Focus of human trichinellosis in Papua New Guinea

From wildlife to humans: The global distribution of Trichinella species and genotypes in wildlife and wildlife-associated human trichinellosis

Zoonotic nematodes of the genus Trichinella are foodborne parasites that have a global distribution in wild carnivores and omnivores, with spillover and spillback into domestic livestock and people, with concomitant trade and health consequences. Historically, most human cases were linked to domestic pigs infected with Trichinella spiralis, but under current high biosecurity swine production in many countries, wildlife have become a more important source of human trichinellosis. The aim of this review is to update the global distribution of Trichinella species and genotypes reported in wildlife, as well as reported human outbreaks from the consumption of wildlife. Using several online databases and by "snowballing" references, hundreds of reports of Trichinella spp. in wildlife published between January 1991 and December 2023 provide an important update to the host and geographic range for each of the recognized 13 species/genotypes, grouped by continent. Surveillance effort was highest in Europe and North America, while Africa, Asia, Central and South America have had limited surveillance, in some instances with human cases serving as sentinels of transmission in a region. Dozens of human outbreaks are described, with wild boars (Sus scrofa) being the most frequently implicated wildlife species in human outbreaks globally. Bears are an important source of infection in North America, for wildlife tourism, and importation of bear meat has also been implicated in multicountry outbreaks. The largest study limitation was the dearth of molecular identification of larvae in both wildlife surveillance studies and human outbreaks, particulary in under-studied regions. We highlight the need for enhanced molecular epidemiological approaches to outbreaks of this important foodborne parasite, and emphasize the need for a One Health approach to manage Trichinella spp. which transmit among terrestrial and marine wildlife (including migratory birds), pigs, horses, and people, often across large geographic scales and borders.

The genus Trichinella and its presence in wildlife worldwide: A review

The genus Trichinella has a worldwide distribution, infecting people, domestic animals, and wildlife. It includes 13 genotypes, which are geographically delimited; Trichinella is transmitted to people through the ingestion of undercooked meat. Historically, it has been associated with pigs, but most Trichinella species affect wildlife, and cases of trichinellosis due to the consumption of game meat have been emerging. Therefore, it is important to monitor the sources of transmission to domestic animals and humans. The objective of this work was to analyse reports of Trichinella spp. in wild/feral animals around the world to identify the needs of future research in the epidemiology of the sylvatic cycle. A search of studies published until 2021 was conducted using Web of Science and SciELO. In the Palearctic, the most commonly studied hosts were wild boars and red foxes, and hosts with the highest prevalence rates were polar bears and martens. In the Nearctic, red foxes and black bears were the most frequently studied hosts, and the highest prevalence was found for wolverines and brown bears. In the Neotropics, positive reports were only identified in two countries, with wild boars being the most commonly studied species, and armadillos featuring the highest prevalence. In the Afrotropics, Trichinella limits its presence to Sub-Saharan Africa, where lions are the most studied hosts, and spotted hyenas have the highest prevalence. In the Indo-Malaya and Australasia ecozones, information on wildlife is scarce; the Norwegian rat is the most frequently studied host, and the Tasmanian devil has the highest prevalence of infection. In the last decade, research on world wildlife has increased which is associated with more frequent trichinellosis outbreaks caused by the consumption of wild meat. The results suggest the need to increase research in developing countries, particularly where more diverse sources of meat are available for human consumption.

Glycan microarray profiling of parasite infection sera identifies the LDNF glycan as a potential antigen for serodiagnosis of trichinellosis

Diagnostic methods for parasite infections still highly depend on the identification of the parasites by direct methods such as microscopic examination of blood, stool and tissue biopsies. Serodiagnosis is often carried out to complement the direct methods; however, few synthetic antigens with sufficient sensitivity and specificity are available. Here we evaluated a glycan microarray approach to select for synthetic glycan antigens that could be used for serodiagnosis of parasitic infections. Using a glycan array containing over 250 different glycan antigens, we identified GalNAcβ1-4(Fucα1-3)GlcNAc-R (LDNF) as a glycan antigen that is recognized by antibodies from Trichinella-infected individuals. We synthesized a neoglycoconjugate, consisting of five LDNF molecules covalently coupled to bovine serum albumin (BSA), and used this neoglycoconjugate as an antigen to develop a highly sensitive total-Ig ELISA for serological screening of trichinellosis. The results indicate that glycan microarrays constitute a promising technology for fast and specific identification of parasite glycan antigens to improve serodiagnosis of different parasitic infections, either using an ELISA format, or parasite-specific glycan arrays.

