Internal parasites of possums (Trichosurus vulpecula) from Kawau Island, Chatham Island and Stewart Island

As part of a search for pathogens that might be useful agents for biological control of possums, the three largest offshore islands of New Zealand that still have possums were surveyed to determine the pathogens present in these isolated populations. Brushtail possums from Kawau Island (n = 158), Chatham Island (n = 214) and Stewart Island (n = 194) were examined for internal parasites. Possums from Kawau Island were infected with Eimeria spp. (16.7%), Bertiella trichosuri (5.2%) and Purustrongyloides trichosuri (15.5%). No Paraustrostrongylus trichosuri or Trichostrongylus spp. were found. Possums from Chatham Island were infected with Eimeria spp. (10.9%). Bertiella trichosuri (3.6%), T colubriformis (6.6%), T retortaeformis (1%) and T. vitrinus (0.5%). No Parastrongyloides or Paraustrostrongylus spp. were found. Possums from Stewart Island were infected only with Eimeria spp. (4.6%). Because of their paucity of some parasites, the opportunity exists to use these offshore islands to study the introduction and spread of a parasite into a possum population, and what technology would be required to bring it to hyperendemicity.     

Internal parasites of possums (Trichosurus vulpecula) from Kawau Island,Chatham Island and Stewart Island

As part of a search for pathogens that might be useful agents for biological control of possums, the three largest offshore islands of New Zealand that still have possums were surveyed to determine the pathogens present in these isolated populations. Brushtail possums from Kawau Island (n = 158), Chatham Island (n = 214) and Stewart Island (n = 194) were examined for internal parasites.

Possums from Kawau Island were infected with Eimeria spp. (16.7%), Bertiella trichosuri (5.2%) and Parastrongyloides trichosuri (15.5%). No Paraustrostrongylus trichosuri or Trichostrongylus spp. were found. Possums from Chatham Island were infected with Eimeria spp. (10.9%). Bertiella trichosuri (3.6%), T. colubriformis (6.6%), T. retortaeformis (1%) and T. vitrinus (0.5%). No Parastrongyloides or Paraustrostrongylus spp. were found. Possums from Stewart Island were infected only with Eimeria spp. (4.6%).

Because of their paucity of some parasites, the opportunity exists to use these offshore islands to study the introduction and spread of a parasite into a possum population, and what technology would be required to bring it to hyperendemicity.     

Endoparasites of brushtail possums (Trichosurus vulpecula) from the South Island,New Zealand

As part of a study to assess whether endoparasites could assist in the biological control of brushtail possums in New Zealand, we investigated the composition and distribution of possum endoparasites in the South Island. Possums were collected near five of the original release areas in the South Island: Banks Peninsula, Hokitika, Nelson, Dunedin and Invercargill.

Among the nematodes, those most frequently encountered were Trichostrongylus spp., which were present in possums from all five study areas. Trichostrongylus species from possums in the Invercargill area comprised 4.5% T. colubriformis, 0.9% T. vitrinus and 11.3% T. retortaeformis. Paraustrostrongylus trichosuri and Parastrongyloides trichosuri were found only in the Invercargill area, where they infected 1.4% and 14% of possums respectively. The cestode Bertiella trichosuri was present in possums from all locations except Dunedin. The protozoan Eimeria spp. occurred in all areas.

These are the first records of Parastrongyloides trichosuri, Paraustrostrongylus trichosuri, T. vitrinus, T. retortaeformis and Eimeria spp. in South Island possums.

The prevalence of endoparasites and the intensity of infection was very low compared to the lower North Island of New Zealand. Endoparasites at the existing levels in the South Island probably have very little effect on possum populations.     

