Emerging parasite zoonoses associated with water and food

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

Systematics and epidemiology of trichinella.

Infectivity, persistence, and antibody response to domestic and sylvatic Trichinella spp. in experimentally infected pigs.

hyperoxia greatly reduces the incidence of phenytoin-induced cleft lip and palate in A/J mice. Science 212: 671–672 10. Moerman P, Fryns J P, Goddeeris P, Lauweryns J M, van Assche A 1983 Aberrant twinning (diprosopus) associated with anencephaly. Clinical Genetics 24: 252–256 11. Ramadan R O 1996 A dicephalic goat with other defects. Zentralblatt fur Veterinarmedizin Reihe A 43: 337–343 12. Saini S S, Khehra R S, Kwatra M S 1993 A diprosopus in a domestic chicken embryo. Avian Diseases 37: 898–899 13. Tiessen R G, van Elsacker-Niele A M, Vermeij-Keers C, Oepkes D, van Roosmalen J, Gorsira M C 1994 A fetus with a parvovirus B19 infection and congenital anomalies. Prenatal Diagnosis 14: 173–176 14. Verdi G D, Hersh J H, Russell L J 1991 Partial duplication of the face: case report and review. Plastic and Reconstructive Surgery 87: 759–762 15. Wei X, Sulik K K 1993 Pathogenesis of craniofacial and body wall malformations induced by ochratoxin A in mice. American Journal of Medical Genetics 47: 862–871 16. Yoneda T, Pratt R M 1982 Vitamin B6 reduces cortisone-induced cleft palate in the mouse. Teratology 26: 255–258

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WHO/FAO/OIE guidelines for the surveillance, prevention and control of taeniosis/cysticercosis

L'utilisation de tests serologiques pour le diagnostic de l'infection a Trichinella chez les animaux domestiques et sauvages et chez l'homme n'a pas ete standardisee juqu'a present. Cette revue fournit un ensemble de recommandations pour le developpement et l'utilisation de tests serologiques pour detecter les anticorps circulants dans les echantillons de serum. Les recommandations sont basees sur les meilleures informations scientifiques publiees et sur des donnees non publiees issues des laboratoires qui possedent une grande experience dans ce domaine. Elles representent la position officielle de la Commission internationale sur la trichinellose a propos des methodes acceptables et de l'evaluation de leur specificite et sensibilite. Ces recommandations sont susceptibles d'etre modifiees en fonction de nouvelles donnees scientifiques.

International Commission on Trichinellosis: recommendations on the use of serological tests for the detection of Trichinella infection in animals and man.

Taenia saginata infections were established in four groups of calves by administering doses of 10, 10(2), 10(3) and 10(4) infective eggs respectively by gavage. A fifth group remained as uninfected controls. Sera were collected from all calves over a period of 210 days. The sera were examined by an enzyme-linked immunosorbent assay (ELISA) with a fraction of larval Taenia hydatigena cyst fluid as antigen for the presence of anti-T. saginata IgG antibodies. At slaughter, the tongue, masseter, diaphragm and cardiac muscles and liver were examined for cysticerci. The higher dose rates of T. saginata eggs were reflected in higher numbers of cysticerci found in the calves at necropsy. There was also a correlation between higher levels of antibodies produced as measured by the ELISA and the numbers of eggs given. Sero-conversion was first detected about 25 days postinfection in heavy infections and later in the lighter infections. Maximal levels of antibody occurred between 40 and 60 days postinfection, followed by a gradual decrease in levels of antibody. A secondary increase in antibody occurred between 160 and 200 days postinfection which might have been due to release of antigen after death of the cysticerci. The low level of circulating antibodies in light infections may result in false positive or false negative diagnoses depending upon the selection of the cut-off point.

Serological diagnosis of cysticercosis by an enzyme-linked immunosorbent assay in experimentally infected cattle.

