was 5.7 times as high. The behavioural response of three groups of sheep to a sedated possum was investigated, and sheep showed limited interest beyond viewing the possum from a distance. The amount of time spent by sheep investigating the possum was very low and the intensity of exploration was also low. For possums, at least one deer was within 1.5 m (an estimate of the distance that tuberculosis can be transmitted by aerosol) for 50.9% of observation time, and in physical contact with the possum for 9.5% of time. The figures for cattle were 69.3% and 17.3%, while those for sheep were 6.9% and 0.3%. In interactions with ferrets, the equivalent figures were 29.8% within 1.5 m and 2.2% in physical contact for cattle, and 20.8% and 1.1% for deer. Tuberculous possums commonly and tuberculous ferrets less commonly have lung lesions and/or discharging sinuses, and may excrete Mycobacterium bovis intermittently or continuously in aerosols or discharges. The exploratory behaviour of deer and cattle in this study would provide opportunities for them to become infected with M. bovis if they had contact with infectious possums, and less probably with ferrets. The response of sheep to possums suggests that they would be much less likely to contract the disease.     

IgE and IgG antibodies to flea antigen in differing dog populations

A radioimmunoassay was developed for the detection of IgG and IgE canine antibodies against partially purified flea antigen. Low background levels were found in flea naive dogs, but high levels of both IgE and IgG antibodies were found in many sera from dogs with clinical flea hypersensitivity. In sera from non-allergic dogs exposed chronically to fleas, IgE levels differed little from background, and levels of IgG anti-flea antibodies were much lower than those from the flea allergic group. The results suggest that chronic flea exposure may result in partial or complete tolerance rather than hyposensitization in the commonly accepted sense.     

A behaviour study on the potential for direct transmission of tuberculosis from possums (Trichosura vulpecula) to alpacas (Lama pacos), and the converse from alpacas to possums

Aims. To evaluate the potential for the direct transmission of tuberculosis from possums to alpacas, and vice versa.

Methods. A field study was conducted on an alpaca farm in Northland, New Zealand on 7 January 1999. Observations were recorded on the interaction of one group of male alpacas with a simulated dead possum, one male and one female alpaca group with a simulated terminally tuberculous possum, and one group of male alpacas with a normal possum in an enclosure from which the animals could not escape. The possum was sedated with ketamine as hydrochloride to simulate death (inactive; no movement), and terminal illness (active, into-ordinated movement around the paddock). The observations were based on the focal animal sampling technique, they were un-replicated, and recorded visually and manually with intermittent still photography.

Results. Both male and female alpacas showed strongly inquisitive interaction with the possum. They clustered around the possum (focal animal) very soon after it was observed by the first member of the group. The interest of the majority of both sex groups remained high for the observation periods of approximately 30 minutes, and most individuals remained within 5 metres of the possum for that time. Approximately 50% of the alpacas were within possible aerosol transmission distance of 2 metres from the sedated, erratically mobile possum with their heads towards it for approximately 50% of the two observation periods. Aggressive behaviour was recorded for a young male with stamping on the moving possum. Similar, but more vigorous and prolonged stamping behaviour was recorded for a female with a young (<1 week) offspring (cria).The stamping behaviour was accompanied by very close nose to nose contact of the alpaca and possum. At one point the female threw the possum approximately 1.5 metres in the air with her teeth. The group of male alpacas placed in an enclosure with an unsedated normal possum generally moved away from the possum during its rapid active attempts to escape. When it became inactive their approaches were cautious and only once elicited a defence reaction from the possum, from which they recoiled. One male made one attempt to stamp on the active possum. Soon after the possum became inactive in a small loose hay pile, the alpacas lost interest in it.

Conclusions. The alpaca / possum behavioural interactions show there is potential for direct aerosol transmission of tuberculosis from possums to alpacas, but probably not from alpacas to possums.     

Risk factors associated with bovine tuberculosis in traditional cattle of the livestock/wildlife interface areas in the Kafue basin of Zambia

We conducted a cross-sectional study from August 2003 to February 2004 to identify risk factors for bovine tuberculosis (BTB) in the Kafue basin of Zambia. We investigated a total of 106 herds of cattle for presence of BTB using the comparative intradermal tuberculin test (CITT) while an interviewer-administered questionnaire was used to gather epidemiological data on herd structure, management and grazing strategies. BTB prevalence at herd level was estimated and possible risk factors were investigated using the multiple logistic regression model. The true herd level prevalence of BTB was estimated at 49.8% (95% CI: 37.9, 61.7%). The logistic regression model showed that cattle herd BTB status was highly associated with area and husbandry practices. When compared to Kazungula, cattle herds in Blue Lagoon were more likely to test positive for BTB when other factors such as management practices were controlled (OR=10.5). In terms of grazing strategies, transhumant herds (TH) had higher odds (OR=3.0) of being positive compared to sedentary herds (OR=1.0). The results in this study provide preliminary information about potential risk factors that were found to be associated with BTB status in cattle.     

