Does interspecific competition have a moderating effect on Taenia solium transmission dynamics in Southeast Asia?

Zoonotic helminths - why the challenge remains

Helminth zoonoses remain a global problem to public health and the economy of many countries. Polymerase chain reaction-based techniques and sequencing have resolved many taxonomic issues and are now essential to understanding the epidemiology of helminth zoonotic infections and the ecology of the causative agents. This is clearly demonstrated from research on Echinococcus (echinococcosis) and Trichinella (trichinosis). Unfortunately, a variety of anthropogenic factors are worsening the problems caused by helminth zoonoses. These include cultural factors, urbanization and climate change. Wildlife plays an increasingly important role in the maintenance of many helminth zoonoses making surveillance and control increasingly difficult. The emergence or re-emergence of helminth zoonoses such as Ancylostoma ceylanicum, Toxocara, Dracunculus and Thelazia exacerbate an already discouraging scenario compounding the control of a group of long neglected diseases.

Co-infection of pigs with Taenia solium cysticercosis and gastrointestinal parasites in Eastern and Western Uganda

A study was carried out in Kamuli and Hoima districts in Eastern and Western regions of Uganda to determine the Taenia solium porcine cysticercosis (PCC) and gastrointestinal (GI) parasites co-infection status in pigs. One hundred sixty-one households were selected randomly and visited between November and December 2019. A household questionnaire was administered, and faecal and blood samples were collected from at least one pig older than 3 months per household. A blood sample was obtained from a jugular venipuncture, and a rectal faecal sample was obtained. Taenia spp. circulating antigen levels in the sample sera were tested using a commercial enzyme-linked immunosorbent assay kit, apDia™ cysticercosis Ag ELISA. The modified McMaster technique was used to identify and quantify the GI parasites. The apparent animal-level seroprevalence for PCC was 4.8% (95% CI 2.7–7.1) and differed across the two districts (p = 0.018). At the pig herd level, the prevalence was 9.7% (95% CI 5.5–14.4). The prevalence of the different nematode eggs and coccidian oocysts in the two districts was as follows: strongyles 79.0% (95% CI 74.3–83.6), coccidia 73.3% (95% CI 68.3–78.6), Trichuris spp. 7.4% (95% CI 4.9–10.6), Strongyloides ransomi 2.1 (95% CI 0.7–3.5) and Ascaris spp. 4.9 (95% CI 2.8–7.4). Overall, across the two districts, the arithmetic mean for the oocysts per gram (OPG) for coccidia was 2042.2 ± 5776.1, and eggs per gram (EPG) were the highest in strongyles 616.1 ± 991. Overall, 57.4% of the porcine cysticercosis seropositive pigs were also positive for at least one of the gastrointestinal helminths which included strongyles, Strongyloides ransomi, Trichuris spp. and Ascaris spp. The co-infection status of pigs with both PCC and GI parasites demonstrated by this study can provide an incentive for integrating the control and management of both parasites with oxfendazole. Further studies are required to understand the feasibility of using oxfendazole including cost–benefit analysis and the acceptability by local stakeholders for the control of T. solium cysticercosis and gastrointestinal parasites in pigs.

The genome of the thin-necked bladder worm Taenia hydatigena reveals evolutionary strategies for helminth survival

Taenia hydatigena is a widespread gastrointestinal helminth that causes significant health problems in livestock industry. This parasite can survive in a remarkably wide range of intermediate hosts and affects the transmission dynamics of zoonotic parasites. T. hydatigena is therefore of particular interest to researchers interested in studying zoonotic diseases and the evolutionary strategies of parasites. Herein we report a high-quality draft genome for this tapeworm, characterized by some hallmarks (e.g., expanded genome size, wide integrations of viral-like sequences and extensive alternative splicing during development), and specialized adaptations related to its parasitic fitness (e.g., adaptive evolutions for teguments and lipid metabolism). Importantly, in contrast with the evolutionarily close trematodes, which achieve gene diversification associated with immunosuppression by gene family expansions, in T. hydatigena and other cestodes, this is accomplished by alternative splicing and gene loss. This indicates that these two classes have evolved different mechanisms for survival. In addition, molecular targets for diagnosis and intervention were identified to facilitate the development of control interventions. Overall, this work uncovers new strategies by which helminths evolved to interact with their hosts.