Trichinella spiralis spiralis infections were established in cattle by gavage and by feeding infected musculature in the ration. Trichinae were present in greatest numbers in masseter, tongue and diaphragm. Trichinella spiralis nativa had a low infectivity to cattle although a light infection was established in one cow by a heavy challenge. Cattle had an aversion to eating musculature unless it was camouflaged with molasses. Clinical signs of reluctance to eat and masticate were observed between 10 and 30 days postinfection. Eosinophil counts started to increase at seven days and peaked at about 30 days postinfection. By day 60 eosinophil counts returned to near preinfection levels but in animals examined greater than 90 days postinfection, the counts were variable. Focal lesions of eosinophilic myositis were observed up to about 90 days postinfection. Little cellular reaction was observed surrounding trichinae after muscle invasion and cyst development was completed except for cysts undergoing disintegration. Seroconversion occurred in all cattle examined between 7 and 14 days postinfection. Seroconversion was associated with IgG1 and IgG2 immunoglobulins. Peak levels of antibody occurred between 30 and 60 days. Cattle examined at 182 and 369 days postinfection showed a gradual decrease in antibody levels over time.

Pathogenesis and serodiagnosis of experimental Trichinella spiralis spiralis and Trichinella spiralis nativa infections in cattle.

Enzyme immunoassays using the triple antibody enzyme linked immunosorbent assay (ELISA) with both Trichinella spiralis spiralis and T. spiralis nativa excretory-secretory (ES) antigens and a commercial Trichinella spiralis enzyme immunoassay test kit were carried out on sera from pigs that were infected with light, moderate and high doses of infective T. spiralis spiralis and T. spiralis nativa respectively. Seroconversion occurred in all pigs given infective Trichinella larvae although no trichinae were recovered from pigs given T. spiralis nativa larvae and examined between days 92 and 99 postinfection by pepsin digestion. Anti-Trichinella antibodies were detected in pigs infected with T. spiralis spiralis and T. spiralis nativa by ELISA using either the homologous or heterologous ES antigen. The commercial Trichinella spiralis enzyme immunoassay test kit also detected anti-Trichinella antibodies in both the T. spiralis spiralis and T. spiralis nativa infected pigs. The commercial test kit did not appear to be as sensitive as the triple antibody ELISA since it usually took two to three days longer for seroconversion to be detected by the former procedure. Finally seroconversion occurred more rapidly in swine infected with T. spiralis spiralis than with pigs receiving comparable doses of T. spiralis nativa.

Comparative assessment of a double antibody enzyme immunoassay test kit and a triple antibody enzyme immunoassay for the diagnosis of Trichinella spiralis spiralis and Trichinella spiralis nativa infections in swine.

Trichinella spiralis spiralis infections were established in sheep by administering infective larvae via gavage or feeding infected musculature. Trichinella spiralis nativa infective larvae had a low infectivity for sheep although light infections may be established in some animals with large infective doses. For the most part, sheep were averse to ingesting musculature mixed in a grain ration unless it was camouflaged with molasses. The heaviest infections usually occurred in the masseter muscle. The fact that sheep are averse to ingesting muscle tissue may reduce the likelihood of trichinosis. Anti-Trichinella antibodies to both T: spiralis spiralis and T. spiralis nativa were produced as demonstrated by the enzyme-linked immunosorbent assay. Seroconversion occurred in several sheep challenged with T. spiralis nativa even though larvae were not recovered from the musculature by pepsin-digestion.

Experimental trichinosis in sheep.

Light Trichinella infections were established in three ponies given 1000, 5000 and 25000 T. spiralis spiralis infective larvae respectively by stomach tube. A predilection site of infection in all ponies was the tongue. Anti-Trichinella antibodies were detected in all ponies by the enzyme-linked immunosorbent assay using a T. spiralis spiralis excretory-secretory antigen. The ponies given 5000 and 25000 infective larvae reacted positively on days 26 and 24 postinfection, respectively, using a criterion of greater than or equal to 5 X mean optical density readings of preinfection sera as positive. The pony given 1000 larvae did not react positively although antibodies were present as indicated by 3 X to 4 X mean optical density readings of preinfection sera. The results of this limited study indicate that the enzyme-linked immunosorbent assay cannot be used to certify horsemeat free of Trichinella since the presence of detectable antibody levels appears to be related to the magnitude of the infection and duration of the infection when the animal is tested.

H J Smith

Papers

Serological diagnosis of cysticercosis by an enzyme-linked immunosorbent assay in experimentally infected cattle.

Pathogenesis and serodiagnosis of experimental Trichinella spiralis spiralis and Trichinella spiralis nativa infections in cattle.

Comparative assessment of a double antibody enzyme immunoassay test kit and a triple antibody enzyme immunoassay for the diagnosis of Trichinella spiralis spiralis and Trichinella spiralis nativa infections in swine.

Experimental trichinosis in sheep.

Experimental Trichinella infections in ponies.