In free-roaming dog populations, does egg-based oral rabies vaccination programmes result in improved bait efficacy?

Free-roaming dogs in locations chosen at random within two urban regions: Panjim and Goa Velha, India.

404 dogs.

• Two bait constructs included a placebo vaccine sachet incorporated in an egg-flavoured bait matrix or coated with a commercially available pet food gravy.
• The egg-baits were locally manufactured in India using ingredients and method as the proprietor bait from IDT Biologika, Dessau-Rosslau in Germany.
• Egg baits were then frozen in a foil zip-bag before use.
• Outer layer of the sachet used in the study is liquid absorbent and hence 15 sachets where placed in a zip-bag and before distribution, poured in and mixed with 100 g of commercially available chicken-flavoured pet food gravy, which coated the sachet.
• The capsule was made with biodegradable foil covered with a fleece that can absorb fluids.
• A colourant and sucrose dissolved in water was also added for detectability if contents of sachet had been perforated into the oral cavity for both baits.
• The field study took place on the 11 and 12 July 2018.
• Teams were trained for half a day on the bait handout method before being deployed.
• Three teams consisting of two people on moped distributed baits in randomly allocated sections of the study area between 7:00 and 17:00.
• Baits were defrosted shortly before each vaccination session.
• Type of bait offered to each dog was randomly pre-determined.
• Staff were trained to approach dogs indirectly, avoid eye contact, drop the bait in front of the animal from a distance and continue walking, then from a distance, record their observations.

Non-blinded randomised control trial.

• Bait interaction including type of bait, acceptance, consumption, sachet perforation, bait handling time, bait outcome and bait efficacy.
  
  
  • Bait acceptance was defined as either sniffed, licked, ignored or did not acknowledge the bait.
  • Consumption was recorded as whether the dog took the bait into the mouth, and what percentage of the bait was consumed (< 50%, > 50%, 100%).
  • Time observed included duration of bait manipulation by the dogs (< 10, 10–30, 30–60 or > 60 seconds).
  • Outcome of whether the sachet remnants were swallowed or discarded was also recorded.
  • Bait efficacy was recorded as the staff’s assessment. The sachet contained active oral rabies vaccine (ORV), by observing the release of the dyed-water in the oral cavity.
• An unknown field was also included if the outcome was not observed (if the dog took the bait out of sight for example).
• Data was recorded whether the dog was alone, or with other dogs, and if so, with how many, as well as age, sex and size.
  
  
  • Age was estimated by the staff (adult / juvenile / puppy).

• Higher proportion of dogs consumed the egg bait than those offered gravy baits.
  
  
  • 162/209 (77.5%) with egg baits.
  • 134/195 (68.7%) with gravy baits.
  • P value was 0.047, Chi² value was 3.94, meaning results were significant.
• Where bait perforation status was observed, egg baits were perforated more often than gravy baits meaning greater chance of vaccine uptake.
  
  
  • 133/162 (91.1%) with egg baits.
  • 89/123 (72.4%) with gravy baits.
  • P value was < 0.001, Chi² value was 14.98, meaning results were significant.

• Considerable variation between teams / staff which may show as an inconsistency in bait distribution methods.
  
  
  • The consumption of the bait is highly influenced by the way the team approaches the dog and how they dropped / tossed the bait.
• Staff only had half a day of training and were not followed-up with supervision and evaluation to ensure competency and consistency in distribution of the bait.
• Monitoring methods was subjective and up to staff discretion, which may skew the results depending on the observer.

• Free-roaming dogs in four municipalities, consisting of two municipalities in Rayong province (Choeng Noen, Phe), one in Phetchaburi province (Cha Um), and another in Nakhonsri Thammarat province (Thung Song).
• Another rural area in the eastern part of Thailand, Tapraya, was included on a later date.

1,930 dogs.

• SPBN GASGAS vaccine (Ceva Innovation Centre GmbH, Dessau,Germany) was used in these oral rabies vaccination (ORV).
  
  
  • Stored at –20^oC and transported using dry ice.
  • Kept frozen in standard cool boxes at –18^oC overnight before field use.
• Sachets were filled with the liquid vaccine virus.
• Two different bait types were used:
  
  
  • manufactured egg-flavoured bait;
  • locally produced intestine bait.
    
    
    • The study team observed further optimisation of the egg bait by putting tuna or chicken-flavoured cat liquid snacks available from local markets on the outer surface immediately before presenting the bait to the dog. These baits were marked as egg+ baits.
• Intestine baits were prepared by inserting the sachet with the frozen vaccine into a segment of pork intestine.


• Placed immediately back in the freezer to prevent vaccine thawing.
• Sites for sampling was identified with the local municipality workers and dog caretakers to estimate free-roaming dogs could be found from each site.
• Vaccination team members received brief training on ORV, including vaccine bait handling, techniques for approaching dogs, methods for offering the vaccine bait, recording vaccine bait handling by individual dogs, interpreting effectiveness of vaccination attempt (defined as ‘perforated sachet or when dog chewed at least five times before swallowing bait and sachet’), and on retrieving the discarded vaccine sachet after bait consumption.
• Bait not accepted was recollected to prevent human contact with the baits.
• Oral vaccination campaigns were done in a week for each municipality.
• One bait type was allocated to a team in the study, and the team would decide whether to use the liquid snack on the egg bait depending on whether the dogs seemed to be difficult to access.