Taenia solium taeniasis/cysticercosis: From parasite biology and immunology to diagnosis and control

Infection with the pork tapeworm (Taenia solium) is responsible for a substantial global burden of disease, not only restricted to its impact on human health, but also resulting in a considerable economic burden to smallholder pig farmers due to pig cysticercosis infection. The life-cycle, parasitology and immunology of T. solium are complex, involving pigs (the intermediate host, harbouring the larval metacestode stage), humans (the definitive host, harbouring the adult tapeworm, in addition to acting as accidental intermediate hosts) and the environment (the source of infection with eggs/proglottids). We review the parasitology, immunology, and epidemiology of the infection associated with each of the T. solium life-cycle stages, including the pre-adult/adult tapeworm responsible for human taeniasis; post-oncosphere and cysticercus associated with porcine and human cysticercosis, and the biological characteristics of eggs in the environment. We discuss the burden associated, in endemic settings, with neurocysticercosis (NCC) in humans, and the broader cross-sectoral economic impact associated both with NCC and porcine cysticercosis, the latter impacting food-value chains. Existing tools for diagnostics and control interventions that target different stages of the T. solium transmission cycle are reviewed and their limitations discussed. Currently, no national T. solium control programmes have been established in endemic areas, with further work required to identify optimal strategies according to epidemiological setting. There is increasing evidence suggesting that cross-sectoral interventions which target the parasite in both the human and pig host provide the most effective approaches for achieving control and ultimately elimination. We discuss future avenues for research on T. solium to support the attainment of the goals proposed in the revised World Health Organisation neglected tropical diseases roadmap for 2021-2030 adopted at the 73rd World Health Assembly in November 2020.

Performance of Ag-ELISA in the diagnosis of Taenia solium cysticercosis in naturally infected pigs in Tanzania

Background

Taenia solium is a zoonotic parasite responsible for neurocysticercosis—a major cause of late-onset acquired epilepsy in humans. Lack of affordable, specific and sensitive diagnostic tools hampers control of the parasite. This study assessed the performance of an antigen detection enzyme-linked immunosorbent assay (Ag-ELISA) in the diagnosis of viable T. solium cysticercosis in naturally infected slaughter-age pigs in an endemic area in Tanzania.

Methods

A total of 350 pigs were bled before they were slaughtered and their carcases examined. Serum was analyzed for circulating antigens by using a monoclonal antibody-based B158/B60 Ag-ELISA. Each carcase was examined for the presence of Taenia hydatigena cysticerci and half carcase musculature together with the whole brain, head muscles, tongue, heart and diaphragm were sliced with fine cuts (< 0.5 cm) to reveal and enumerate T. solium cysticerci. Half carcase dissection can detect at least 84% of infected pigs. Prevalence and their 95% confidence intervals (CI) were calculated in Stata 12. Sensitivity, specificity, predictive values and likelihood ratios were determined.

Results

Twenty–nine pigs (8.3%, 95% CI: 5.6–11.7%) had viable T. solium cysticerci while 11 pigs had T. hydatigena cysticerci (3.1%, 95% CI: 1.6–5.5%). No co-infection was observed. Sixty-eight pigs (19.4%, 95% CI: 15.4–20%) tested positive on Ag-ELISA; of these, 24 had T. solium cysticerci and 7 had T. hydatigena cysticerci. Sensitivity and specificity were determined to be 82.7% and 86.3%, respectively. Positive and negative predictive values were 35.2% and 98.2%, respectively. Likelihood ratios for positive and negative Ag-ELISA test results were 6.0 and 0.2, respectively. There was a significant positive correlation between the titre of circulating antigens and intensity of T. solium cysticerci (r₍₃₄₈₎ = 0.63, P < 0.001).

Conclusions

The Ag-ELISA test characteristics reported in this study indicate that the test is more reliable in ruling out T. solium cysticercosis in pigs, than in confirming it. Hence, a negative result will almost certainly indicate that a pig has no infection, but a positive result should always be interpreted with caution. Estimates of T. solium prevalence based on Ag-ELISA results should, therefore, be adjusted for test performance characteristics and occurrence of T. hydatigena.

