Research Article: ICR suckling mouse model of Zika virus infection for disease modeling and drug validation

Date Published: October 24, 2018

Publisher: Public Library of Science

Author(s): Yu-Hsuan Wu, Chin-Kai Tseng, Chun-Kuang Lin, Chih-Ku Wei, Jin-Ching Lee, Kung-Chia Young, Marcus VG Lacerda.

Abstract: BackgroundZika virus (ZIKV) infection causes diseases ranging from acute self-limiting febrile illness to life-threatening Guillain–Barré Syndrome and other neurological disorders in adults. Cumulative evidence suggests an association between ZIKV infection and microcephaly in newborn infants. Given the host-range restrictions of the virus, a susceptible animal model infected by ZIKV must be developed for evaluation of vaccines and antivirals. In this study, we propose a convenient mouse model for analysis of neurological disorders caused by ZIKV.MethodologySix-day-old immunocompetent ICR suckling mice were used in the experiment. Different inoculum virus concentrations, challenge routes, and challenge times were assessed. Viremic dissemination was determined in the liver, spleen, kidney, and brain through Western blot assay, plaque assay, absolute quantification real-time PCR, and histological observation. Azithromycin, a well-characterized anti-ZIKV compound, was used to evaluate the ICR suckling mouse model for antiviral testing.ConclusionsSigns of illness and neurological disease and high mortality rate were observed in mice injected with ZIKV intracerebrally (102 to 105) and intraperitoneally (103 to 105). Viremic dissemination was observed in the liver, spleen, kidney, and brain. ZIKV transmitted, rapid replicated, and induced monocyte infiltration into the brain approximately 5 to 6 days post inoculum. Azithromycin conferred protection against ZIKV-caused neurological and life-threatening diseases. The developed model of ZIKV infection and disease can be used for screening drugs against ZIKV and discovering the underlying mechanism of ZIKV pathogenesis.

Partial Text: Mosquito-borne Zika virus (ZIKV), which belongs to the Flavivirus genus of the Flaviviridae family, is an emerging threat to human health worldwide [1]. The genome of ZIKV consists of a single-stranded positive sense RNA, which encodes a single polypeptide [2, 3]. The single polypeptide is processed by viral and host proteases to form mature viral proteins, including three structural proteins [core (C), pre-membrane (prM), and envelope (E)] and seven non-structural proteins (NS1, NS2A, NS2B, NS3, NS4A, NS4B, and NS5) [4]. ZIKV (strain MR766) was first isolated from sentinel rhesus monkeys in the Zika forest of Uganda in 1947 [5]. ZIKV was also isolated from Aedes africanus mosquito in the Zika forest. Few ZIKV infection cases were reported around African and Asian countries during 1960s–1980s, and ZIKV was neglected for years until 2007 [6]. In 2007, ZIKV infection attracted global attention due to the outbreak in the Yap Island of Micronesia, which was the first spread of ZIKV infection outside Africa and Asia [7, 8]. In 2013–2014, another ZIKV outbreak was reported in French Polynesia, and more than 28,800 people were infected by the virus [9]. Thereafter, ZIKV has spread rapidly throughout the Pacific region. Most importantly, in UK, a man who visited French Polynesia at 2014 was diagnosed with ZIKV; in this case, ZIKV RNA was detected in the semen 2 months post onset of the syndromes, which underlined the potential of sexual transmission of the virus [10]. In 2015, the first ZIKV breakout in America was reported in Brazil; the Brazilian Ministry of Health reported a 20-fold increase in cases of neonatal microcephaly, which was geographically and temporally correlated with the ZIKV outbreak [11, 12]. Most patients infected by ZIKV present mild symptoms, including moderate fever, headache, myalgia, conjunctivitis, and rash, which are similar to those of infection by other Flavivirus, such as dengue virus or West Nile virus [13–17]. Recent evidence demonstrated that ZIKV infection leads to severe syndromes, such as Guillain–Barré syndrome (GBS) and microcephaly in adults and infants, respectively [14–16]. GBS is an autoimmune disorder in which the immune system attacks the nervous system [18]. The key phenomenon of GBS is the infiltration of activated lymphocytes and monocytes in nerve tissues, leading to acute or subacute flaccid paralysis [13, 19]. At present, ZIKV spreads rapidly in Africa, America, and Asia Pacific [5]. No approved antivirals or vaccines are available for treatment of ZIKV infection. Therefore, a suitable animal model must be developed for investigating therapeutics or vaccines against ZIKV infection and related diseases.

In the present study, we established a ZIKV-infected ICR suckling mice model for investigating the propagation of ZIKV infection and, especially, the antiviral drug development in vivo. The ICR suckling mice model is susceptible for ZIKV infection by using both i.p. and i.c. injection methods and provide infection with high viral loads in the brain, which is consistent with severe neurological symptom in human [12, 14, 25]. Our results further clearly illustrated the level of ZIKV propagation in different tissues, including liver, spleen, and kidney, which indicated that ZIKV distributed systemically in the ICR suckling mice and provided the evidence of ZIKV distribution in the infected individuals. Recently, Retallack et al. reported that Az could prevent ZIKV infection in vitro [23]. Consistently, our study further confirmed that Az could protect mice from lethal ZIKV infection in vivo. To date, ZIKV has been already spread out of the world for years, therefore, a therapeutic treatment against ZIKV infection is urgently needed. Retallack et al. and our results provide a potential therapeutics for treatment of ZIKV infection.