羊草生长和光合生理特性对不同施磷强度的响应

为探索羊草(Leymus chinensis)生长特征和光合生理参数对磷添加的响应,本研究通过盆栽试验设置4个施磷水平(0、70、140、210?kg·hm?2),分析不同施磷强度对羊草生长和光合生理特性的影响.结果表明:1)施磷量在70～210?kg·hm?2范围内对羊草株高和生物量的积累均有促进作用,并且在140?kg·hm?2时促进效果最明显.2)羊草光合作用对土壤施磷强度的响应不同,随着施磷强度的升高,净光合速率呈先增加后降低的趋势;叶绿素荧光在施磷强度为70～140?kg·hm?2范围内最大光化学效率(Fv?/?Fm)、PSⅡ活性、初始荧光(Fo)出现最大值,而Fo?/?Fm出现最小值.拟合方程分析表明,施磷强度在148.75?kg·hm?2时更加有利于羊草生物量的积累.     

Prevalence and spatial distribution of bovine tuberculosis in brushtail possums on a forest-scrub margin

Tuberculosis caused by Mycobacterium bovis was diagnosed in 36 of 68 (53%) brushtail possums (Trichosurus vulpecula) trapped in August 1992 from a population of exceptionally low density (trap catch <3%) on a forest-scrub margin in Westland, New Zealand. The prevalence of tuberculosis in possums, based solely on gross lesions, was at least twice that previously recorded in New Zealand, and was about seven times that recorded from the same population in 1980. More male (66%) than female (33%) possums had grossly visible tuberculous lesions. The distribution of infection appeared continuous along the forest-scrub margin. Both stoats (Mustela erminea) and one of six hares (Lepus europaeus occidentalis) trapped were also infected with M. bovis.     

Screening food-borne and zoonotic pathogens associated with livestock practices in the Sumapaz region,Cundinamarca, Colombia

Hazardous practices regarding antibiotics misuse, unsanitary milking procedures, and the commercial sales of raw milk and unpasteurized dairy products are currently being practiced by livestock farmers in the Sumapaz region (Colombia). The purpose of this study was to screen for food-borne and zoonotic pathogens associated with local livestock practices. We evaluated 1098 cows from 46 livestock farms in the Sumapaz region that were selected by random. Of the total population of cattle, 962 animals (88%) were tested for bovine TB using a caudal-fold tuberculin test and 546 (50%) for brucellosis by a competitive ELISA. In the population tested, 23 cows were positive for Brucella sp. representing a 4.2% seroprevalence and no cases of bovine tuberculosis were found. In addition, food-borne contamination with Escherichia coli and Staphylococcus aureus was assessed together with antibiotic susceptibility for ten different antibiotics in milk samples from 16 livestock farms. We found that 12 of the farms (75%) were contaminated with these food-borne pathogens. Noteworthy, all of the isolated pathogenic strains were resistant to multiple antibiotics, primarily to oxytetracycline and erythromycin. Our findings suggest that livestock products could be a source of exposure to Brucella and multidrug-resistant E. coli and S. aureus strains as a result of unhygienic livestock practices in the Sumapaz region. Training in good farming practices is the key to improving safety in food production.     

Veterinarian injuries associated with bovine TB testing livestock in Michigan, 2001

Testing all the cattle in an entire state with a uniform procedure for each animal affords an opportunity to relate human injury data to a known number of animals handled while carrying out a standardized procedure. Our objective was to describe the type and incidence density of injuries associated with TB-testing a large number of cattle herds, and to delineate the various factors associated with the risk of injury. A survey was mailed to all veterinarians (N = 259) who had completed at least five official bovine TB (bTB) herd tests in Michigan in 2001. We collected data regarding basic demographics and health status, work experience, veterinary specialty, and practice information. Each veterinarian was also requested to complete a separate injury questionnaire for each injury received while TB testing livestock in 2001. Accurate addresses were found for 247 eligible veterinarians, 175 (71%) of whom returned the survey. Thirty-six veterinarians reported a total of 53 injuries (10 major, 12 minor and 31 self-treated). Hands (29%) and legs (21%) were the anatomic locations most frequently injured, with sprains/strains (30%) and abrasion/contusion (30%) the most common types of injuries sustained. The overall incidence density of injuries was 1.9 per 10,000 animals tested. Female gender (RR = 3.3), being employed by the government (RR = 4.5), and smoking (RR = 6.0) were significantly associated with a higher rate of injury. Significant colliniearities were found between some risk factors associated with an increased rate of injury and participants thought 81% of their injuries could have been prevented. These results are explained by the administrative structure of the bTB testing program in Michigan, and the changing demographics of the veterinary workforce.     