Validation of an enzyme-linked immunosorbent assay for diagnosis of human trichinellosis

Trichinellosis is a zoonotic disease caused by the consumption of raw or semiraw meat from different animals harboring Trichinella larvae in their muscles. Since there are no pathognomonic signs, diagnosis can be difficult; for this reason, serology is important. The objective of this study was to validate an enzyme-linked immunosorbent assay (ELISA) using excretory/secretory antigens to detect anti-Trichinella immunoglobulin G antibodies in human sera. A total of 3,505 human serum samples were tested. A receiver-operator characteristic (ROC) curve analysis was performed. The accuracy of the test was determined by calculating the area under the curve, which was equal to 0.999, indicating high accuracy. The coefficient of variation calculated for data from four serum samples in eight working sessions was no higher than 5% for the positive sera or 14% for the negative sera. Moreover, the analysis of the differences in optical density between duplicates indicated a high repeatability for the ELISA. At the ROC optimized cutoff, the sensitivity and specificity of the test were, respectively, 99.2% and 90.6% (specificity of 95.6% when excluding the samples from multiparasitized persons from Tanzania). The validated ELISA showed good performance in terms of sensitivity, repeatability, and reproducibility, whereas the specificity was limited. These results suggest that this test is suitable for detecting anti-Trichinella antibodies in human sera for diagnostic purposes, whereas its use in epidemiological surveys could be questionable.

Parasitic zoonoses in Papua New Guinea

Relatively few species of zoonotic parasites have been recorded in humans in Papua New Guinea. A greater number of potentially zoonotic species, mostly nematodes, occur in animals but are yet to be reported from humans. Protozoa is the best represented group of those infecting man, withGiardia duodenalis,Cryptosporidium parvum,Cyclospora cayetanesis,Toxoplasma gondii,Sarcocystisspp.,Entamoeba polecki,Balantidium coliand, possibly,Blastocystis hominis. The only zoonotic helminths infecting humans include the trematodeParagonimus westermani, the cestodesHymenolepis nana,H. diminutaand the sparganum larva ofSpirometra erinacea, and the nematodesTrichinella papuaeandAngiostrongylus cantonensisand, possibly,Ascaris suum. Other groups represented are Acanthocephala (Macracanthorhynchus hirudinaceus)), insects (Chrysomya bezziana,Cimexsp.,Ctenocephalidesspp.), and mites (Leptotrombidiumspp. and, possiblySarcoptes scabiei, andDemodexsp.). One leech (Phytobdella lineata) may also be considered as being zoonotic. The paucity of zoonotic parasite species can be attributed to long historical isolation of the island of New Guinea and its people, and the absence until recent times of large placental mammals other than pig and dog. Some zoonotic helminths have entered the country with recent importation of domestic animals, in spite of quarantine regulations, and a few more (two cestodes, one nematode and one tick) are poised to enter from neighbouring countries, given the opportunity. Improvement in water supplies, human hygiene and sanitation would reduce the prevalence of many of these parasites, and thorough cooking of meat would lessen the risk of infection by some others.

