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The Parasite's Way of Life
Published in Eric S. Loker, Bruce V. Hofkin, Parasitology, 2023
Eric S. Loker, Bruce V. Hofkin
Many vector-borne parasites also come equipped with various adaptations designed to increase the odds of transmission. For instance, adult W. bancrofti females release microfilariae into the lymphatic fluid of the human host. From there, they enter the circulatory system. In doing so, they demonstrate a circadian rhythm, not unlike the schistosomes with which we opened this chapter. At night, when mosquito vectors are most likely to feed, microfilariae migrate to peripheral blood vessels near the skin, well positioned to be ingested along with a blood meal. The cues the microfilariae use are probably either changes in body temperature or in blood gas composition that occur at night, when the human host is sleeping. Where filarial worms are transmitted by day-biting mosquitoes, this pattern is reversed. Such periodicity may also be seasonal rather than only daily. The causative agent of canine heartworm Dirofilaria immitis also releases microfilariae into the blood of an infected dog. These larval nematodes, infective to the mosquito vector, increasingly localize in surface blood vessels in the spring just as mosquito numbers begin to increase.
Inflammatory, Hypersensitivity and Immune Lung Diseases, including Parasitic Diseases.
Published in Fred W Wright, Radiology of the Chest and Related Conditions, 2022
Dirofilaria immitis (the dog heart worm) is a nematode conveyed by mosquito type vectors, the parasite being found in Canada, the USA (especially the Eastern states and on the Pacific coast), Australia, etc., its distribution presumably being related to the presence of wild foxes, dogs, etc. A subcutaneous infection precedes microfilaraemia. In man the worms die and produce small ischaemic lung infarcts, which may have calcified centres. A serological diagnostic test is available. The first human case was reported by Dashiell (1961). Leonardi et al. (1977) noted 61 cases, Levinson et al. (1979) four cases, Larrieu et al. (1979) 48 cases and Chesney et al. (1983) one case. Cholankeril et al, (1983) showed by CT that the nodules lie subpleurally in the lung. Kido et al. (1991) reported a case in Japan causing a small peripheral left lower lobe mass (which was resected) and a small pleural effusion.
The Aedes Fauna: Different Aedes Species Inhabiting the Earth
Published in Jagriti Narang, Manika Khanuja, Small Bite, Big Threat, 2020
Annette Angel, Bennet Angel, Neelam Yadav, Jagriti Narang, Surender Singh Yadav, Vinod Joshi
Aedes triseriatus is known to be the primary vector for La Crosse virus and West Nile virus transmission (Barker et al., 2003; Berry et al., 1974; Borucki et al., 2002; Pantuwatana et al., 1974; Watts et al., 1974; Williams et al., 2007). Vertical transmission of the La Crosse virus has also been established (Miller et al., 1977; Tesh and Gubler, 1975; Watts et al., 1973). It has also been known to transmit Dirofilaria immitis (Liu et al., 2011). In vitro studies indicate its vectoral competence for viruses like yellow fever, Eastern encephalitis, Venezuelan encephalitis, and Western encephalitis.
Identification of potential vectors of Dirofilaria immitis and Brugia pahangi (Spirurida: Filariidae): First observation of infective third-stage larva of B. pahangi in Culex quinquefasciatus (Diptera: Culicidae)
Published in Pathogens and Global Health, 2022
Wei Yin Vinnie-Siow, Van Lun Low, Tiong Kai Tan, Meng Li Wong, Cherng Shii Leong, Nazni Wasi Ahmad, Yvonne Ai Lian Lim
Mosquito-borne filarioid nematodes such as Dirofilaria immitis and Brugia pahangi cause diseases to mammals, especially in domestic dogs and cats [1,2]. Dirofilaria immitis has a wide geographical distribution whereas B. pahangi is endemic in Southeast Asia (i.e. Malaysia, Thailand and Indonesia) [3,4]. Both parasites principally infect canine host, but the increasing reports of human filariosis highlight their potential as emerging zoonosis globally [2,5]. Transmission of filarioid parasites depends on the availability of microfilaraemic hosts, vectors, and favorable temperatures for the growth of the infectious stages in mosquitoes [6]. Mosquitoes of the genera Aedes, Culex, and Anopheles are the main vectors of filarioid parasites and they transmit L3 infective larvae of these parasites to potential hosts through their bites [7].
Development of a recombinant vaccine against human onchocerciasis
Published in Expert Review of Vaccines, 2021
David Abraham, John Graham-Brown, Darrick Carter, Sean A. Gray, Jessica A. Hess, Benjamin L. Makepeace, Sara Lustigman
Long the focus of efforts to alleviate morbidity and lost productivity, onchocerciasis has been identified by the World Health Organization as a potential candidate for global elimination through mass drug administration (MDA) of the donated drug ivermectin (IVM) (Mectizan®) [6–8]. This plan began in the 1990’s as the ‘Onchocerciasis Elimination in the Americas’ and later by the ‘African Programme for Onchocerciasis Control’ (APOC) in 1995 with a World Health Assembly goal to establish community-based sustainable treatments of 50 million people in 19 African countries having meso- and hyper-endemicity by 2010 [7,9]. In 2015, the mission of onchocerciasis elimination for Africa was passed from APOC to its successor, the Expanded Special Programme for the Elimination of Neglected Tropical Diseases [10]. Addition of vegetation ‘slash and clear’ for vector control, as a supplement to MDA, has been proposed as an adjunct to accelerate elimination of onchocerciasis [11]. However, numerous and formidable technical and logistical obstacles must still be overcome before the ambitious goal of elimination by 2030 can be achieved in Africa [9,12]. These include (1) MDA of IVM cannot be used in 11 Central African countries co-endemic with Loa loa infections due to the risk of severe adverse events [13–16]; (2) The few drugs active against the adult stage of the parasite are not used for MDA, and IVM, as well as the recently approved drug moxidectin, are only effective against microfilariae [17]; (3) The practical complication of treating people for 14 to 35 years compounds the difficulty of implementing the plan [7,8]; (4) Experimental studies indicate that susceptibility to reinfection may increase after treatment, further complicating the disruption of the transmission cycle [18–20]; and finally (5) The potential emergence of IVM-resistant O. volvulus, may limit the long-term effectiveness of MDA and, in time, undermine all of the gains achieved by onchocerciasis control programs [21–29]. Originally developed for veterinary use, IVM was re-purposed for use as a microfilaricidal drug in humans, initially to great effect [30,31]. While current evidence for IVM resistance in O. volvulus is far from definitive, it is quite clear that sub-optimal responses to IVM in the treatment of river blindness have been identified, in particular, as manifested by faster rates of microfilarial skin repopulation linked to decreased effects of IVM on female worm fecundity [32]. It should be noted that IVM was first used for many years to prevent heartworm disease caused by the filarial parasite Dirofilaria immitis in domestic dogs and cats, but it has been demonstrated that IVM-resistant D. immitis is already circulating in the United States [33]. Complicating the challenges with relying only on MDA with IVM is that IVM is not administered to children under 5 years old and a macrofilaricidal drug, doxycycline, cannot be given to children under 9 thus limiting the indications for these two drugs. In addition, doxycycline requires 6 weeks of treatment to be effective which further diminishes its utility [34]. Thus, children are not only vulnerable to infection but become reservoirs for transmission [35].