Endoparasites of brushtail possums (Trichosurus vulpecula) from the South Island, New Zealand

As part of a study to assess whether endoparasites could assist in the biological control of brushtail possums in New Zealand, we investigated the composition and distribution of possum endoparasites in the South Island. Possums were collected near five of the original release areas in the South Island : Banks Peninsula, Hokitika, Nelson, Dunedin and Invercargill. Among the nematodes, those most frequently encountered were Trichostrongylus spp., which were present in possums from all five study areas. Trichostrongylus species from possums in the Invercargill area comprised 4.5% T. colubriformis, 0.9% T. vitrinus and 11.3% T. retortaeformis. Paraustrostnmgylus trichosuri and Parastrongyloides trichosuri were found only in the Invercargill area, where they infected 1.4% and 14% of possums respectively. The cestode Bertiella trichosuri was present in possums from all locations except Dunedin. The protozoan Eimeria spp. occurred in all areas. These are the first records of Parastrongyloides trichosuri, Paraustrostrongylus trichosuri, T. vitrinus, T. retortaeformis and Eimeria spp. in South Island possums. The prevalence of endoparasites and the intensity of infection was very low compared to the lower North Island of New Zealand. Endoparasites at the existing levels in the South Island probably have very little effect on possum populations.     

Resolution of Mycobacterium bovis infection in wild brushtail possums (Trichosurus vulpecula)

The brushtail possum (Trichosurus vulpecula) is the principal wildlife reservoir of Mycobacterium bovis in New Zealand (Morris and Pfeiffer 1995). Tuberculosis in possums is a progressive, fatal infection. The complete resolution of infection in possums has not been reported. The purpose of this communication is to present two cases of complete and spontaneous resolution of tuberculosis in wild, naturally infected possums. During an 11-year (1989-2000) longitudinal study of a possum population at Castlepoint in the Wairarapa, 90 bacteriologically-confirmed cases of M. bovis infection were observed, and 88 of the tuberculous possums were either found dead or were presumed to have died when they ceased to be trapped. As the home range of adult possums is stable (Efford et al 2000) it was assumed that if an adult possum could no longer be trapped, it had died. In many cases, the declining physical condition of a tuberculous possum prior to its disappearance supported the assumption. However, two cases survived and were euthanised, one 15 months and the other 30 months after they first showed clinical signs of infection. When examined post mortem, neither showed evidence of M. bovis infection. The case histories are described and the significance of the observations discussed.     

Lung worm (Marsupostrongylus spp.) infection in common brushtail possums (Trichosurus vulpecula)

Marsupostrongylus spp. are the metastrongyloid nematodes most commonly associated with verminous pneumonia in Australian marsupials. Currently, there is a scarcity of information regarding this parasite in the common brushtail possum (Trichosurus vulpecula). Thirty-four free-living possums submitted to two wildlife hospitals in Sydney, Australia, between 2008 and 2015 were diagnosed with verminous pneumonia on postmortem examination. The majority of possums presented ill with multiple comorbidities. However, only five cases had clinical signs of respiratory disease. Necropsy and histopathology revealed extensive lung lesions characterised by diffuse, mixed interstitial infiltrates of macrophages, lymphocytes and plasma cells with mild to marked concentrations of eosinophils. Bronchopneumonia, pulmonary oedema, interstitial fibrosis, atelectasis and type II pneumocyte hyperplasia were also present in most cases. Adult nematodes, first-stage larvae and embryonating eggs were present in the large airways and alveolar spaces. The parasites were definitively identified as Marsupostrongylus spp. in eight cases with presumptive diagnoses based on histopathological characteristics reached in a further 26 cases. Twenty-nine of the 34 affected possums were adults with no sex predisposition. A review of the brushtail possum records at Taronga Wildlife Hospital from 1999 to 2015 revealed no lungworm infections were reported in the 45 possums examined before 2008. However, between 2008 and 2015, 30 of 47 possums (63.8%) examined were diagnosed with metastrongyloid lungworms. This case series is the first detailed report of Marsupostrongylus nematodes in common brushtail possums and highlights the clinical and pathological features, along with epidemiological findings.     