Temporal patterns in bovine tuberculosis in a brushtail possum population contiguous with infected cattle in the Ahaura Valley, Westland

AIMS: To determine temporal and spatial patterns of bovine tuberculosis (Tb) in a population of brushtail possums (Trichosurus vulpecula) free from commercial and recreational hunting and living contiguously with livestock, and to relate these patterns to measures of possum health and density. METHODS: Possums were trapped on 11 lines located on a forest-rough grazing margin in the Ahaura Valley in Westland in 1979-80 and each August from 1992 to 1996, and were examined post mortem for gross lesions indicative of Tb. Infection levels in possums were compared with Th test data from cattle grazing in the same area. RESULTS: Tuberculosis was identified from the trapped sample of possums in 1980. Trapping of further possums on the same trap lines confirmed the presence of the disease each year from 1992 to 1996, and suggested a clustering of infection in time and space. The prevalence of Tb in possums declined with increasing possum population size and well being, and decreasing age. The prevalence of Tb in possums was highest in 1980 and 1992, and appeared to roughly coincide with similar upsurges in Tb in nearby cattle. CONCLUSIONS: Our results suggest that the exceptional levels of Tb recorded in possums in 1992 had a direct effect on possum numbers, and gave rise to very low trap catches in 1993-94. They also suggest that Tb can persist for several years in possum populations existing well below the 5% trap catch targeted by regional councils for Tb possum control.     

酸化剂在畜禽业中的应用研究进展

饲料中长期添加抗生素不仅会造成畜产品药物残留，危害人体健康，而且会影响畜区生态平衡和环境卫生。在许多国家和地区，包括欧盟成员国、日本、美国、澳大利亚等，允许在饲料中添加的抗生素种类越来越少，但是停用抗生素不可避免的会影响畜禽的健康，寻找抗生素替代品成为目前研究的热点。本文主要介绍一下抗生素替代品一酸化剂在畜禽业中的应用。     

Mortality rate and movements of brushtail possums with clinical tuberculosis (Mycobacterium bovis) infection

AIM: To describe the mortality rate and movements of brushtail possums (Trichosurus vulpecula) with clinical tuberculosis (Mycobacterium bovis) from a site in native podocarp/hardwood forest, in the Orongorongo Valley, Wellington. METHODS: Possums with clinical tuberculosis (Tb) were identified through routine trapping on live capture grids and were fitted with radio-collars, and located at approximately monthly intervals for 2.5 years. The survival times of radio-collared tuberculous and non-diseased possums were used to estimate the instantaneous additional mortality rate due to clinical Tb. The spatial behaviour of clinically tuberculous possums was compared with that of non-diseased possums, using both den and trap locations. The frequency of long-distance movements of both tuberculous and non-diseased possums was also determined. A possum was defined as having undertaken along-distance movement when it moved at least 200 m from the centre of its activity range and then returned to its established activity range or died. RESULTS: The mean survival time of clinically tuberculous possums was 4.7 (SE 0.79) months. The instantaneous additional mortality rate due to clinical Tb was estimated to be between 1.08 year-1 and 2.38 year-1, with the lower figure including an unknown portion of the incubation period in the estimate. Estimates of denning and activity ranges of tuberculous possums were approximately 22-30% larger, on average, than the ranges of non-diseased possums, but the differences were not significant. Both tuberculous and non-diseased possums undertook long-distance movements up to 700 m from the centre of their activity range. However, the majority of tuberculous possums died within or near their established activity range. CONCLUSIONS: This study estimated the mortality rate during the clinical stages of Tb and, as such, did not represent a true estimate of the disease-induced mortality rate (alpha) used in most epidemiological models of possums and Tb. However, the lower estimate of the additional mortality rate due to clinical disease could be considered an approximation to alpha. The movement patterns of clinically tuberculous possums were, overall, not substantially different from non-diseased possums. The occurrence of long-distance movements by tuberculous possums sometimes coincided with the advanced stage of clinical disease. However, the majority of tuberculous possums died within their established activity area. Long-distance movements by resident possums during the terminal stages of disease represent a direct risk for transmission of Tb to livestock on farms within approximately 1 km of infected possum populations.     

