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The Parasitic Protozoa and Helminth Worms
Published in Julius P. Kreier, Infection, Resistance, and Immunity, 2022
Trichinosis is caused by infection with the nematode worm, Trichinella spiralis. The adult worms, which can infect virtually any carnivorous mammal, are quite small, about 1.5 mm by 0.04 mm for the male, and 3.5 mm by 0.06 mm for the female. The life cycle is simple with the same individual serving as both the intermediate host and definitive host. When infected muscle (containing encysted larvae) is ingested, the larvae are released in the small intestine and invade the mucosa where the worms mature. The females then migrate deeper into the mucosa to deposit larvae that gain access to the lymphatics and the blood. The larvae burrow into the fibers of striated muscle and then encyst (Figure 17.8). The symptoms produced depend on the number of worms ingested and may occur in phases corresponding to the periods of intestinal invasion, migration of larvae, and encystment in muscle. Clinical findings usually consist of diarrhea, muscle pain, fever, weakness, and eosinophilia, and death may result In severe infections. As for most other nematode infections, the mechanisms involved in immunity to T. spiralis in humans is unclear. The migrating larvae secrete a number of antigens that elicit both cellular and antibody responses, and some of these are responsible for the formation of granulomas, consisting of macrophages, lymphocytes, eosinophils, and neutrophils that eventually encapsulate the worm. Adult worms in the gut may be affected by IgE-mediated changes in gut physiology that result in the dislodgement of the worms but not in their death.
Control of Human Intestinal Nematode Infections
Published in Max J. Miller, E. J. Love, Parasitic Diseases: Treatment and Control, 2020
Nematode infections of low intensity are unlikely to produce symptoms, and a carrier state is common. High worm burden, on the other hand, may cause significant morbidity and economic losses to individual persons and to whole communities.2 This is especially the case in undernourished populations, where even light infections may be detrimental to the health of the host, particularly regarding absorption of nutrients, growth, and resistance to infection. Abdominal pain, diarrhea, blood loss, anal pruritis, malabsorption, and occlusion are the intestinal symptoms of cardinal importance. The main extraintestinal features of intestinal worm infections are skin lesions, anemia, immunological disturbances, obstructions, and malnutrition. Physicians concerned with medical parasitology should learn from the veterinary and farming professions, where there is much more positive interest in diseases caused by parasites, possibly because the ill effects are more easily quantified and measured and because of their economic importance.3
Pulmonary Dogworm (Dirofilaria immitis) Infection Presenting as a Solitary Pulmonary Nodule
Published in Wickii T. Vigneswaran, Thoracic Surgery, 2019
Pulmonary nematode infections are well-known entities and have been reported from all parts of the world. There are different varieties of worms that cause pulmonary infections, with some being more common than others depending on endemic nature of the parasite. Pulmonary dirofilariasis is a rare zoonotic nematode infection that can be mistaken for a malignant neoplasm. We describe a rare case of a patient with Dirofilaria immitis (D. immitis) in the lung presenting as a solid nodule.
The relevance of studying insect–nematode interactions for human disease
Published in Pathogens and Global Health, 2022
Zorada Swart, Tuan A. Duong, Brenda D. Wingfield, Alisa Postma, Bernard Slippers
Both VPN and EPN suppress the immune responses of their host [38,41]. As VPN and EPN are closely related phylogenetically [73,74], orthologues of genes associated with host immunosuppression can be found in both types of nematodes [30]. Insect-pathogenic Heterorhabditis bacteriophora shares ancestral traits with free-living C. elegans but is phylogenetically positioned closer to the mammal-parasitic nematodes. Heterorhabditis bacteriophora, therefore, represents a ‘bridge’ species to translate existing knowledge of molecular pathways in C. elegans and other EPN, to VPN [73]. Compared to mammalian parasites, EPN culturing requires fewer resources in terms of laboratory equipment and personal protection, as well as host animals. As a result, entomopathogenic nematodes and their insect hosts offer an alternative option to study nematode infections in humans and other mammals.
Overcoming challenges in the diagnosis and treatment of parasitic infectious diseases in migrants
Published in Expert Review of Anti-infective Therapy, 2020
Francesca F. Norman, Belen Comeche, Sandra Chamorro, Rogelio López-Vélez
Serological assays appear to be the most effective screening tests for detection of infection in settings of low endemicity due to their higher sensitivity when compared with conventional parasitological methods [110]. Parasitological methods to detect larvae of S. stercoralis in stool (such as agar plate culture and Baermann methods) have limited sensitivity although a combination of both serological and parasitological techniques may improve sensitivity considerably. Parasitological methods are time-consuming, require skilled personnel, and are therefore not usually considered as the first option for public health screening [2]. Limitations of serological tests include lower sensitivities in immunosuppressed patients (if possible, these should be performed prior to initiation of immune suppression), the inability to distinguish between past and current infections and the cross-reactivity with other nematode infections. Stool nucleic acid amplification tests (using PCR or loop-mediated amplification LAMP assays) have become increasingly available although low-grade production of larvae and the presence of PCR inhibitors in stools may limit the sole use of these techniques for diagnosis [109,111,112]. Direct antigen detection tests in stool are currently being evaluated and may become useful screening tools in future [111].
Oxfendazole: a promising agent for the treatment and control of helminth infections in humans
Published in Expert Review of Anti-infective Therapy, 2019
Armando E. Gonzalez, Ellen E. Codd, John Horton, Hector H. Garcia, Robert H. Gilman
The pharmacokinetics, safety, and broad spectrum of activity of oxfendazole have consistently been demonstrated in intestinal helminth infections of animals as well as in tissue dwelling larval cestodes (Taenia solium cysticercosis, echinococcosis, T. hydatigena), trematode (fasciolasis), and filarial infections in a wide range of animal models. Whilst animal models are an indication of potential activity in similar human infections, translating this information into human therapies is a significant challenge since the pharmacokinetics and metabolism are often very different. Thus, with each human infection it will be necessary to conduct specific studies to determine effective doses before moving into larger scale studies to register the product. For example, while OXF has been shown to be very effective in porcine cysticercosis, allowing single-dose treatment, the long half-life of OXF and ability to penetrate the brain parenchyma may not be seen with human infections. Similarly, when considering human intestinal nematode infections, it is not possible to directly associate effective doses in domestic species and it will be necessary to undertake dose ranging studies to determine regimens that are effective against the whole range of intestinal nematodes. One of the challenges is therefore to determine the infecting helminth species most likely to be amenable to treatment and to develop this first as a priority. This will in the longer term provide additional safety data to support further study in other infections.