Excessive antimicrobial usage and deficiencies in hygiene in meat production systems may result in undesirable human health hazards, such as the presence of antimicrobial drug residues and non-typhoidal Salmonella (NTS), including antimicrobial resistant (AMR) NTS. Recently, Vietnam has witnessed the emergence of integrated intensive animal production systems, coexisting with more traditional, locally-sourced wet markets. To date no systematic studies have been carried out to compare health hazards in beef, pork and chicken in different production systems. We aimed to: (1) estimate the prevalence of antimicrobial residues in beef, pork and chicken meat; (2) investigate the prevalence and levels of NTS contamination; and (3) investigate serovar distribution and AMR against critically important antimicrobials by animal species and type of retail (wet market vs. supermarket) in Vietnam. Fresh pork, beef and chicken meat samples (N=357) sourced from wet markets and supermarkets in Ho Chi Minh City (HCMC), Hanoi and Dong Thap were screened for antimicrobial residues by PremiTest, and were further investigated by Charm II. Samples from HCMC (N=113) were cultured using ISO 6579:2002/Amd 1:2007. NTS bacteria were quantified using a minimum probable number (MPN) technique. NTS isolates were assigned to serovar by Multilocus Sequence Typing (MLST), and were investigated for their phenotypic susceptibility against 32 antimicrobials. A total of 26 (7.3%) samples tested positive by PremiTest (9.5% beef, 4.1% pork and 8.4% chicken meat). Sulfonamides, tetracyclines and macrolides were detected by Charm in 3.1%, 2.8% and 2.0% samples, respectively. Overall, meat samples from wet markets had a higher prevalence of residues than those from supermarkets (9.6% vs. 2.6%) (p=0.016). NTS were isolated from 68.4% samples from HCMC. Chicken samples from wet markets had by far the highest NTS counts (median 3.2 logMPN/g). NTS isolates displayed high levels of resistance against quinolones (52.2%) and β-lactams (49.6%), but low levels against 3rd generation cephalosporins (4.4%) and aminoglycosides (0.8%). The highest adjusted prevalence of multidrug resistance (MDR) corresponded to isolates from chicken meat and pork (OR 8.3 and 1.8, respectively) (baseline=beef). S. Kentucky was the most common serovar identified (11 from chicken, 1 from beef) and 91.7% isolates was MDR. 11/12 isolates corresponded to ST198, a worldwide-disseminated multi-resistant NTS clone. We recommend stepping up policy measures to promote responsible antimicrobial use in animal production, as well as awareness about withdrawal periods to limit the hazard of residues in animal products, and improving slaughtering/hygiene procedures to limit cross-contamination with NTS, particularly in poultry wet markets.

Chicken is, among farmed species, the target of the highest levels of antimicrobial use (AMU). There are considerable knowledge gaps on how and when antimicrobials are used in commercial small-scale chicken farms. These shortcomings arise from cross-sectional study designs and poor record keeping practiced by many such farmers. Furthermore, there is a large diversity of AMU metrics, and it is not clear how these metrics relate to each other. We performed a longitudinal study on a cohort of small-scale chicken farms (n = 102) in the Mekong Delta (Vietnam), an area regarded as a hotspot of AMU, from October 2016 to May 2018. We collected data on all medicine products administered to 203 flocks with the following aims: (1) to describe types and quantities of antimicrobial active ingredients (AAIs) used; (2) to describe critical time points of AMU; and (3) to compare AMU using three quantitative metrics: (a) weight of AAIs related to bird weight at the time of treatment (mg/kg at treatment); (b) weight of AAIs related to weight of birds sold (mg/kg sold); and (c) “treatment incidence” (TI), or the number of daily doses per kilogram of live chicken [Vietnamese animal daily dose (ADDvetVN)] per 1,000 days. Antimicrobials contained in commercial feed, administered by injection (n = N = 6), or antimicrobials for human medicine (n = N = 16) were excluded. A total of 236 products were identified, containing 42 different AAIs. A total of 76.2% products contained AAIs of “critical importance” according to the World Health Organization (WHO). On average, chickens consumed 791.8 (SEM ±16.7) mg/kg at treatment, 323.4 (SEM ±11.3) mg/kg sold, and the TI was 382.6 (SEM ±5.5) per 1,000 days. AMU was more common early in the production cycle and was highly skewed, with the upper 25% quantile of flocks accounting for 60.7% of total AMU. The observed discrepancies between weight- and dose-based metrics were explained by differences in the strength of AAIs, mortality levels, and the timing of administration. Results suggest that in small-scale chicken production, AMU reduction efforts should preferentially target the early (brooding) period, which is when birds are most likely to be exposed to antimicrobials, whilst restricting access to antimicrobials of critical importance for human medicine.