Natural transmission of Mycobacterium bovis infection in captive brushtail possums (Trichosurus vulpecula)

AIMS: To examine natural transmission of bovine tuberculosis (Mycobacterium bovis infection) in captive brushtail possums (Trichosurus vulpecula) and to determine if this mode of transmission could be employed to challenge possums in vaccination studies. METHODS: Three experiments were conducted. In Experiment 1, 11 pairs of possums were housed together in cages, one of the pair having been experimentally infected with M. bovis. Of the in-contact possums 5/11 had been vaccinated with bacille Calmette-Guerin (BCG). In Experiment 2, three susceptible possums were placed in a colony of 19 possums that had been experimentally infected with M. bovis. In Experiment 3, the four most socially active possums in each of two colonies (24 possums in one colony and 23 in the other) were experimentally infected with M. bovis, and 10 of the remaining possums in each colony were vaccinated with BCG. RESULTS: In Experiment 1, transmission of M. bovis infection occurred in only 1/11 pairs. In Experiment 2, none of the three in-contact possums became infected. In Experiment 3, infection was transmitted to 5/20 in-contact possums in one colony and 12/19 in-contact possums in the other. The possums that became infected by natural transmission were significantly more socially interactive than those that remained free of infection (p<0.05). CONCLUSIONS: When susceptible and infected possums were randomly mixed, the rate of transmission of M. bovis was low, but when highly sociable possums were infected the rate of transmission increased markedly. The risk of transmission was dependent on the close proximity of infected and susceptible possums and the frequency and duration of their social interactions. Natural transmission from experimentally infected to incontact possums in a colony would be a useful way of studying the pathogenesis of tuberculosis in this species, and the social behaviour of the possums studied should be taken into account. The high degree of variation in the rate of natural transmission of M. bovis infection between possums makes this mode of transmission unreliable for assessing vaccine efficacy.     

The pathogenesis of experimental endo-bronchial Mycobacterium bovis infection in brushtail possums (Trichosurus vulpecula)

AIM: To study the nature and development of experimentally induced respiratory tuberculosis in possums and compare the lesions observed with those seen in the natural disease. METHODS: Thirty-three adult possums were inoculated via the endo-bronchial route with 20-100 colony forming units of Mycobacterium bovis. The possums were killed at 1,2,3 and 4 weeks after inoculation and the nature and distribution of the lesions studied in detail histopathologically. Alveolar macrophages recovered from the infected possums were also studied ultrastructurally. RESULTS: Macroscopic lesions were largely confined to the respiratory tract, increasing in size and number with time. Histology greatly increased the detection of the total number of lesions. The most common sites affected outside the respiratory tract were the liver and hepatic lymph nodes, but lesions were less common in peripheral lymph nodes than is observed in the natural disease. Intra-pulmonary lesions were centred on blood vessels and their associated lymphatics. Peripheral blood lymphocyte blastogenic responses to M. bovis antigens were first detected at 3 weeks after inoculation, which was 1 week after lymphocyte infiltrations were detected in the lungs, but 1 week before the majority of infections became generalised. CONCLUSIONS: Differences in the nature of pulmonary lesions and the distribution of lesions were observed between experimentally induced and the natural disease. Rapid haematogenous and lymphatic spread occurs early in the experimentally induced disease.     

The pathogenesis of experimental endo-bronchial Mycobacterium bovis infection in brushtail possums (Trichosurus vulpecula)

Aim. To study the nature and development of experimentally induced respiratory tuberculosis in possums and compare the lesions observed with those seen in the natural disease.

Methods. Thirty-three adult possums were inoculated via the endo-bronchial route with 20–100 colony forming units of Mycobacterium bovis. The possums were killed at 1, 2, 3 and 4 weeks after inoculation and the nature and distribution of the lesions studied in detail histopatbologically. Alveolar macrophages recovered from the infected possums were also studied ultrastructurally.

Results. Macroscopic lesions were largely confined to the respiratory tract, increasing in size and number with time. Histology greatly increased the detection of the total number of lesions. The most common sites affected outside the respiratory tract were the liver and hepatic lymph nodes, but lesions were less common in peripheral lymph nodes than is observed in the natural disease. Intra-pulmonary lesions were centred on blood vessels and their associated lymphatics. Peripheral blood lymphocyte blastogenic responses to M. bovis antigens were first detected at 3 weeks after inoculation, which was 1 week after lymphocyte infiltrations were detected in the lungs, but 1 week before the majority of infections became generalised.

