Immune responses to porcine epidemic diarrhea virus (PEDV) in swine and protection against subsequent infection.

Understanding the immune responses against Porcine epidemic diarrhea virus (PEDV) is important to prevent infection and to design control strategies. We evaluated both systemic and mucosal immune responses to PEDV in pigs and assessed if prior exposure to virus protects against re-infection. Three-week-old pigs were infected with PEDV and immune response in blood, intestine, and mesenteric lymph node (MLN) was evaluated. At 30 dpi, virus exposed pigs were challenged with a field isolate of PEDV and immune response at 5 d post challenge was evaluated. We found that PEDV RNA persists in the intestine even after fecal shedding of the virus was stopped at 28 dpi and pigs previously exposed to PEDV are protected from virus shedding after re-infection. PEDV infection induced both humoral and cell mediated immune response with an increase in PEDV specific IgA and IgG antibodies in intestine and serum. Flow cytometry analysis showed a significantly higher frequency of B cells and lower frequency of T cells at 4 dpi. The frequency of CD4/CD8 double positive (DP) memory T cells was significantly increased in the MLN of challenged animals. These studies may provide further insights into understanding the mucosal immune response to PEDV and its role in protection against disease.

Prior infection with intestinal coronaviruses moderates symptom severity and mortality in patients with COVID-19: A hypothesis and preliminary evidence.

The pandemic of acute respiratory illness caused by the novel betacoronavirus SARS-CoV-2, officially designated COVID-19, has attained the proportions of a global health crisis. Though all nations of the world have been affected by this disease, there have been marked cross-national variations in prevalence, severity and mortality rates. Various explanations, based on demographic, social and climatic factors, have been suggested to account for this variability, but these remain unverified to date. Based on recent research findings suggesting that human enterocytes may serve as a point of entry for SARS-CoV-2, leading to intestinal viral replication, this paper puts forward the hypothesis that prior intestinal infection with coronaviruses, either symptomatic or asymptomatic, may moderate this process and minimize the severity of SARS-CoV-2 infection. This hypothesis is supported by evidence on the gastrointestinal manifestations of SARS-CoV-2 and related infections, on the geographical patterns observed in the variability of COVID-19 mortality, and on the occurrence and geographical distribution of outbreaks of diarrheal disease, as well as asymptomatic infection, with human coronaviruses as verified by direct or serological testing. Preliminary supporting evidence based on national and international health statistics is presented, along with suggestions on more robust methods by which this hypothesis may be tested. If the proposal put forth in this paper can be confirmed either wholly or in part, it would have significant implications in terms of strategies aimed at minimizing the severity of COVID-19 in a clinical setting.

Clinical Insights into the Gastrointestinal Manifestations of COVID-19.

The month of December 2019 became a critical part of the time of humanity when the first case of coronavirus disease 2019 (COVID-19) was reported in the Wuhan, Hubei Province in China. As of April 13th, 2020, there have been approximately 1.9 million cases and 199,000 deaths across the world, which were associated with COVID-19. The COVID-19 is the seventh coronavirus to be identified to infect humans. In the past, Severe Acute Respiratory Syndrome and Middle East Respiratory Syndrome were the two coronaviruses that infected humans with a high fatality, particularly among the elderly. Fatalities due to COVID-19 are higher in patients older than 50 years of age or those with multimorbid conditions. The COVID-19 is mainly transmitted through respiratory droplets, with the most common symptoms being high fever, cough, myalgia, atypical symptoms included sputum production, headache, hemoptysis and diarrhea. However, the incubation period can range from 2 to 14 days without any symptoms. It is particularly true with gastrointestinal (GI) symptoms in which patients can still shed the virus even after pulmonary symptoms have resolved. Given the high percentage of COVID-19 patients that present with GI symptoms (e.g., nausea and diarrhea), screening patients for GI symptoms remain essential. Recently, cases of fecal-oral transmission of COVID-19 have been confirmed in the USA and China, indicating that the virus can replicate in both the respiratory and digestive tract. Moreover, the epidemiology, clinical characteristics, diagnostic procedures, treatments and prevention of the gastrointestinal manifestations of COVID-19 remain to be elucidated.

Evaluation of the immune response in conventionally weaned pigs infected with porcine deltacoronavirus.

Although porcine deltacoronavirus (PDCoV) is a significant pandemic threat in the swine population and has caused significant economic losses, information regarding the immune response in conventionally weaned pigs infected with PDCoV is scarce. Hence, the immune response in conventionally weaned pigs infected with PDCoV was assessed after challenge and rechallenge. After the first challenge, obvious diarrhea and viral shedding developed successively in all pigs in the four inoculation dose groups from 3 to 14 days postinfection (dpi), and all pigs recovered (no clinical symptoms or viral shedding) by 21 dpi. All pigs in the four groups exhibited significantly increased PDCoV-specific IgG, IgA and virus-neutralizing (VN) antibody (Ab) titers and IFN-γ levels in the serum after the first challenge. All pigs were completely protected against rechallenge at 21 dpi. The serum levels of PDCoV-specific IgG, IgA, and VN Abs increased further after rechallenge. Notably, the IFN-γ level declined continuously after 7 dpi. In addition, the levels of PDCoV-specific IgG, IgA and VN Abs in saliva increased significantly after rechallenge and correlated well with the serum Ab titers. Furthermore, the appearance of clinical symptoms of PDCoV infection in conventionally weaned pigs was delayed with reduced inoculation doses. In summary, the data presented here offer important reference information for future PDCoV animal infection and vaccine-induced immunoprotection experiments.

Assessment of hemagglutination activity of porcine deltacoronavirus.

Porcine deltacoronavirus (PDCoV) is an emerging swine enteric coronavirus that causes diarrhea in piglets. However, the biological characteristics of PDCoV are unclear. In this study, the hemagglutination (HA) abilities of two PDCoV strains (CH-01 and HNZK-04) were investigated. Our results showed that PDCoV has the ability to agglutinate rabbit erythrocytes after virion pretreatment with trypsin or neuraminidase. Additionally, the HA assay results showed a significant positive correlation with the infectious viral titer. Our results suggest that assessing the HA activity of PDCoV may be a useful diagnostic method for investigating and surveilling PDCoV infections.