Assessing the Viability and Degeneration of the Medically Important Filarial Nematodes

Abstract

The assessment of nematodes as they generate and die is not a simple thing to do due in part to the complexity of the organism, and the fact that still relatively little is known about their physiology and internal biology. Indeed, the pathological changes in the internal organs of the worms are still only recognized in general terms. Obviously dead worms are easily recognized (when fractured, or calcified, etc.) but the lesser obvious changes can be difficult to detect and interpret. The point at which a worm can be defined as dead is not a simple matter; cessation of motility is currently the most commonly used parameter for this but it is not always a robust indicator and better indicators are needed. Various methods can be used to assess the presence, viability, and functionality of nematodes but these must be used with an understanding of the situation at hand and the specific questions being addressed. Careful use of appropriate statistics is essential given the complex nature of the target organism and the variability in the changes that can be seen within even one anatomical component of these worms. Histological assessment of the parasites present in both parasitized host tissues and isolated worms used in in vitro experiments can provide information that gives a more detailed understanding of the changes in nematodes as they degenerate and die. Understanding of the pathways nematodes follows as they degenerate naturally or under various external pressures, such as chemotherapy, remains a fascinating and potentially productive goal for investigation. Likewise, a complete understanding and definition of specific indicators that reflect parasite load, parasite viability, and damage, or reduced fecundity, will greatly help the fight against those nematode infections that currently cause significant burdens of disease in humans and animals.

Macrofilaricidal efficacy of single and repeated oral and subcutaneous doses of flubendazole in Litomosoides sigmodontis infected jirds

“…For histological assessment of the remaining female adult worms, one randomly selected intact individual worm per jird, if present, was selected and worms were processed for sectioning by embedding in HistoGel (Thermo Scientific Richard-Allan Scientific—American MasterTech, Waltham, MA, US), an aqueous gel composition, as coiled entities and sectioned by standard histological section preparation procedures [34–36] they were stained by hematoxylin and eosin for assessment. Two major criteria were assessed: firstly, damage to the three major structures of the worm (i.e.…”

Investigating Flubendazole as an Anthelmintic Treatment for Guinea Worm (Dracunculus medinensis): Clinical Trials in Laboratory-Reared Ferrets and Domestic Dogs in Chad

“…The distinctive degenerative changes in uterine tissues and developing forms of the FBZ-exposed worms recovered from ferrets are consistent with the degenerative changes seen in other filarial nematodes exposed to FBZ. 15 , 20 The commonly seen dissolution and degeneration of the rapidly developing new morula stage is likely due to the tubule disassociating property of FBZ. The high degree of damage to the morula and other uterine stages induced by FBZ is thought to cause blockage of the uterus with the consequent death of the adult worm.…”

“… 19 Sections were fixed and stored in 10% formol (3.7% formaldehyde), then embedded using HistoGel specimen processing gel (Thermo Scientific, Waltham, MA) allowing for the production of transverse sections through the worm segments. 20 Sections were cut from three levels (∼100 μm apart) of each worm segment and stained with hematoxylin and eosin. Each section was first assessed for histological integrity before scoring for any damage or degeneration in any of the major anatomic components of worms, including uterine contents.…”

Understanding the Pathogenesis of the Major Human Filarial Nematode Infections

“…Observations in the bovine equivalent of human OV, Onchocerca gutturosa, where the female adult worms lie in a serpentine fashion in the epi-ligament membranes lining the nuchal ligament in cattle-the only cellular reactions associated with the live adult worms are again lymphoid cellular aggregates; however, in this case these are located adjacent to the vaginal opening of the female worms suggesting that material emerging from the worms's uterus (which maybe be uterine fluids, microfilariae or microfilarial components) are involved in the induction of this host response. The second major form of observable tissue response to adult worms is that associated with degenerating, or essentially non-viable, adult worms; it should be noted that the definition of nematode viability, and indeed the definition of a live versus a dead filarial worm, is controversial [5]. The cellular responses to degenerating adult filaria is characterised by the typically components of a chronic inflammatory response-e.g., macrophages of different morphologies, and in these cases, eosinophil leucocytes; this is parallel to a classical "foreign body" response in pathological terms.…”