Conclusions. Differences in the nature of pulmonary lesions and the distribution of lesions were observed between experimentally induced and the natural disease. Rapid haematogenous and lymphatic spread occurs early in the experimentally induced disease.     

Experimental infection of brushtail possums (Trichosurus vulpecula) with Mycobacterium bovis by conjunctival instillation

In New Zealand, the brushtail possum (Trichosurus vulpecula) is the major wildlife reservoir of Mycobacterium bovis. Procedures for experimentally infecting possums are required to study the pathogenesis of the disease and to challenge possums in vaccine efficacy studies. Conjunctival instillation of a suspension of M. bovis was effective in producing bovine tuberculosis in captive possums. The experimental disease progressed slowly with the development of palpable lesions in superficial lymph node lesions, both characteristics of the disease in wild, naturally infected possums. At necropsy there was widespread distribution of macroscopic and microscopic lesions. The proportion of possums that became diseased, the rate of development and severity of lesions, the severity of clinical signs, all increased when the dose of M. bovis was increased. Of the three doses used, the medium dose (1000-2000 colony forming units) produced the disease with the most desired characteristics. As a procedure for exposing possums to infection with M. bovis the conjunctival route has advantages in that it is simple and safe to perform, and possums need only to be sedated for infection.     

Naturally occurring tuberculosis caused by Mycobacterium bovis in brushtail possums (Trichosurus vulpecula): II. Pathology

The gross and microscopic lesions due to Mycobacterium bovis infection are described in 73 brushtail possums (Trichosurus vulpeculu) from population studies and from 11 terminally ill possums. Subcutaneous lesions were suppurative in nature, often discharging through sinuses to the exterior. Histologically, the smallest lesions comprised focal aggregations of macrophages with angulated cytoplasmic boundaries occasionally containing acid-fast organisms. Larger lesions were pyogranulomatous, with extensive necrosis, caseation and large numbers of intra- and extra-cellular acid-fast organisms. Few multinucleate giant cells were seen and fibroplasia was rare. Mineralisation was recorded in tuberculous lymph nodes from only two possums. Histological evidence of haematogenous and lymphatic spread was seen in some cases.     

Ranging behaviour and duration of survival of wild brushtail possums (Trichosurus vulpecula) infected with Mycobacterium bovis

AIM: To quantify the duration of survival of possums (Trichosurus vulpecula) infected with Mycobacterium bovis, and identify aspects of their behaviour which may influence the likelihood of disease transmission to domestic stock or wildlife. METHODS: Capture and den locations of 14 naturally infected tuberculous possums, eight possums experimentally infected with M. bovis and eight non-infected possums were recorded between May 1998 and February 2000 at a study site near Castlepoint on the Wairarapa coast of the North Island in New Zealand. Denning behaviour was observed weekly using radiotelemetry, and possums were captured, examined and released bi-monthly. Data were used to estimate survival period; create denning, activity, and total ranges; and to identify extended forays by possums as individuals and groups. RESULTS: Seventeen tuberculous possum carcasses were recovered, of which 14 (82%) were close to or within their activity range. Denning ranges were known for 10/17 possums that died. Four tuberculous possums were found dead within their denning range. Three possums made extended forays in the 3 weeks before death. Twelve possums were found dead in dense scrub, three in long grass in open woodland and two on pasture. Mean duration of survival of naturally infected possums following detection of clinical signs was 3.4 months (95% CI=2.1-5.4) and the instantaneous mortality rate was 0.293 per month (95% CI=0.184-0.470). Signs of disease were obvious for about 3 weeks prior to death. Tuberculous possums were commonly trapped on only part of the area where the total non-infected population was trapped. CONCLUSION: Most tuberculous possums died within their activity range and in scrub, representing a risk of transmission of M. bovis to wildlife and livestock that forage in scrub. Smaller proportions dying on pasture represent a less frequent, but highly visible risk. Tuberculous possums were clustered on the study site, and localised possum control operations would be more effective if focussed on such areas.     