Systematics and epidemiology of trichinella

In this review, we describe the current knowledge on the systematics, ecology and epidemiology of Trichinella and trichinellosis, and the impact of recent research discoveries on the understanding of this zoonosis. The epidemiology of this zoonosis has experienced important changes over the past two decades, especially with regard to the importance of the sylvatic cycle and the sylvatic species. Outbreaks of trichinellosis due to Trichinella spiralis from domestic swine, while still frequent, increasingly are caused by other Trichinella spp. infecting hosts such as horses, dogs, wild boars, bears and walruses. The latter revelations have occurred as a result of a series of discoveries on the systematics of Trichinella spp., facilitated by new molecular tools. As a consequence, the genus is now composed of two clades, an encapsulated group (five species and three genotypes) and a non-encapsulated one (three species). This has sparked renewed investigations on the host range of these parasites and their epidemiological features. Most dramatic, perhaps, is the recognition that reptiles may also serve as hosts for certain species. This new knowledge base, in addition to having an important relevance for food safety policies and protection measures, is raising important questions on the phylogeny of Trichinella spp., the ecological characteristics of the species and their geographic histories. Answers to these questions may have great value for the understanding of the evolutionary biology for other parasitic helminths, and may increase the value of this genus as models for research on parasitism in general.

Prevalence of antibodies against A and B influenza viruses in South-Western Papua New Guinea

Influenza viruses remain a major cause of respiratory disease in both developed and developing countries. Nevertheless, there is little information on the prevalence of this respiratory infection in many developing countries, such as Papua New Guinea, since most of the available data originate from studies carried out in industrialized countries. In the present study, a serosurvey among residents of 47 remote villages of Papua New Guinea was conducted to evaluate the intensity of exposure to human influenza A and B viruses. The data obtained confirm the co-circulation of these antigenic variants, reported having circulated in the Southern Hemisphere. Variations in seroprevalence of influenza A and B virus infection were found within the study area.

Current status of Taenia solium and cysticercosis in Papua New Guinea

There is no evidence that taeniasis due to Taenia solium is present in Papua New Guinea (PNG), but there is some serological evidence that human cysticercosis exists at particular locations near the border with West Papua (Indonesia), where refugees from across the border have been settled. Only a few surveys have been conducted; the first was in 1986, when one refugee who originated from an infected locality in West Papua was found to be serologically positive, but asymptomatic. Subsequently, there have been unpublished reports of more positive but asymptomatic cases amongst refugees and, it is claimed, amongst local inhabitants that live near the border. A serological survey conducted in PNG in 1999 at the southern end of the border revealed no positive cases of cysticercosis. There are no reports of pigs or dogs affected with cysticercosis in PNG.

People, pigs and parasites in New Guinea: Relational contexts and epidemiological possibilities

Within Papua New Guinea the relationship people have with their pigs varies between societies. These differences arise in the earliest phase of rearing piglets and result in domestic animals whose primary attachments are to other pigs, to places or to people. For Papua New Guineans, different pig management regimes fulfill ecological and social needs. In addition, however, the ways in which pigs are raised and managed, and the presence or absence of a local population of wild pigs, have consequences for the exposure of both domestic pigs and people to parasites that they may host. Effective control of disease-inducing parasites should be attentive to society-specific relationships between people and their pigs.

Phylogenetic analysis of encapsulated and non-encapsulated Trichinella species by studying the 5S rDNA tandemly repeated intergenic region

The identification of sequence regions in the genomes of pathogens which can be useful to distinguish among species and genotypes, is of great importance for epidemiological, molecular, and phylogenetic studies. The 5S ribosomal DNA intergenic spacer region has been identified as a good target to distinguish among eight Trichinella species and genotypes. The recent discovery of two non-encapsulated species in this genus, Trichinella papuae and Trichinella zimbabwensis, which can infect both mammals and reptiles, has suggested analyzing their 5S rDNA. Amplification of the tandem repeats of the 5S rDNA intergenic region of encapsulated species of Trichinella shows a 751bp fragment, whereas the three non-encapsulated species show a fragment of 800bp with T. pseudospiralis showing an additional fragment of 522bp. Although the size of the 800bp PCR fragments of T. papuae and T. zimbabwensis are similar to that of T. pseudospiralis, there are differences in the 5S rDNA intergenic regions among the three non-encapsulated species. Phylogenetic analysis of the 5S rDNA intergenic regions shows a clustering together of the three non-encapsulated Trichinella species that is well separated from the encapsulated ones. In addition, a single PCR-based method allows distinguishing non-encapsulated and encapsulated species.