Global perspectives on nematode parasite control in ruminant livestock: the need to adopt alternatives to chemotherapy,with emphasis on biological control

Effective, sustainable control of nematode parasites of grazing livestock is becoming evermore challenging and difficult. This is largely due to two contrasting issues. One is the rapid escalation of resistance to anthelmintic drugs, which is arguably the greatest problem now facing the small ruminant industries worldwide. Secondly, there is the increasing trend towards organic farming, in which there is prohibition of the prophylactic use of all chemical compounds. Livestock producers urgently need non-chemotherapeutic alternatives in parasite control. Researchers have responded to this challenge and a variety of quite different approaches have been the subject of intense investigation in many countries for several decades now. These vary in relation to their stage of development for on-farm use, their utility, and their applicability across the spectrum of grazing livestock enterprises throughout the world. One relatively recent innovation is the biological control approach to nematode parasites. This has now reached the stage of commercialization. This review focuses on these issues and provides an overview of the possible ways in which the biological control of nematode parasites could be employed in grazing ruminant livestock systems worldwide.     

Toxicology of oil field wastes. Hazards to livestock associated with the petroleum industry

In oil-producing states, the proximity of livestock to drilling operations and production sites often results in poisoning of animals from ingestion of crude oil, condensate, salt water, heavy metals, and caustic chemicals. The heavy metals encountered most frequently are lead from pipe joint compound and arsenicals and chromates used as corrosion inhibitors. Numerous toxic and caustic chemicals are used in drilling muds and fluids. Crude oil and salt water spills are common occurrences around production sites. Pipeline breaks may result in exposure of livestock to crude oil or refined petroleum hydrocarbons. Ingestion of petroleum hydrocarbons may result in sudden death from peracute bloat. The most common cause of illness or death following exposure to petroleum hydrocarbons is aspiration pneumonia, which may cause a chronic progressive deterioration of health, with death after several days or weeks. Cases in which livestock are exposed to oil, salt water, or caustic chemicals, but do not die acutely or from aspiration pneumonia are more frustrating to diagnose. In these cases, parasitism, poor nutrition, and other debilitating diseases must be considered. Anorexia, weight loss, and decreased rumen motility may be caused by a disruption of normal rumen function. Petroleum hydrocarbons, salt water, and caustic chemicals have the potential of altering rumen flora and enzymatic processes as well as damaging the ruminal and gastrointestinal epithelium. The toxicity of petroleum hydrocarbons appears to be related more closely to the volatility and viscosity of the product than to other factors. The more volatile straight chain and aromatic petroleum hydrocarbons have a greater potential for aspiration pneumonia and may produce an anesthetic-like action if absorbed systemically. The more volatile petroleum hydrocarbons also are more irritating to skin and mucous membranes and appear to be more damaging to rumen flora. Treatment of petroleum hydrocarbon ingestion is aimed at preventing aspiration pneumonia and the animal's absorption of highly volatile components. Activated charcoal slurries and, in some instances, vegetable oil may be used to absorb the ingested petroleum or alter its viscosity to minimize absorption and aspiration. These procedures should be followed by the administration of rumenatories or saline cathartics to hasten the evacuation of the gastrointestinal tract. Chronic poor performance animals with anorexia and rumen dysfunction may respond to fresh rumen inoculant, intravenous glucose, and B-complex vitamins. Prognosis primarily hinges on whether or not aspiration pneumonia has occurred. Treatment of aspiration pneumonia rarely is effe     

Low prevalence of bovine tuberculosis in Somali pastoral livestock, southeast Ethiopia

A cross-sectional study of bovine tuberculosis (BTB) detected by the comparative intradermal tuberculin test (CIDT) was conducted in livestock of the Somali region in southeast Ethiopia??in four pastoral associations from January to August 2009. In 94 herds, each of 15 cattle, camels, and goats was tested per herd leading to a total of 1,418 CIDT tested animals, with 421 cattle, 479 camels, and 518 goats. A herd was considered positive if it had at least one reactor. Prevalence per animal species was calculated using a xtgee model for each species. The individual animal prevalence was 2.0% [95% confidence interval (CI), 0.5?C8.4], 0.4% (95% CI, 0.1?C3%), and 0.2% (95% CI, 0.03?C1.3) in cattle, camels, and goats, respectively. Prevalence of avian mycobacterium purified protein derivative (PPD) reactors in cattle, camels, and goats was 0.7% (95% CI, 0.2?C2.0%), 10.0% (95% CI, 7.0?C14.0%), and 1.9 (95% CI, 0.9?C4.0%), respectively, whereby camels had an odds ratio of 16.5 (95% CI, 5.0?C55.0) when compared to cattle. There was no significant difference between livestock species in BTB positivity. In the present study, the prevalence of bovine tuberculosis was low in Somali pastoral livestock in general and in camels and goats in particular. The high proportion of camel reactors to avian PPD needs further investigation of its impact on camel production.