A comparison of Taenia solium and Taenia hydatigena infection in pigs using serological diagnosis and post-mortem inspection methods in Benoué division, North Cameroon

The metacestodes of Taenia solium and Taenia hydatigena are the cause of cysticercosis in pigs. T. solium is also responsible of the taeniosis/neurocysticercosis complex in humans, constituting a main cause of epilepsy cases across endemic countries. T. hydatigena is non-zoonotic, but its occurrence in pigs contributes significantly to false positive reactions should genus-species serological methods be used for diagnosis of T. solium porcine cysticercosis. T. hydatigena is often considered not common in pigs in Africa compared to T. solium. On the basis of the evidence that these two cestodes coexist in Cameroon, we examined the viscera of 305 pigs for the identification of the metacestodes of T. hydatigena in Bénoué division, North Region of Cameroon. Tongue, masticatory muscles and heart were sliced for the identification of T. solium cysticerci (TMH dissection test). Twenty seven (8.85%) and 16 (5.24%) pigs were found infected with the metacestodes of T. solium and T. hydatigena, respectively. The difference between the two rates of infection was not statistically significant (P > 0.05). Serum samples were also collected for the evaluation of an inhibition ELISA (i-ELISA) specific to antibodies anti- T. solium or anti-T. hydatigena cysticerci. After incubation of these sera with cyst fluid of T. solium, T. hydatigena, T. multiceps multiceps, T. multiceps gaigeri and T. saginata to eliminate cross-reactions among cestodes parasites, the i-ELISA indicated that 26.56% and 28.52% slaughtered pigs had predominant specific antibodies to cyst fluid of T. solium and T. hydatigena, respectively. Combination of TMH dissection test, i-ELISA and a standard indirect ELISA in a Bayesian simulation approach revealed a true prevalence of 19.27% (0.7-49.27, CI 95%) and 24.85% (5.17-48.34, CI 95%) of porcine cysticercosis due to T. solium and T. hydatigena, respectively. These results indicated that T. hydatigena is as prevalent as T. solium in pigs in the North of Cameroon.

Prevalence of porcine Taenia solium and Taenia hydatigena cysticercosis in Cameroon

Taenia solium, a zoonotic tapeworm species of human and pigs, has been targeted by the World Health Organisation (WHO) for elimination in endemic areas of Africa, Latin America and some parts of Asia. Unfortunately, the assessment of control measures against T. solium is complicated by the lack of specificity of current immunodiagnostic techniques for diagnosis of porcine cysticercosis. Many authors have concluded that the prevalence of T. hydatigena in pigs in Africa is low and extensive epidemiological studies on T. solium cysticercosis in pigs have been carried out using serological tests that cannot differentiate the taeniid species. To estimate and compare the prevalence of T. solium and T. hydatigena in pigs in Cameroon, we examined 416 slaughtered pigs at a pig abattoir in Yaoundé city with the animals originating from several parts of the country. At post-mortem inspection, 35 pigs (8.4%; 95% Confidence Interval (CI), 5.9-11.5 %) were found infected exclusively with T. solium and 27 (6.5%; 95% CI, 4.3-9.3 %) infected exclusively with T. hydatigena metacestodes. One animal was infected with T. solium and T. hydatigena. A stochastic simulation model which took into account the sensitivity of dissection of the tongue, external masseters and heart for diagnosis of T. solium porcine cysticercosis (TMH dissection test) and examination of mesentery, surfaces of the intestines and liver to identify T. hydatigena cysticerci in slaughtered pigs was developed to estimate the prevalence of these taeniid species. The results revealed that the actual prevalence of T. solium and T. hydatigena in Cameroon were 24.8% (95% CI, 20.1-30.5%) and 19.2% (95% CI, 15.1-24.1%), respectively. This study reports the highest porcine T. hydatigena prevalence ever in Africa and adjusted the prevalence of porcine T. solium infection obtained with genus-specific Ag-ELISA (Dorny et al., 2000) in Cameroon due to the presence of T. hydatigena.

Molecular analyses reveal two geographic and genetic lineages for tapeworms, Taenia solium and Taenia saginata, from Ecuador using mitochondrial DNA

