Contributor: Emeritus Professor John Goldsmid, University of Tasmania
This patient was admitted to a hospital in Tasmania suffering from dysarthria and an inability to stand. He was placed in ICU due to severe breathing problems. His medical records revealed that for a number of years, he had been investigated for a "mild reactive hepatitis" with a slight eosinophilia – believed to be due to a drug reaction or a resolving hepatitis. Subsequently, he had developed problems with wasting and muscle weakness. The clinical diagnosis was polymyositis – a diagnosis which seemed to be confirmed by a muscle biopsy. Again, an eosinophilia was noted. Based on these findings, a diagnosis of autoimmune polymyositis was made and the patient treated with prednisolone. His deteriorating condition accelerated, resulting in his current hospital admission. A further muscle biopsy at this stage was taken and microscopic examination of teased muscle fibres (Figs 3.1-3.3) and histological sections showed the presence of numerous live nematodes within the muscle fibres (Figs 3.4, 3.5). A careful history from the patient revealed that he was a keen hunter and had frequently eaten wallaby patties, often undercooked.
Teased out muscle fibres showing live worms
Live worm from muscle: saline mount (low power)
Worm teased from muscle: saline mount (high power)
Histological section of muscle with adult nematode
Histological section of muscle to show intrafibrillar worms
What is your diagnosis?
Native marsupials in Tasmania, especially scavengers such as Tasmanian Devils and Quolls, were found by Obendorf et al (1990) to be widely infected with Trichinella pseudospiralis. The diagnosis in New Zealand, of this nematode in a biologist who had worked with Tasmanian Devils and who had consumed a wallaby stew while in Tasmania (Andrews et al, 1994) led to an initial suspected diagnosis of T. pseudospiralis in the present case. However, on careful examination of the worms dissected from the muscle, it can be seen that various stages of development are present – juveniles and adults (Figs 1-4). Further, the worms are sited within the muscle fibrils (Fig. 5) – all features not shown by trichina worms. Additionally, subsequent serology for Trichinella proved negative (Dunnett et al, 1998). Subsequently, the worms were identified by Spratt et al (1999) as a new genus and species of muspeceoid nematode and named Haycocknema perplexum. It is interesting to note that re-examination of the original T. pseudospiralis case diagnosed in New Zealand, led Andrews et al (1997) to conclude that their case had been infected with both T. pseudospiralis and H. perplexum! The present patient was treated, initially with mebendazole and then with albendazole, and made a good recovery. It would seem that the patient had become infected with the nematode and that the treatment with prednisolone for the initial diagnosis of autoimmune myositis, had allowed the worms to multiply rapidly, resulting in the patient’s deteriorating condition. Subsequently, another three cases of haycocknematosis presenting as a myositis have been diagnosed in humans but this time from North Queensland as reviewed by (Basurry et al, 2008).
Although the natural hosts and mode of transmission of H. perplexum remain unknown, the history of eating wallaby meat and the co-infection in one case of H. perplexum with T. pseudospiralis, suggests that infection may have been by oral ingestion of undercooked meat. This, however, remains to be established, but it does suggest that adequate cooking of marsupial meat is desirable not only for prevention of infection with Trichinella pseudospiralis and maybe Haycocknema, but also of Toxoplasma gondii (Robson and Wood, 1995) as discussed by Goldsmid, Speare and Bettiol, 2003).