Behaviour of filariae: morphological and anatomical signatures of their life style within the arthropod and vertebrate hosts

Abstract

This paper attempts to pinpoint the most original morphological anatomical features of the biology of filariae per se and those which are or could be important for triggering regulatory processes in the arthropod vector and uncontrolled pathogenic processes in the vertebrate hosts. The following stages are considered: the motile egg or newly-hatched larva, the microfilaria, in the lymphatic or blood vessels of its vertebrate host; the larva, its migrations and its intrasyncitial development in the hematophagous arthropod subverted as vector; its transfer to the vertebrate host, migratory properties through the lymphatic system, maturation, mating and, finally, egg laying in the tissues they reach. This synthesis is based on parasite morphological features and their functional interpretation, histological features in the different niches the filariae reach, and on quantitative analyses of filarial development at its different phases, as well as on the rare and valuable observations of living parasites in situ. Data have been drawn from various species of Onchocercidae from amphibians, reptiles, birds and mammals. These comparative analyses have revealed the major constraints to which the filariae, including those parasitizing humans, have been subjected during their evolution from their ancestors, the oviparous and heteroxenic spirurids. Emphasis is placed on mechanical events: resistance of the microfilariae to the currents in the blood or lymph vessels, regulatory processes induced in the vector mesenteron by the movements of the ingested microfilariae, transient disruption by the microfilarial cephalic hook of the vectors' tissues and cell membranes during microfilarial translocation, attachment of males to females during mating by means of 'non-slip' systems, etc. Like other nematodes, filariae are equipped with sensory organs and a locomotor system, composed of the muscles and of the original osmoregulatory-excretory cell. Any change in one of these elements will result in the destruction of the filaria, at some stage of its development. In the vertebrate host, the intravascular stages will no longer be able to resist being carried passively towards the organs of destruction such as the lymph nodes or the lungs.

Neutropenic Mice Provide Insight into the Role of Skin-Infiltrating Neutrophils in the Host Protective Immunity against Filarial Infective Larvae

“…e . about 750 μm) [ 58 , 60 ] we sought to investigate the potential of neutrophils in inducing NETs that can be released by in response to microbe size-sensing [ 61 ]. The NETs were reported to capture Gram-positive and Gram-negative bacteria, fungi, and viruses [ 62 – 64 ] as well as Apicomplexa parasites, Leishmania , Eimeria , Plasmodium , and Toxoplasma [ 65 ] and the Strongyloides stercoralis nematode [ 66 ].…”

Differential tissular distribution ofLitomosoides sigmodontismicrofilariae between microfilaremic and amicrofilaremic mice following experimental infection

“…Depending on the species, the filarial nematodes causing the diseases are located in various host tissues, e.g. lymphatic vessels, connective tissues or coelomic cavities (Bain & Babayan, 2003; Bain et al , 1994). There, they mature and release microfilariae, which circulate either in the bloodstream for some species or in the dermis for others (Bain & Babayan, 2003).…”

“…lymphatic vessels, connective tissues or coelomic cavities (Bain & Babayan, 2003; Bain et al , 1994). There, they mature and release microfilariae, which circulate either in the bloodstream for some species or in the dermis for others (Bain & Babayan, 2003). Microfilariae are a major cause of pathogenesis, and their circulation in the peripheral blood or in the dermis, where they can be ingested by their vector, is essential for transmission (Hoerauf et al , 2005; Bain et al , 1994; Aimard et al , 1993, Bockarie et al , 2009).…”

A lymphatic dwelling filarioid nematode, Rumenfilaria andersoni (Filarioidea; Splendidofilariinae), is an emerging parasite in Finnish cervids

“…Microfilarial periodicity among filaroids has developed so that peak microfilaraemia coincides with the active feeding period of the insect vector. Thus, the behaviour and niches of mf have been selected under the pressure and selective regime established by feeding and activity habits of specific hematophagous insects [ 31 ]. The peak microfilaremia of R. andersoni during summer midnights perhaps suggests that night active mosquitoes such as species of Culiseta and Anopheles are required for development and transmission.…”