Tapeworms Taenia solium and Taenia saginata are the causative agents of taeniasis/cysticercosis. These are diseases with high medical and veterinary importance due to their impact on public health and rural economy in tropical countries. The re-emergence of T. solium as a result of human migration, the economic burden affecting livestock industry, and the large variability of symptoms in several human cysticercosis, encourage studies on genetic diversity, and the identification of these parasites with molecular phylogenetic tools. Samples collected from the Ecuadorian provinces: Loja, Guayas, Manabí, Tungurahua (South), and Imbabura, Pichincha (North) from 2000 to 2012 were performed under Maximum Parsimony analyses and haplotype networks using partial sequences of mitochondrial DNA, cytochrome oxidase subunit I (COI) and NADH subunit I (NDI), from Genbank and own sequences of Taenia solium and Taenia saginata from Ecuador. Both species have shown reciprocal monophyly, which confirms its molecular taxonomic identity. The COI and NDI genes results suggest phylogenetic structure for both parasite species from south and north of Ecuador. In T. solium, both genes gene revealed greater geographic structure, whereas in T. saginata, the variability for both genes was low. In conclusion, COI haplotype networks of T. solium suggest two geographical events in the introduction of this species in Ecuador (African and Asian lineages) and occurring sympatric, probably through the most common routes of maritime trade between the XV-XIX centuries. Moreover, the evidence of two NDI geographical lineages in T. solium from the north (province of Imbabura) and the south (province of Loja) of Ecuador derivate from a common Indian ancestor open new approaches for studies on genetic populations and eco-epidemiology.

Taenia hydatigena cysticercosis in slaughtered pigs, goats, and sheep in Tanzania

Few studies have been carried out in Africa to estimate the prevalence of Taenia hydatigena. With the aim to determine the prevalence of T. hydatigena in slaughtered pigs and small ruminants (goats and sheep) in Mbeya, Tanzania, two cross-sectional surveys were carried out investigating pigs in April to May 2014 and small ruminants in September 2012. In total, 243 pigs were examined post-mortem for T. hydatigena cysts which were found in 16 (6.6 %) pigs. The majority (80 %) of cysts were found on the omentum and the rest on the liver (20 %), all on the visceral surface. Two pigs were also found infected with Taenia solium but showed no signs of other infections. A total of 392 goats and 27 sheep were examined post-mortem, and the prevalence of T. hydatigena was similar in goats and sheep with 45.7 and 51.9 %, respectively. DNA sequencing of the mitochondrial cytochrome c oxidase subunit 1 gene (cox1) from a subsample of metacestodes from goats and sheep confirmed the T. hydatigena infection. The prevalence found in small ruminants was comparable to other studies conducted in Africa, but for pigs, it is one of the highest recorded to date. The present study also confirms the occurrence of T. hydatigena and T. solium in pigs from Mbeya. Further studies are needed to determine the impact of T. hydatigena on production under sub-Saharan conditions and the financial consequences for smallholder farmers.

Taenia solium Human Cysticercosis: A Systematic Review of Sero-epidemiological Data from Endemic Zones around the World

Background

Taenia solium cysticercosis is a zoonotic neglected disease responsible for severe health disorders such as seizures and death. Understanding the epidemiology of human cysticercosis (HCC) in endemic regions will help to expose critical information about the transmission of the disease, which could be used to design efficient control programs. This review gathered serological data on apparent prevalence of T. solium circulating antigens and/or seroprevalence of T. solium antibodies, apparent prevalence of human taeniasis and risk factors for HCC from endemic communities in order to understand the differences in exposure to the parasite and active infections with T. solium metacestodes in endemic areas around the world.

Methods

Three databases were used to search sero-epidemiological data from community-based studies conducted between 1989 and 2014 in cysticercosis endemic communities worldwide. The search focused on data obtained from T. solium circulating antigen detection by monoclonal antibody-based sandwich ELISA and/or T. solium antibody seroprevalence determined by Enzyme-linked Immunoelectrotransfer Blot (EITB). A meta-analysis was performed per continent.

Principal Findings

A total of 39,271 participants from 19 countries, described in 37 articles were studied. The estimates for the prevalence of circulating T. solium antigens for Africa, Latin America and Asia were: 7.30% (95% CI [4.23–12.31]), 4.08% (95% CI [2.77–5.95]) and 3.98% (95% CI [2.81–5.61]), respectively. Seroprevalence estimates of T. solium antibodies were 17.37% (95% CI [3.33–56.20]), 13.03% (95% CI [9.95–16.88]) and 15.68% (95% CI [10.25–23.24]) respectively. Taeniasis reported prevalences ranged from 0 (95% CI [0.00–1.62]) to 17.25% (95% CI [14.55–20.23]).

Significance

A significant variation in the sero-epidemiological data was observed within each continent, with African countries reporting the highest apparent prevalences of active infections. Intrinsic factors in the human host such as age and immunity were main determinants for the occurrence of infections, while exposure was mostly related to environmental factors which varied from community to community.