Trichinella infection in a hunting population of Papua New Guinea suggests an ancient relationship between Trichinella and human beings

A new Trichinella species, Trichinella papuae, was discovered in 11.5% of wild pigs in a remote region of Papua New Guinea. A survey was conducted to determine whether the inhabitants of this region are infected with Trichinella, as wild-pig meat represents their main source of protein. The prevalence of anti-Trichinella antibodies and its determinants were assessed among the inhabitants in 51 of the villages in the Morehead District of Papua New Guinea. We tested and interviewed 1536 people (28.8% of the adult population). Anti-Trichinella IgG were detected in 10.0% (95% Cl 8.5-11.6%) of them. The prevalence of seropositivity was higher in males (12.7%) than in females (7.5%) (P<0.01), and the seroprevalence significantly increased with age. In one area, seroprevalence was highest in villages nearest the hunting area in which wild pigs are infected with Trichinella papuae (P<0.01). Seropositivity was also correlated with the consumption of raw or undercooked meat. Persons reporting pain in the muscle joints and limbs were more likely to be seropositive; no severe clinical manifestations were observed. That infection was never severe suggests that the seropositive people are reinfected relatively often, but with very few larvae. If the epidemiological pattern of Trichinella infection observed among the hunting population of this area is any indication of the pattern of infection in prehistoric hunters, we can speculate that Trichinella infection due to the consumption of meat from wild animals was possibly a common disease among prehistoric populations.

Evaluation of Trichinella spiralis larva group 1 antigens for serodiagnosis of human trichinellosis

To identify Trichinella antigens suitable for high-specificity and high-sensitivity serodiagnosis of human trichinellosis, we evaluated assays using four antigens: (i) crude first-stage larval extract (CLE), (ii) O-deglycosylated CLE, (iii) tyvelose-bearing antigens (Trichinella spiralis larva group 1 [TSL-1] antigens) purified by US4 affinity chromatography and coupled directly to enzyme-linked immunosorbent assay (ELISA) plates (pTSL-1 antigens), and (iv) TSL-1 antigens immobilized on ELISA plates with the monoclonal antibody (MAb) US4 (cTSL-1 antigens). Assays using these antigens were compared by analysis of sera from healthy individuals (n = 224) (group 1), individuals with noninfectious intestinal pathologies (n = 114) (group 2), individuals with other parasitic infections (n = 107) (group 3), and individuals with confirmed trichinellosis (n = 42) (group 4). Our results indicate that capture ELISA using cTSL-1 antigens is the most effective method for serodiagnosis of human trichinellosis; this was the only method showing 100% specificity and 100% sensitivity at the patent stage of the infection, and it was also the most sensitive for sera obtained prior to patency in indirect immunofluorescence (IIF). Indirect ELISA with pTSL-1 antigens was also 100% specific but was slightly less sensitive, particularly with sera obtained before IIF patency. Inhibition ELISA with MAb US4 indicated (i) that in Trichinella-infected patients the immune response to TSL-1 antigens is directed mostly against tyvelose-containing epitopes (mean of 84.2% of total anti-TSL-1 immunoglobulin G1 [IgG1] antibody response [range, 51.3 to 97.6%]) and (ii) that in most individuals a large proportion of anti-CLE IgG1 antibodies (mean, 49.5%; range, 7.3 to 92.6%) are directed against tyvelose epitopes.

