A review of trends in the distribution of vector-borne diseases: is international trade contributing to their spread?

It is difficult to determine the part that international trade has played in the expansion of vector-borne diseases, because of the multitude of factors that affect the transformation of habitats and the interfaces between vectors and hosts. The introduction of pathogens through trade in live animals or products of animal origin, as well as the arrival of arthropod vectors, is probably quite frequent but the establishment of an efficient transmission system that develops into a disease outbreak remains the exception. In this paper, based on well-documented examples, the authors review the ecological and epidemiological characteristics of vector-borne diseases that may have been affected in their spread and change of distribution by international trade. In addition, they provide a detailed analysis of the risks associated with specific trade routes and recent expansions of vector populations. Finally, the authors highlight the importance, as well as the challenges, of preventive surveillance and regulation. The need for improved monitoring of vector populations and a readiness to face unpredictable epidemiological events are also emphasised, since this will require rapid reaction, not least in the regulatory context.

Impact of emergency oral rabies vaccination of foxes in northeastern Italy, 28 December 2009-20 January 2010: preliminary evaluation.

Fox rabies re-emerged in northeastern Italy in 2008, in an area bordering Slovenia. In 2009, the infection spread westward to Veneto region and in 2010 to the provinces of Trento and Bolzano. Aerial emergency oral fox vaccination was implemented in the winter 2009-10. Since this vaccination was performed at altitudes below the freezing level, a statistical analysis was conducted to evaluate its impact. Of the foxes sampled following the vaccination campaign, 77% showed a rabies antibody titre of >or=0.5 IU/ml.

Indirect estimation of porcine parvovirus maternal immunity decay in free-living wild boar (Sus scrofa) piglets by capture-recapture data.

Linear mixed regression and logspline density estimation were performed to estimate the survival curve and half life of passively acquired antibodies against porcine parvovirus (PPV) in 44 wild boar piglets captured in the Northern Apennines, Italy. One piglet had no detectable maternal antibodies at 2.5 months post partum and no antibodies were detected in any of the remaining piglets by 4 months of age. Fitted survival curves indicated that maternal antibodies were undetectable from 2.5 to 6 months of age, with a median value at 3 months and a low probability of persistent maternal antibodies after 4 months of age. The estimated half life was 23 days (95% confidence interval 22-26 days). The results agree with previous data for decay of maternally acquired antibodies against PPV in the domestic pig and indicate the value of capture-recapture analysis for the estimation of infection parameters in free-living animals.

A method to identify the areas at risk for the introduction of avian influenza virus into poultry flocks through direct contact with wild ducks.

Wild dabbling ducks are the main reservoir for avian influenza (AI) viruses and pose an ongoing threat to commercial poultry flocks. Combining the (i) size of that population, (ii) their flight distances and (iii) their AI prevalence, the density of AI-infected dabbling ducks (DID) was calculated as a risk factor for the introduction of AI viruses into poultry holdings of Emilia-Romagna region, Northern Italy. Data on 747 poultry holdings and on 39 AI primary outbreaks notified in Emilia-Romagna between 2000 and 2017 were used to validate that risk factor. A multivariable Bayesian logistic regression was performed to assess whether DID could be associated with the occurrence of AI primary outbreaks. DID value, being an outdoor flock, hobby poultry trading, species reared, length of cycle and flock size were used as explanatory variables. Being an outdoor poultry flock was significantly associated with a higher risk of AI outbreak occurrence. The probability of DID to be a risk factor for AI virus introduction was estimated to be 90%. A DID cut-off of 0.23 was identified to define high-risk areas for AI virus introduction. Using this value, the high-risk area covers 43% of the region. Seventy-four per cent of the primary AI outbreaks have occurred in that area, containing 39% of the regional poultry holdings. Poultry holdings located in areas with a high DID value should be included in a risk-based surveillance programme aimed at AI early detection.

A simulation model for low-pathogenicity avian influenza viruses in dabbling ducks in Europe.

Anseriformes are the reservoir of low-pathogenicity avian influenza viruses (LPAIV). Studies have shown a high LPAIV prevalence associated with low antibody detection in a wild duck population in northern European countries, whereas in winter areas (Mediterranean basin), low viral detection and high seroprevalence were observed. In order to gain insight into the role played by both population recruitment and migration on AIV persistence, an epidemiological model was developed. A susceptible, infectious and removed (immune or dead)-individuals model coupling population and infection dynamics was developed to simulate LPAIV circulation in dabbling ducks throughout the entire year. The transmission coefficient (beta) was calculated using the original dataset of published works, whereas dabbling duck demographic parameters were obtained from the literature. The estimated host density threshold for virus persistence is 380 susceptible individuals per day whereas the critical community size needed for maintaining the virus throughout the winter has been estimated to be about 1200 individuals. The model showed peaks of viral prevalence after nesting and during the moult period because of population recruitment and high host density, respectively. During the winter and spring periods, the viruses reach the minimal endemic level and local extinction is highly probable because of stochastic phenomena, respectively 80% and 90% of probabilities. The most sensitive parameters of the model are the recruitment rate of young susceptible animals and the duration of virus shedding.