Human cysticercosis is a neglected zoonotic disease caused by the larval stage of the parasite Taenia solium. This disease is responsible for severe health disorders such as seizures, and in some cases even death. T. solium cysticercosis is endemic in countries in Africa, Latin America and Asia where conditions such as inadequate hygiene, poor sanitary conditions, open defecation, free roaming pigs and poverty permit the transmission of the disease. Diagnostic tools are capable of detecting exposure to eggs and infection levels in a population through antibody and antigen detection, respectively. This review focused on gathering epidemiological data from endemic communities in Africa, Latin America and Asia in order to understand the causes of the observed variations in exposure/infection patterns in endemic regions. Similar antibody seroprevalences were observed worldwide while infection prevalences varied significantly within each region. Intrinsic factors such as age and immunity were determining factors for the occurrence of infections, while exposure was related to environmental factors which varied from region to region. Understanding the epidemiology of cysticercosis in endemic regions will help expose information on the transmission, which could in turn be used to design appropriate control programs.

Recent advances and perspectives in molecular epidemiology of Taenia solium cysticercosis

Cysticercosis caused by accidental ingestion of eggs of Taenia solium is spreading all over the world through globalization and is one of the most neglected, neglected tropical diseases (NTDs) or neglected zoonotic diseases (NZDs). In the present study, the reason why T. solium cysticercosis has been neglected is discussed at first, and followed with an overview on the most recent advances and perspectives in molecular approaches for epidemiology of T. solium taeniasis/cysticercosis, since although taeniasis does not constitute recognized zoonoses, transmission and complete development are dependent on human definitive hosts. Main topics are discussions on (1) the two, Asian and Afro/American, genotypes of T. solium, (2) comparative analysis of mitochondrial (haploid) and nuclear (diploid) genes, and (3) the presence of hybrids of these two genotypes which indicates out-crossing of two genotypes in hermaphrodite tapeworms in Madagascar. Additional topics are on (4) the usefulness of phylogeographic analyses to discuss where the infection was acquired from, and (5) miscellaneous unsolved topics around these genetic diversity of T. solium.

Prevalence of Endemic Pig-Associated Zoonoses in Southeast Asia: A Review of Findings from the Lao People's Democratic Republic

The increasing intensification of pork production in southeast Asia necessitates an urgent requirement to better understand the dual impact of pig-associated zoonotic disease on both pig production and human health in the region. Sharing porous borders with five countries and representing many regional ethnicities and agricultural practices, the Lao People's Democratic Republic (Lao PDR) appears well placed to gauge the levels of pig-associated zoonoses circulating in the wider region. Despite this, little is known about the true impact of zoonotic pathogens such as leptospirosis, Trichinella, hepatitis E virus (HEV), Japanese encephalitis (JE), and Taenia solium on human health and livestock production in the country. A comprehensive review of the published prevalences of these five pig-associated zoonoses in Lao PDR has demonstrated that although suspicion remains high of their existence in pig reservoirs across the country, epidemiological data are scarce; only 31 epidemiological studies have been undertaken on these diseases in the past 25 years. A greater understanding of the zoonoses prevalence and subsequent risks associated with pork production in the southeast Asian region could help focus public health and food safety interventions at key points along the value chain, benefiting both livestock producers and the broader animal and human health systems in the region.

Immunology of Taenia solium taeniasis and human cysticercosis

The life cycle of Taenia solium, the pork tapeworm, is continuously closed in many rural settings in developing countries when free roaming pigs ingest human stools containing T. solium eggs and develop cysticercosis, and humans ingest pork infected with cystic larvae and develop intestinal taeniasis, or may also accidentally acquire cysticercosis by faecal-oral contamination. Cysticercosis of the human nervous system, neurocysticercosis, is a major cause of seizures and other neurological morbidity in most of the world. The dynamics of exposure, infection and disease as well as the location of parasites result in a complex interaction which involves immune evasion mechanisms and involutive or progressive disease along time. Moreover, existing data are limited by the relative lack of animal models. This manuscript revises the available information on the immunology of human taeniasis and cysticercosis.

Temporal and spatial dynamics of trypanosomes infecting the brush-tailed bettong (Bettongia penicillata): a cautionary note of disease-induced population decline

BACKGROUND

The brush-tailed bettong or woylie (Bettongia penicillata) is on the brink of extinction. Its numbers have declined by 90% since 1999, with their current distribution occupying less than 1% of their former Australian range. Woylies are known to be infected with three different trypanosomes (Trypanosoma vegrandis, Trypanosoma copemani and Trypanosoma sp. H25) and two different strains of T. copemani that vary in virulence. However, the role that these haemoparasites have played during the recent decline of their host is unclear and is part of ongoing investigation.

