Liu et al. Parasites Vectors (2020) 13:616 https://doi.org/10.1186/s13071-020-04494-4 Parasites & Vectors REVIEW Open Access Human gnathostomiasis: a neglected food-borne zoonosis Guo‑Hua Liu1,2, Miao‑Miao Sun2, Hany M. Elsheikha3, Yi‑Tian Fu1, Hiromu Sugiyama4, Katsuhiko Ando5, Woon‑Mok Sohn6, Xing‑Quan Zhu7* and Chaoqun Yao8* Abstract Background: Human gnathostomiasis is a food‑borne zoonosis. Its etiological agents are the third‑stage larvae of Gnathostoma spp. Human gnathostomiasis is often reported in developing countries, but it is also an emerging dis‑ ease in developed countries in non‑endemic areas. The recent surge in cases of human gnathostomiasis is mainly due to the increasing consumption of raw freshwater fsh, amphibians, and reptiles. Methods: This article reviews the literature on Gnathostoma spp. and the disease that these parasites cause in humans. We review the literature on the life cycle and pathogenesis of these parasites, the clinical features, epidemi‑ ology, diagnosis, treatment, control, and new molecular fndings on human gnathostomiasis, and social‑ecological factors related to the transmission of this disease. Conclusions: The information presented provides an impetus for studying the parasite biology and host immunity. It is urgently needed to develop a quick and sensitive diagnosis and to develop an efective regimen for the manage‑ ment and control of human gnathostomiasis. Keywords: Gnathostoma spp., Gnathostomiasis, Food‑borne zoonosis Background Te frst human case of gnathostomiasis was reported Human gnathostomiasis, a food-borne zoonosis, is from Tailand in 1889, and was attributed to infection caused by the third-stage larvae (L3) of Gnathostoma spp. by Cheiracanthus siamensis (Levinseen 1889). Shortly [1]. Humans are infected by these nematodes by consum- afterwards, Leiper (1891) found that C. siamensis was ing raw or undercooked fsh, frogs, snakes or poultry that morphologically identical to Gnathostoma spinigerum, contain the L 3 [2]. Te most common clinical signs and and thus considered the former a synonym of the latter. symptoms of the disease are migratory cutaneous swell- However, the life cycle of G. spinigerum was not eluci- ings and eosinophilia. In severe cases, L3 also invade dated until 1936 [4]. To date, approximately 5000 cases of internal organs and tissues such as the liver, eyes, nerves, human gnathostomiasis have been reported worldwide, spinal cord and brain, which can result in blindness, mainly from endemic areas in Japan and China, Tailand nerve pain, paralysis, coma and even death [3]. and other parts of Southeast Asia, Mexico, and Colombia and Peru in South America [1, 3]. Gnathostomiasis has also been reported, albeit infrequently, in travelers from developed countries who have visited endemic areas [3, *Correspondence: [email protected]; [email protected] 5–8]. Furthermore, autochthonous gnathostomiasis has 7 College of Veterinary Medicine, Shanxi Agricultural University, Taigu, Shanxi 030801, People’s Republic of China been reported in several non-endemic countries [9–12]. 8 Department of Biomedical Sciences and One Health Center Terefore, human gnathostomiasis is considered an for Zoonoses and Tropical Veterinary Medicine, Ross University School emerging global zoonosis [3, 13]. of Veterinary Medicine, P.O. Box 334, Basseterre, St Kitts and Nevis Full list of author information is available at the end of the article © The Author(s) 2020. 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The Creative Commons Public Domain Dedication waiver (http://creat iveco mmons .org/publi cdoma in/ zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data. Liu et al. Parasites Vectors (2020) 13:616 Page 2 of 11 Te increase in reports of human gnathostomiasis may they develop into L 3. If L3 in the second intermediate be due to changes in eating habits as a result of improved host, transport or paratenic host are ingested by a defni- living standards, and also in improvements in health tive host (e.g., dogs, cats, pigs or weasel), they migrate to care systems for disease reporting [14]. Te eradication the liver and the abdominal cavity after penetrating the of gnathostomiasis is challenging because of the world- gastric wall. Four weeks later they return to the gastric wide distribution of Gnathostoma spp. and increasing wall [1] and develop into adults. Tis development from demand for exotic dishes such as marinated or raw fsh L3 to adult usually takes 6-8 months. Te defnitive host [1, 14, 15]. Terefore, an efective prevention and con- starts to excrete the