Longevity of Mycobacterium bovis in brushtail possum (Trichosurus vulpecula) carcasses,and contact rates between possums and carcasses

Abstract

AIM: To determine, for a variety of environmental conditions, how long Mycobacterium bovis might remain viable inside the carcass of a brushtail possum (Trichosurus vulpecula) that died of bovine tuberculosis (Tb), and to measure the rate of contact between free-ranging possums and possum carcasses.

METHODS: Lesions of M. bovis were simulated by inoculating excised spleens weighing 0.5–1 g with 0.2 mL liquid culture containing approximately 5 x 10⁷ cfu M. bovis/mL. Simulated lesions were inserted into possum carcasses (n=48) at the peripheral lymph nodes. Carcasses were placed in the field at two sites (a tussock grassland and a podocarp-broadleaved forest site) and in two seasons (summer and winter) for up to 62 days. Survival rates of M. bovis were estimated by sampling the simulated lesions over time, and culturing the recovered lesion to determine if any viable M. bovis bacteria were present.

The time taken for a free-ranging possum to first encounter a dead possum in its home range was estimated by live-trapping possums and fitting them with proximity loggers (n=13). A ‘contact’ was recorded if these possums came within 40–50 cm of proximity loggers fitted to possum carcasses.

RESULTS: There were strong seasonal and site effects in the survival rate of M. bovis in possum carcasses. In the grassland habitat, no viable bacilli were cultured from any carcass after 3 days in summer, whereas in winter all samples were culture-positive for the first 20 days, and some were still positive after 27 days. The survival rates for forest habitat were intermediate between the results for grassland, and there were no culture-positive carcasses after 9 days in summer or 27 days in winter.

In summer, infected carcasses (n=6) were first encountered by possums a mean 1.9 (range 0.4–6.7) days after placement.

CONCLUSIONS: Possum carcasses were contacted by free-ranging possums within the period that viable M. bovis were shown to survive in a carcass. The risk of such infection is likely to be most significant in winter or in areas with microhabitats where the survival of M. bovis is high. However, the generally low survival rate of M. bovis in possum carcasses and the low frequency of possum-to-carcass contacts indicate this route of transmission alone could not maintain Tb in a possum population.     

Poisoning with 3-nitropropionic acid in possums (Trichosurus vulpecula)

AIMS: To evaluate the toxicity, animal behavioural effects and animal welfare implications of 3-nitropropionic acid administration in possums. METHODS: The behavioural effects following 3-nitropropionic acid administration were recorded in 26 possums. RESULTS: The oral LD50 was between 110 and 170 mg/kg. Time to death averaged 9.5+/-1.9 h (mean+/-s.e.m.). Adverse signs from an animal welfare perspective were retching and restless behaviour that occurred in episodes during a period that averaged 1 h 51 min. Retching occurred in possums that were injected intraperitoneally or dosed orally with the 3-nitropropionic acid, suggesting that this effect was not necessarily initiated by gastric irritation. CONCLUSION: The potency of 3-nitropropionic acid as a toxin was low compared to other toxins that are used in possums, but it is relatively quick acting. It may cause some discomfort (retching and restlessness) prior to death.     

Effects of experimental infection with Leptospira interrogans serovar balcanica on the health of brushtail possums (Trichosurus vulpecula)

Data on changes in the condition and feeding behaviour of captive brushtail possums (Trichosurus vulpecula) following an experimental infection with Leptospira interrogans serovar balcanica are presented. The daily food intake of nine experimentally infected possums was recorded for 47 days before and 24 days after balcanica inoculation (0.5 ml intraperitoneally containing about 10(8) organisms). Body weight was recorded seven times between 42 days before and 96 days after inoculation. The mean daily food intake of infected possums decreased significantly throughout the 24-day recording period after infection with balcanica. The mean body weight of infected possums had decreased significantly by day 26 after inoculation but had fully recovered by day 96 after inoculation. Uninfected and control possums showed no significant changes in mean daily food intake or mean body weight over the experimental period. These data suggest that the health of possums is temporarily affected by infection with balcanica, but that overt disease caused by balcanica is unlikely. These findings support previous research suggesting that balcanica has only subclinical effects on possums.