METHODS

Woylies were sampled from five locations in southern Western Australia, including two neighbouring indigenous populations, two enclosed (fenced) populations and a captive colony. PCR was used to individually identify the three different trypanosomes from blood and tissues of the host, and to investigate the temporal and spatial dynamics of trypanosome infections.

RESULTS

The spatial pattern of trypanosome infection varied among the five study sites, with a greater proportion of woylies from the Perup indigenous population being infected with T. copemani than from the neighbouring Kingston indigenous population. For an established infection, T. copemani detection was temporally inconsistent. The more virulent strain of T. copemani appeared to regress at a faster rate than the less virulent strain, with the infection possibly transitioning from the acute to chronic phase. Interspecific competition may also exist between T. copemani and T. vegrandis, where an existing T. vegrandis infection may moderate the sequential establishment of the more virulent T. copemani.

CONCLUSION

In this study, we provide a possible temporal connection implicating T. copemani as the disease agent linked with the recent decline of the Kingston indigenous woylie population within the Upper Warren region of Western Australia. The chronic association of trypanosomes with the internal organs of its host may be potentially pathogenic and adversely affect their long term fitness and coordination, making the woylie more susceptible to predation.

Filaria zoogeography in Africa: ecology, competitive exclusion, and public health relevance

Six species of filariae infect humans in sub-Saharan Africa. We hypothesise that these nematodes are able to polyparasitise human hosts by having successfully, through competitive exclusion, adapted to distinct niches. Despite inhabiting the same host, adult stages reside in different tissue sites. Microfilariae of some species exhibit temporal separation by reaching peak levels in the blood at specific times of day. Spatial and temporal distributions in microfilaria location are exploited by the vector feeding-behaviour whereas adult survival is enhanced by occupying exclusive 'ecological' niches of the body. We present specific examples to demonstrate this concept, which is not only important from the biological aspect but important in the context of elimination programmes.

Epidemiology and genetic diversity of Taenia asiatica: a systematic review

Taenia asiatica has made a remarkable journey through the scientific literature of the past 50 years, starting with the paradoxical observation of high prevalences of T. saginata-like tapeworms in non-beef consuming populations, to the full description of its mitochondrial genome. Experimental studies conducted in the 1980s and 1990s have made it clear that the life cycle of T. asiatica is comparable to that of T. saginata, except for pigs being the preferential intermediate host and liver the preferential location of the cysts. Whether or not T. asiatica can cause human cysticercosis, as is the case for Taenia solium, remains unclear. Given the specific conditions needed to complete its life cycle, in particular the consumption of raw or poorly cooked pig liver, the transmission of T. asiatica shows an important ethno-geographical association. So far, T. asiatica has been identified in Taiwan, South Korea, Indonesia, the Philippines, Thailand, south-central China, Vietnam, Japan and Nepal. Especially this last observation indicates that its distribution is not restricted to South-East-Asia, as was thought so far. Indeed, the molecular tools developed over the last 20 years have made it increasingly possible to differentiate T. asiatica from other taeniids. Such tools also indicated that T. asiatica is related more closely to T. saginata than to T. solium, feeding the debate on its taxonomic status as a separate species versus a subspecies of T. saginata. Furthermore, the genetic diversity within T. asiatica appears to be very minimal, indicating that this parasite may be on the verge of extinction. However, recent studies have identified potential hybrids between T. asiatica and T. saginata, reopening the debate on the genetic diversity of T. asiatica and its status as a separate species.

A review of foodborne bacterial and parasitic zoonoses in Vietnam

Vietnam has experienced unprecedented economic and social development in recent years, and the livestock sector is undergoing significant transformations. Although food animal production is still dominated by small-scale 'backyard' enterprises with mixed crop-livestock or livestock-aquatic systems, there is a trend towards more intensive and vertically integrated operations. Changes in animal production, processing and distribution networks for meat and animal products, and the shift from wet markets to supermarkets will undoubtedly impact food safety risks in Vietnam in unforeseen and complex ways. Here, we review the available published literature on bacterial and parasitic foodborne zoonoses (FBZ) in Vietnam. We report on clinical disease burden and pathogen prevalence in animal reservoirs for a number of important FBZ, and outline opportunities for future research.