Models of parasite biocoenosis dynamic: host density and gastrointestinal parasites in alpine chamois.

Host density is an important and widely accepted factor influencing microparasites epidemiology. In theory, host density would influence also macroparasite dynamic, although it would be achieved indirectly due to the presence of free-living infective stages of parasites. On this basis, it is expected that macroparasite abundance and prevalence would increase as host density increases, due to the higher probability for a new host to acquire infections from the environment. Nevertheless, some surveys indicate a negative relationship between host density and gastrointestinal helminth abundance in alpine chamois. On the basis of data collected from three different chamois populations, the Authors discuss the possibility that ecological factors different from host density should influence parasite biocoenosis dynamic, leading to the pattern observed in natural chamois-parasite systems.

Influenza surveillance in birds in Italian wetlands (1992-1998): is there a host restricted circulation of influenza viruses in sympatric ducks and coots?

We report the results of a 6-year serological and virological monitoring performed in ducks and coots in Italy, in order to assess the degree of influenza A virus circulation in these birds during wintering. A total of 1039 sera collected from 1992 to 1998 was screened by a double antibody sandwich blocking ELISA (NP-ELISA): seroprevalence of antibodies to influenza A viruses was significantly higher in ducks compared to coots (52.2% vs. 7.1%, respectively). The hemagglutination-inhibition (HI) assay, performed on NP-ELISA positive sera, showed that 16.9% of these duck sera and 33.3% of these coot sera had antibodies to at least one influenza virus HA subtype: ducks showed HI antibodies against most of the HA subtypes, except for the H3, H4, H7, and H12; coots were seropositive to the H3 and H10 subtypes, only. From 1993 to 1998, 22 virus strains were obtained from 802 cloacal swabs, with an overall virus isolation frequency of 2.7%. Viruses belonging to the H1N1 subtype were by far the most commonly circulating strains (18/22) and were isolated mainly from ducks (17/18). The remaining viruses were representative of the H10N8, H5N2 and H3N8 subtypes. Our data indicate some differences between influenza A virus circulation in sympatric ducks and coots and a significant antigenic diversity between some reference strains and viruses recently isolated in Italy.

Circulation of influenza viruses in wild waterfowl wintering in Italy during the 1993-99 period: evidence of virus shedding and seroconversion in wild ducks.

The mechanisms of perpetuation of influenza A viruses in aquatic birds, their main reservoir in nature, have not yet been completely clarified. One hypothesis is that they continue to circulate in waterfowl throughout the year, even though virus isolations during the winter months are rare. We analyzed influenza virus circulation in wild ducks in Italy during six winter seasons (1993-99), using virus isolations and serological analyses. It was apparent that influenza A viruses were constantly circulating in wild birds during all the seasons considered. Moreover, seroconversion rates (obtained from ducks recaptured during the same season) suggest a frequency of influenza infections higher than expected on the basis of the virus isolation rates.

Control of infectious diseases of wildlife in Europe.

During the last 30 years, new epidemiological patterns have emerged as free-ranging wildlife have become progressively more involved in the epidemiology of both common and emerging infectious diseases of humans and domestic animals. This has been seen in rabies, bovine tuberculosis and more recently in wild-boar classical swine fever. Emerging diseases are of interest to veterinarians as well as public health officials but attempts to control these diseases have not always been successful as in wildlife populations control of either host or pathogen can present particular problems. Lessons should be learnt from previous experiences to help in the management of new emerging diseases in the future.

Classical swine fever (hog cholera) in wild boar in Europe.

Classical swine fever (CSF) is of increasing concern in Europe where wild boar appear to play an important epidemiological role. In most parts of the continent, demographic trends are on the increase, due to improvement in game management. As a result of higher densities, populations become more susceptible to various infectious diseases, among which CSF is cause for particular concern. Wild boar do not appear to be a classic reservoir in most cases, but nevertheless may perpetuate foci of infection over the long term, constituting a real threat for the pig farming industry. Since the infection does not appear to spread easily in natural populations of free-ranging wild boars, control of the disease may be feasible. However, most of the appropriate measures, such as banning hunting, are not considered acceptable. Consequently, the expertise of wildlife disease specialists is required to help solve the problem when it occurs.

[Parasites present in foxes (Vulpes vulpes) of the province of Forli]. / Parassiti presenti in volpi (Vulpes vulpes) della provincia di Forli.