parasite eggs into the environment trol strategy should ideally be implemented for this dis- in its feces approximately 8 to 12 months after ingestion ease. Here, we comprehensively review several aspects of of L3 [25, 26]. When L 3 are eaten by paratenic hosts such human gnathostomiasis and discuss future prospects for as frogs, snakes, birds and mammals including humans, the improvement of public perception of the importance they migrate through their tissues and remain encysted of this parasitic disease. in their muscles. Human gnathostomiasis can occur through three Gnathostoma spp. and their life cycles modes of transmission: oral, transplacental and skin A gnathostome nematode was frst discovered in 1836 in wounds. However, this parasitic disease is mainly caused the stomach of a young tiger that had died of aortic rup- by the ingestion of raw or undercooked meat of interme- ture at London Zoo [16]. Since then, Gnathostoma spp. diate hosts, such as fsh, frogs, snakes or poultry, which (Nematoda: Gnathostomatidae) have been determined to contains L3 [27]. Oral infection can also occur through be the etiological agents of human gnathostomiasis [17]. drinking water contaminated with infected copepods Among the 12 species in the genus, at least fve, G. binu- [28]. Transplacental infection only occurs in pregnant cleatum, G. doloresi, G. hispidum, G. nipponicum and G. women with a heavy infection of gnathostome larvae, spinigerum, cause human disease [18, 19]. Te species which is rare [29]. L3 harbored in the infected meat of most frequently found in humans and most widely dis- intermediate hosts can penetrate the skin of humans, tributed around the world is G. spinigerum; G. binuclea- particularly through wounds [30]. tum is found in the Americas [1]. Sporadic cases caused by G. doloresi, G. hispidum, and G. nipponicum have Pathogenesis and clinical presentation been documented in Asia [20–23]. Humans are not defnitive hosts of Gnathostoma spp., Gnathostome eggs are oval in shape and have a mucoid and L3 cannot mature into adults in them [31]. L3 can, plug at one or both ends, depending on the species however, cause damage to their tissues and/or organs by [24]. Te early L3 (EL3) and the advanced L3 (AdL3) of inducing host reactions, like infammation and allergy, G. spinigerum in the second intermediate host usually when they migrate and secrete excreta and toxins [32]. L3 measure 0.85–1.38 in length × 0.10–0.15 mm in diam- may cause damage to vital organs and the central nervous eter and 2.30–4.40 in length × 0.25–0.43 mm in diam- system (CNS), resulting in detrimental outcomes includ- eter, respectively. AdL3 have a characteristic head bulb ing the sudden death of an infected individual [33, 34]. of 93 × 221 μm on average, which often bears four rows, Te larvae release excretory-secretory products (ES) with and occasionally fve rows, of hooklets, a long muscular divergent functions that contribute to diferent parasite esophagus 0.63–1.22 mm in length and two pairs of cer- behaviors including cutaneous and visceral larva migrans vical sacs 0.33–0.75 mm in length. [35, 36]. Recent studies have demonstrated that G. spini- Gnathostoma nematodes require two intermediate gerum ES antigens modulate monocyte function via hosts and one defnitive host to complete their life cycles inhibition of Fc gamma receptor I expression, and trig- (Fig. 1). In general, the adult worms live and spawn in a ger apoptosis of the peripheral blood mononuclear cells tumor-like mass in the stomach of the defnitive host (e.g., mainly via the extrinsic pathway [37, 38]. cat, tiger, leopard or dog in the case of G. spinigerum). Gnathostoma larvae can migrate to the skin though Te eggs are released in the host’s feces into the environ- subcutaneous tissue, and penetrate other tissues and ment, where they develop and hatch into the frst-stage organs including the eyes, ears, breasts, lungs, gastro- larvae (L1) in freshwater within 7 days at 28 °C. L1 are intestinal tract, thoracic spinal cord, genitourinary sys- then ingested by the frst intermediate host, freshwater tem and CNS [8, 39]. Clinical features mostly manifest copepods (usually of the genera Cyclops, Eucyclops and as cutaneous and visceral migrans, depending on which Mesocyclops), where they develop into the second-stage parts of the body have been invaded. Within 1 or 2 days larvae (L2). When the infected copepods are consumed of ingestion, a Gnathostoma larva migrates through the by the second intermediate host such as a fsh or tadpole, gastrointestinal tract wall and the liver.