Parasite co-infections show synergistic and antagonistic interactions on growth performance of East African zebu cattle under one year

The co-occurrence of different pathogen species and their simultaneous infection of hosts are common, and may affect host health outcomes. Co-infecting pathogens may interact synergistically (harming the host more) or antagonistically (harming the host less) compared with single infections. Here we have tested associations of infections and their co-infections with variation in growth rate using a subset of 455 animals of the Infectious Diseases of East Africa Livestock (IDEAL) cohort study surviving to one year. Data on live body weight, infections with helminth parasites and haemoparasites were collected every 5 weeks during the first year of life. Growth of zebu cattle during the first year of life was best described by a linear growth function. A large variation in daily weight gain with a range of 0·03-0·34 kg, and a mean of 0·135 kg (0·124, 0·146; 95% CI) was observed. After controlling for other significant covariates in mixed effects statistical models, the results revealed synergistic interactions (lower growth rates) with Theileria parva and Anaplasma marginale co-infections, and antagonistic interactions (relatively higher growth rates) with T. parva and Theileria mutans co-infections, compared with infections with T. parva only. Additionally, helminth infections can have a strong negative effect on the growth rates but this is burden-dependent, accounting for up to 30% decrease in growth rate in heavily infected animals. These findings present evidence of pathogen-pathogen interactions affecting host growth, and we discuss possible mechanisms that may explain observed directions of interactions as well as possible modifications to disease control strategies when co-infections are present.

Taenia asiatica: the most neglected human Taenia and the possibility of cysticercosis

Not only Taenia solium and Taenia saginata, but also Taenia asiatica infects humans. The last species is not included in the evaluation of the specificity of the immunodiagnostic techniques for taeniasis/cysticercosis. There is currently no specific immunodiagnostic method for T. asiatica available. Therefore, due to the fact that molecular techniques (the only tool to distinguish the 3 Taenia species) are normally not employed in routine diagnostic methods, the 2 questions concerning T. asiatica (its definite geographic distribution and its ability to cause human cysticercosis), remain open, turning T. asiatica into the most neglected agent of human taeniasis-cysticercosis.

A cross-sectional study of Taenia solium in a multiple taeniid-endemic region reveals competition may be protective

We conducted cross-sectional surveys for taeniasis and cysticercosis in humans, pigs, and dogs in four northern provinces of Laos. Human cysticercosis and taeniasis prevalence was 2.2% (95% confidence interval [CI] = 1.4-3.0%) and 8.4% (95% CI = 6.9-9.9%), respectively. Eating uncooked beef, being male, province of residence, age, and ethnicity were significant risk factors for taeniasis and only province of residence was a significant risk factor for cystiercosis. Thirty-five human tapeworms were recovered during the survey and 33 (94.3%) and 2 (5.7%) were identified as Taenia saginata and T. solium, respectively. Maximum-likelihood adjusted prevalence of T. solium and T. hydatigena in pigs was 4.2% (95% CI = 0.5-7.9%) and 55.9% (95% CI = 47.5-64.3%), respectively, and T. hydatigena taeniasis in dogs was 4.8% (95% CI = 0.0-11.3%). Taenia hydatigena and T. saginata were the most prevalent taeniids in the respective pig and human populations and together may suppress T. solium transmission.

Assessing the burden of human cysticercosis in Vietnam

OBJECTIVES

To describe the occurrence of cysticercosis in patients living in rural areas of Northern Vietnam presenting clinical signs of neurocysticercosis.

METHODS

Serological antigen detection, reflecting current infection with viable larval stages of Taenia solium, was used to estimate the prevalence of active cysticercosis in this patient population.

RESULTS

The seroprevalence in epileptic patient population was <10%. However, antigen detection cannot detect dead cysticerci, which may also cause clinical signs. Therefore, the seroprevalence figures shown here may underestimate the role of neurocysticercosis as a causal agent of epilepsy and headaches in this population.

CONCLUSIONS

Human and porcine cysticercosis remain public and veterinary public health problems in Northern Vietnam and probably in other parts of the country.

Epidemiology of Taenia solium in Nepal: is it influenced by the social characteristics of the population and the presence of Taenia asiatica?