Raising chickens in small-scale flocks following all-in-all-out management is common in the Mekong Delta of Vietnam. These flocks represent an intermediate category between backyard and intensive (industrial) farming systems. However, little is known about the occurrence and burden of disease and/or mortality in such flocks, and their potential association with antimicrobial usage (AMU). We investigated mortality, disease and weekly antimicrobial use (AMU) in 124 cycles of meat chicken flocks raised in 88 farms in the Mekong Delta of Vietnam (with a median cycle duration of 18 weeks [inter-quartile range IQR 17-20]). We visited each farm 4 times per cycle to review data collected weekly by the farmers on clinical signs, mortality, and AMU. The overall probability of disease and AMU were 0.31 (95% CI 0.29-0.32) and 0.26 (95% CI 0.24-0.28), respectively. The average weekly incidence of mortality was 2.6 (95% CI 2.2-3.0) per 100 birds. Both the probabilities of a flock experiencing disease and mortality, as well as of using antimicrobials decreased with the flock's age. However, mortality peaked at the 5-10 week period. The only significant explanatory factors associated with presence of disease was the stage of production ≥5 weeks (protective) (OR ≤ 0.51). Factors independently associated with AMU (p < 0.05) were: (1) Number of chickens (log) (OR=1.46), (2) Stage of production ≥5 weeks (OR≤0.67) (protective), (3) Cao Lanh district (OR=2.23), (4) Density of veterinary drug shops at commune level (log) (OR=1.58), and (5) Disease in flocks (OR=1.80). Factors independently associated with overall increased weekly incidence of mortality (p < 0.05) were: (1) High level of education attainment (secondary education or higher) (Hazard rate Ratio [HR]=1.70), (2) number of chickens (log) (HR=1.39), and (3) Stage of production >5 weeks (HR≤2.14). In flocks reporting disease, AMU significantly reduced the incidence of mortality (HR=0.90). These results confirm an exceptionally high mortality in chicken flocks in the area, jeopardizing the profitability and sustainability of these small-scale farming systems. The data also suggest an association between nearby access to antimicrobials and AMU, and a high correlation of AMU over consecutive cycles. The atomized farming landscape of the Mekong Delta, the high incidence of disease and mortality, and the unrestricted and easy access to antimicrobials present major challenges to the implementation of policies aimed at AMU reductions.

We investigated antimicrobial residues, non-typhoidal Salmonella (NTS), Vibrio spp. and their associated antimicrobial resistance (AMR), in shrimps locally purchased in Ho Chi Minh City (Vietnam). In addition, we investigated the relationship between AMR in NTS, Vibrio spp. and antimicrobial residue in the same sample. A total of 40 samples of shrimp heads/shells from different retail sources was cultured using ISO 6579–1:2017 (NTS) and ISO/TS 21872–1:2007 (Vibrio spp.). Phenotypic antimicrobial susceptibility was investigated using Vitek (NTS, 34 antimicrobials) and disk diffusion (Vibrio spp., 12 antimicrobials). A total of 9 (22.5%) samples contained antimicrobial residue, including tetracyclines, fluoroquinolones, sulfonamides and macrolides (in 7.5%, 7.5%, 2.5% and 2.5% of samples, respectively). Shrimp samples from supermarkets had a higher prevalence of antimicrobial residue than those purchased in street markets (50% vs. 13.3%) (p = 0.049). A total of 30 (75%) samples were contaminated with NTS. All samples contained Vibrio spp., with V. parahaemolyticus being most common (87.5% samples). A total of 58.9% NTS isolates were multidrug resistant. With regards to the highest priority, critically important antimicrobials, the highest resistance corresponded to quinolones (14.4–47.8%), followed by 3rd and 4th generation cephalosporins (3.3–7.8%). Vibrio spp. isolates were characterised by their high resistance against ampicillin (82.7%) and 3rd generation cephalosporins (8.3–16.5%). Extended Spectrum Beta-Lactamase (ESBL) activity was detected in 28.1% V. parahaemolyticus isolates. Half of ESBL-positive V. parahaemolyticus strains harboured blaCTX-M1. We found an association between the presence of residues and the number of resistances for NTS (p = 0.075) and Vibrio spp. isolates (p = 0.093) from the same sample. These findings suggest that the presence of residues may contribute to the selection of AMR in foodborne pathogens in shrimps. Authorities should strengthen policies aiming at restricting inappropriate antimicrobial usage in shrimp farming, and step up monitoring of antimicrobial residues and food-borne pathogens at retail in Vietnam.