Inappropriate feeding practice favors the transmission of Trichinella papuae from wild pigs to saltwater crocodiles in Papua New Guinea

The recent discovery of Trichinella zimbabwensis in farmed crocodiles (Crocodilus niloticus) of Zimbabwe and its ability to infect mammals, and the development of both T. zimbabwensis and Trichinella papuae in experimentally infected reptiles led to an investigation of Trichinella infection in saltwater crocodiles (Crocodylus porosus) and in wild pigs (Sus scrofa) of Papua New Guinea, to see if T. papuae also, is present in both cold- and warm-blooded animals. Of 222 crocodiles examined, 47 animals (21.2%), all from Kikori, Gulf Province, were positive for non-encapsulated larvae in the muscles. The greatest number of larvae was found usually in the biceps, with an average of 7 larvae/g. One isolate from a crocodile infected successfully both laboratory rats and mice. Of 81 wild pigs examined, 9 from Bensbach river area (Western Province) and 1 from Kikori area (Gulf Province) were positive for non-encapsulated larvae in the muscles. Trichinella larvae from both saltwater crocodiles and wild pigs have been identified by multiplex-PCR analysis as T. papuae. The sequence analysis of the region within the large subunit ribosomal DNA, known as the expansion segment V, has shown the presence of a molecular marker distinguishing T. papuae isolates of Bensbach river area from those of Kikori area. This marker could be useful to trace back the geographical origin of the infected animal. The epidemiological investigation carried out in the Kikori area has shown that local people catch young crocodiles in the wild and keep them in holding pens for several months, before sending them to the crocodile farm in Lae (Morobe Province). They feed the crocodiles primarily with wild pig meat bought at the local market and also with fish. These results stress the importance of using artificial digestion for routinely screening of swine and crocodiles, and of adopting measures for preventing the spread of infection, such as the proper disposal of carcasses and the adequate freezing of meat.

Parasites and biosecurity--the example of Australia

Biosecurity issues as they impact on agriculture, health and the environment are becoming increasingly important. Surveillance is crucial in maintaining a country's biosecurity and this article looks at some of the issues in the context of Australia and its neighbors in the Asia-Pacific region, and emerging threats from parasitic diseases. The important threats to agriculture, public health and wildlife are highlighted, and attention is given to how future surveillance activities must be undertaken on a regional basis and involve neighboring countries if they are to be effective and lead to the protection of both the trade and health of the population.

New patterns of Trichinella infection

Human and animal trichinellosis should be considered as both an emerging and reemerging disease. The reemergence of the domestic cycle has been due to an increased prevalence of Trichinella spiralis, which has been primarily related to a breakdown of government veterinary services and state farms (e.g., in countries of the former USSR, Bulgaria, Romania), economic problems and war (e.g., in countries of the former Yugoslavia), resulting in a sharp increase in the occurrence of this infection in swine herds in the 1990s, with a prevalence of up to 50% in villages in Byelorussia, Croatia, Latvia, Lithuania, Romania, Russia, Serbia, and the Ukraine, among other countries. The prevalence has also increased following an increase in the number of small farms (Argentina, China, Mexico, etc.) and due to the general belief that trichinellosis was a problem only until the 1960s. The sylvatic cycle has been studied in depth at both the epidemiological and biological level, showing the existence of different etiological agents (Trichinella nativa, Trichinella britovi, Trichinella murrelli, Trichinella nelsoni) in different regions and the existence of "new" transmission patterns. Furthermore, the role of game animals as a source of infection for humans has greatly increased both in developed and developing countries (Bulgaria, Canada, Lithuania, some EU countries, Russia, USA, etc.). The new emerging patterns are related to non-encapsulated species of Trichinella (Trichinella pseudospiralis, Trichinella papuae, Trichinella sp.), infecting a wide spectrum of hosts (humans, mammals including marsupials, birds and crocodiles) and to encapsulated species (T. spiralis, T. britovi, and T. murrelli) infecting herbivores (mainly horses). The existence of non-encapsulated species infecting mammals, birds and crocodiles had probably remained unknown because of the difficulties in detecting larvae in muscle tissues and for the lack of knowledge on the role of birds and crocodiles as a reservoir of Trichinella. On the other hand, it is not known whether horse and crocodile infections existed in the past, and their occurrence has been related to improper human behavior in breeding. The problem of horse-meat trichinellosis is restricted to France and Italy, the only two countries where horse-meat is eaten raw, whereas mutton and beef have been found to be infected with Trichinella sp. only in China.