The transmission of the zoonotic pork tapeworms Taenia solium and T. asiatica depends on a combination of specific risk factors, such as open defecation, backyard pig raising and the consumption of raw or undercooked pork and viscera. A community-based survey was conducted among 289 households in south-eastern Nepal to study the heterogeneity of these risk factor frequencies as a function of the social composition of the population. The frequency of open defecation, backyard pig raising and pork consumption differed significantly (P < 0.005) among the different coexisting caste and ethnic groups. In the same survey, the taeniosis prevalence was examined among the different groups. Tapeworm carriers were identified at a high prevalence among the Dum, one of the most disadvantaged communities of Nepal. A PCR-RFLP assay revealed that all collected tapeworm specimens were T. asiatica, a species thus far not known to occur in South Asia. These results can help to understand the epidemiology of T. solium in Nepal, which appears to be more complex than thought so far.

Seasonal and biogeographical patterns of gastrointestinal parasites in large carnivores: wolves in a coastal archipelago

Parasites are increasingly recognized for their profound influences on individual, population and ecosystem health. We provide the first report of gastrointestinal parasites in gray wolves from the central and north coasts of British Columbia, Canada. Across 60 000 km2, wolf feces were collected from 34 packs in 2005–2008. At a smaller spatial scale (3300 km2), 8 packs were sampled in spring and autumn. Parasite eggs, larvae, and cysts were identified using standard flotation techniques and morphology. A subset of samples was analysed by PCR and sequencing to identify tapeworm eggs (n=9) andGiardiacysts (n=14). We detected ⩾14 parasite taxa in 1558 fecal samples.Sarcocystissporocysts occurred most frequently in feces (43·7%), followed by taeniid eggs (23·9%),Diphyllobothriumeggs (9·1%),Giardiacysts (6·8%),Toxocara caniseggs (2·1%), andCryptosporidiumoocysts (1·7%). Other parasites occurred in ⩽1% of feces. Genetic analyses revealedEchinococcus canadensisstrains G8 and G10,Taenia ovis krabbei, Diphyllobothrium nehonkaiense,andGiardia duodenalisassemblages A and B. Parasite prevalence differed between seasons and island/mainland sites. Patterns in parasite prevalence reflect seasonal and spatial resource use by wolves and wolf-salmon associations. These data provide a unique, extensive and solid baseline for monitoring parasite community structure in relation to environmental change.

The molecular epidemiology of parasite infections: tools and applications

Molecular epidemiology, broadly defined, is the application of molecular genetic techniques to the dynamics of disease in a population. In this review, we briefly describe molecular and analytical tools available for molecular epidemiological studies and then provide an overview of how they can be applied to better understand parasitic disease. A range of new molecular tools have been developed in recent years, allowing for the direct examination of parasites from clinical or environmental samples, and providing access to relatively cheap, rapid, high throughput molecular assays. At the same time, new analytical approaches, in particular those derived from coalescent theory, have been developed to provide more robust estimates of evolutionary processes and demographic parameters from multilocus, genotypic data. To date, the primary application of molecular epidemiology has been to provide specific and sensitive identification of parasites and to resolve taxonomic issues, particularly at the species level and below. Population genetic studies have also been used to determine the extent of genetic diversity among populations of parasites and the degree to which this diversity is associated with different host cycles or epidemiologically important phenotypes. Many of these studies have also shed new light on transmission cycles of parasites, particularly the extent to which zoonotic transmission occurs, and on the prevalence and importance of mixed infections with different parasite species or intraspecific variants (polyparasitism). A major challenge, and one which is now being addressed by an increasing number of studies, is to find and utilize genetic markers for complex traits of epidemiological significance, such as drug resistance, zoonotic potential and virulence.

A review of parasitic zoonoses in a changing Southeast Asia

Parasitic zoonoses are common and widely distributed in the Southeast Asian region. However, the interactions between parasites, hosts and vectors are influenced by environmental, socio-cultural and livestock production changes that impact on the distribution, prevalence and severity of disease. In this review we provide an update on new knowledge in the context of ongoing changes for the food-borne pig associated zoonoses Taenia solium and Trichinella spp., the food-borne trematodes Opisthorchis viverrini and Clonorchis sinensis, the water-borne trematodes Schistosoma spp., the vector-borne zoonotic protozoa Plasmodium knowlesi and Leishmania spp. and the soil-borne zoonotic hookworm Ancylostoma ceylanicum. These various changes need to be considered when assessing or developing regional control programs or devising new research initiatives in a changing SE Asia.