Commercial small-scale chicken farms managed as all-in-all-out but operating with low standards of hygiene/biosecurity are increasingly common in Vietnam. These conditions facilitate the transmission of gastrointestinal helminths. However, there are no published data on helminths in these systems. We aimed (1) to determine the prevalence/burden of gastrointestinal helminths in small-scale commercial flocks in the Mekong Delta region and (2) to investigate the association between worm burdens and birds’ weight and disease status. Randomly selected chickens (n = 120) from ‘normal’ flocks were investigated at the end of their production cycle (~ 18 weeks), as well as 90 chickens from ‘diseased’ flocks with signs of respiratory and/or severe disease. The gastrointestinal tract of chickens was dissected and all visible helminths were identified and counted. A total of 54.2% and 54.4% normal and diseased chickens contained helminths. Among colonised birds, the diseased ones harboured a higher mass of helminth worms than normal (healthy) birds (3.8 ± SD 8.6 g vs. 1.9 ± SD 6.3 g, respectively). Eight species were identified, including nematodes (Ascaridia galli, Cheilospirura hamulosa and Heterakis gallinarum), cestodes (Hymenolepis, Raillietina cesticillus, Raillietina echinobothrida, Raillietina tetragona,) and one trematode (Echinostomatidae). Heterakis gallinarum was the most prevalent helminth (43.3% and 42.2% in normal and sick chickens, respectively), followed by A. galli (26.7% and 41.1%). Colonised chickens weighed 101.5 g less than non-colonised birds. Colonisation was higher during the rainy months (May–November) for both H. gallinarum and A. galli. Anthelminthic usage was not associated with reduced helminth burdens. We recommend upgrading cleaning and disinfection and limiting access to ranging areas to control helminths in small-scale chicken flocks.

In the Mekong Delta region of Vietnam, small-scale chicken farming is common. However, high levels of disease or mortality in such flocks impair economic development and challenge the livelihoods of many rural households. We investigated 61 diseased small-scale flocks (122 chickens) for evidence of infection with 5 bacteria, 4 viruses, and helminths. Serological profiles (ELISA) were also determined against 6 of these pathogens. The aims of this study were the following: (1) to investigate the prevalence of different pathogens and to compare the probability of detection of bacterial pathogens using PCR and culture; (2) to investigate the relationship between detection of organisms in birds' tissues and the observed morbidity and mortality, as well as their antibody profile; and (3) to characterize risk factors for infection with specific viral or bacterial pathogens. We used PCR to test for viral (viruses causing infectious bronchitis [IB], highly pathogenic avian influenza [HPAI], Newcastle disease, and infectious bursal disease [IBD]) and bacterial pathogens (Mycoplasma gallisepticum, Pasteurella multocida, Avibacterium paragallinarum, and Ornithobacterium rhinotracheale [ORT]). The latter two were also investigated in respiratory tissues by conventional culture. Colisepticemic Escherichia coli was investigated by liver or spleen culture. In 49 of 61 (80.3%) flocks, at least one bacterial or viral pathogen was detected, and in 29 (47.5%) flocks, more than one pathogen was detected. A. paragallinarum was detected in 62.3% flocks, followed by M. gallisepticum (26.2%), viruses causing IBD (24.6%) and IB (21.3%), septicemic E. coli (14.8%), ORT (13.1%), and HPAI viruses (4.9%). Of all flocks, 67.2% flocks were colonized by helminths. Mortality was highest among flocks infected with HPAI (100%, interquartile range [IQR]: 81.6-100%) and lowest with flocks infected with ORT (5.3%, IQR: 1.1-9.0%). The results indicated slight agreement (kappa ≤ 0.167) between detection by PCR and culture for both A. paragallinarum and ORT, as well as between the presence of cestodes and ORT infection (kappa = 0.317). Control of A. paragallinarum, viruses causing HPAI, IBD, and IB, M. gallisepticum, and gastrointestinal helminths should be a priority in small-scale flocks.