In the period March 1983 - March 1984 a parasitological survey was carried out on 103 foxes killed in the Forli province (Italy). The parasites identified were: Toxocara canis (45.6%); Uncinaria stenocephala (14.6%); Mesocestoides lineatus (9.7%); Dipylidium caninum (2.9%); Taenia crassiceps (2.9%); Trichuris vulpis (2.9%). Out of all the cestodes found in 7 animals the authors identified only genus Taenia since their preservation conditions were not optimal. Other 13 subjects contained many cestodes similar to T. hydatigena, but considerably shorter in the mean length (20 cm vs 200). In a fecal sample the authors found a species of coccidium whose features do not correspond to any of those described in foxes, therefore it was called Eimeria sp. Finally, the autopsies' results were compared with coprological ones in order to asses their reliability.

Intestinal helminth parasite community in wolves (Canis lupus) in Italy.

From 1987 to 1993, 89 wolves (Canis lupus) collected throughout the whole Italian range were examined for intestinal helminth parasites. Twelve species were found, including 5 nematodes (Uncinaria stenocephala, Toxocara canis, Ancylostoma caninum, Trichuris vulpis and Toxascaris leonina) and 7 cestodes (Echinococcus granulosus, Taenia hydatigena, T. multiceps, T. pisiformis, T. ovis, Mesocestoides lineatus and Dipylidium caninum). No significant differences were detected between sexes. T. canis showed higher prevalence and numbers in youngs, while E. granulosus and T. vulpis in adults. Interference between U. stenocephala and A. caninum was detected. Parasite biocenosis was stable in respect to geographical and ecological variables.

Echinococcus granulosus in the wolf in Italy.

During the period 1987-1999, 119 wolf cadavers were examined and checked for the presence of Echinococcus granulosus. All the animals were retrieved along the whole Apennines range of distribution of the species in Italy and most of them were illegally killed. Eighteen wolves resulted positive (15%). The mean intensity was 697.5. The force of infection for prevalence was 8.2 year(-1). The prevalence of the parasite was significantly and positively influenced by the local prevalence of cystic echinococcosis (CE) in sheep. Mean intensity was significantly and positively influenced by both the age of the wolf and the prevalence of CE in sheep. A deterministic model was used in order to simulate a purely theoretical sylvatic cycle of the parasites having the wolf as the only definitive host with 15% of prevalence. The expected prevalence of CE in wild intermediate species ranges between 10% and 25%. This prevalence overlaps the one observed in sheep. Even if both the wolf and the wild ungulate populations are increasing, the wolf still acts as a part of the main dog-sheep cycle of the parasite.

The parasites of the badger (Meles meles) in the north of Mugello (Florence, Italy).

During the period January 1993-June 1994, a parasitological survey was carried out on 19 badgers (Meles meles) road killed in Northern Mugello (Florence). The following helminths (together with their prevalence) were isolated and classified: Uncinaria criniformis (84.2%); Capillaria sp. (31.6%); Molineus patens (21.1%); Mesocestoides melesi (21.1%); Aelurostrongylus falciformis (52.6%); Crenosoma melesi (21.1%). According to results, only sex related differences in prevalence were studied. The parasite biocenosis is composed exclusively by dominant and codominant species. Mesocestoides melesi represents the first record for Italy. All the species found fitted a negative binomial distribution.

Detection of canine parvovirus in wolves from Italy.

One hundred fifteen samples of wolf (Canis lupus) feces were collected during 1994 to 1995 from four free-living populations of the north central Apennines Mountains, Italy. The samples were tested for canine parvovirus by antigen-capture enzyme-linked immunosorbent assay (ELISA), hemagglutination, and virus isolation. Four of these samples were positive by virus isolation as confirmed by electron microscopy. All positive samples were from Casentino Park in Tuscany. This is the first definitive observation of canine parvovirus in wolves from Europe.

Animals as hosts of zoonoses.

The different aspects of the host/parasite relationships are taken into consideration along with the factors that can affect their behavioural patterns. Special attention has been given to the conditions which are involved in the development and establishment of the host/parasite association with an account of the various forms of this coexistence, such as proper parasitism, mutualism, commensalism and symbiosis. The rules which must be complied with to secure the survival of parasites and the perpetuation and completion of the parasitic life cycles are described. The special role of man as a host of zoonotic agents and the main approaches to zoonoses control are considered.

Wildlife veterinarian, conservation and public health.

In recent years wildlife diseases (infectious and non-infectious) have played a relevant role in both wildlife conservation and public health. Global environmental changes have determined a bimodal evolution of wildlife. On one side a huge loss of biodiversity has been observed leading to the increasing of threatened or endangered species. In contrast few opportunistic taxa increased their aboundances and ranges. The above scenarios claim the intervention of wildlife veterinarians. In conservation the understanding of the ecological role of the host parasite relationship and the perturbations on the host population dynamics have to be assessed and eventually modified. In public health the increased overlapping among wildlife, livestock, pets and human beings represents a risk for diseases spread (no matter in which directions). Serious limits are, still now, observed in the acceptance of this 'new world' by veterinary academics. As a consequence curricula often fail in providing adequate skill at both undergraduate and graduate levels. An addressed approach towards wildlife diseases should be promoted as an essential component of environmental management.