Non-blinded control trial.

• Group sizes of the dogs offered the ORV.
• How the bait was offered (directly to the dog, dropped in front of the dog when passing by, tossed / thrown to the dog).
• Dog demographic data (sex, age, size, single or together with other dogs).
• Type of staff offering the bait:
  
  
  • municipality or Department of Livestock Development staff;
  • dog caretakers;
  • animal / public health volunteers.
• Percentage of dogs interested in the bait offered that chewed very shortly (< 10 seconds), swallowed the sachet, and considered vaccinated (defined as ‘perforated sachet or when dog chewed at least 5 times before swallowing bait and sachet’) per bait type.
• Location / site of the dogs.
• Vaccination coverage in study areas.

• Most dogs were interested (meaning uptake of the vaccine bait) in the intestine bait, followed by the egg+ bait, with the egg bait garnering the least interest:
  
  
  • 1209/1302 (92.9%) for intestine bait;
  • 256/276 (92.8%) for egg+ bait;
  • 288/330 (87.3%) for egg bait;
  • results were significant with p value being 0.002 and Chi² value being 10.10 (between intestine and egg baits);
  • results were also significant with the egg+ bait, p value was 0.04, Chi² value was 4.34).
• Intestine bait was swallowed more often than the egg and egg+ baits which did not allow for release of the vaccine into the oral cavity.

• Did not have means to evidence or assess objectively whether the animal had been successfully vaccinated.
• Vaccination teams directly involved in this study received limited training and had limited experience in approaching free-roaming dogs.
• Unequal distribution of each bait type, more dogs were offered intestine based baits rather than the other two types which may skew the results.
• Refused baits were collected and offered to the next dog, which would have altered the look, smell and shape of the bait potentially skewing results.

Free-roaming dogs in four urban and peri-urban districts of Bangladesh (in the Dhaka and Chittagong divisions).

356 dogs.

• As oral rabies vaccines (ORV) were not licensed in Bangladesh, placebo ORVs were used only.
• This study had three types of baits:
  
  
  • Fishmeal baits consisting of a block of vegetable fatty acids and fishmeal.
  • Intestine baits created from locally purchased cow intestine. Boiled for 5 minutes then cut into 8–10 cm segments.
  • Egg baits were made from egg powder and gelatin as described from the study from Bender et al. (2017).
• As this ORV study was conducted during a national rabies vaccination campaign, the ORV evaluators conducted this study 2–3 days after involvement in a capture-vaccinate-release programme.
  
  
  • The evaluator stood in the centroid of one of the four areas, and a simple random direction generator was used to complete a transect.
  • The evaluators were then given 60 baits and instructed to hand out at least 30 of the baits.
  • Six evaluators participated in total, all had multi-year experience interacting with free-roaming dogs through national vaccination campaigns.
  • Each evaluator was randomly assigned a bait type and then reassigned a different bait when moving to the next evaluation zone.
• Bait were all thawed before distribution.
• Baits were only offered to dogs that could be approached within a 3 metre distance, so that the bait could be thrown to the dogs.
• Dogs in crowded or unsafe locations such as a busy street were not selected.
• Dogs that were showing signs of aggression were also not offered bait.
• A mobile phone application was used to record the ORV data.

Non-blinded randomised control trial.

• When offered a bait, the evaluator recorded bait contact (‘showed interest’ or ‘ignored’), bait consumption, proportion of bait consumed (‘little’, ‘mostly’, or ‘complete’), and bait consumption time (recorded as the time elapsed between the dog being offered a bait and consuming it or losing interest, measured in time intervals (< 30, 30–60, 61–120 or > 120 seconds)).
• Dog characteristics including age, body condition, and temperament were also recorded.
  
  
  • Age was an estimation by the evaluator.
  • Temperament of the dog was determined at the discretion of the evaluator as well.
• Other factors were assessed:
  
  
  • temperament of the dog (either as ‘accessible’ [if report as friendly] or ‘inaccessible’ [if timid or aggressive]);
  • effectiveness (‘high-uptake’ or ‘low-uptake’);
  • characteristics of the inaccessible dogs who consume baits, bivariate and multivariable log-binomial regressions were conducted.
• Independent variables of interest:
  
  
  • bait attractants;
  • age;
  • body condition;
  • site type (urban or peri-urban).
• Binary dependent variable of interest was bait uptake.
  
  
  • Low-uptake baits were excluded from the analysis because and they were considered ineligible for future ORV campaigns.

• Of the three baits:
  
  
  • fish baits were ignored by 122/142 (86%) of dogs;
  • 45/75 (60%) consumed the egg bait;
  • 124/139 (89%)consumed the intestinal bait;
  • P value was < 0.05 meaning these results were significant.
• Among the consumed baits:
  
  
  • 10/18 (56%) of fish baits were fully consumed;
  • 38/45 (84%) of egg baits were fully consumed;
  • 122/124 (98%) of intestine baits were fully consumed; P value was < 0.05 meaning these results were significant.

• Perforation of the sachet for vaccine release into the oral cavity was not tested in this study which usually tests for the efficacy of the vaccine.
• A vaccine pack could have negatively modified bait odour and consistency and hence bait uptake might be overestimated.

CAB Direct on the CABI interface (1995–2023)
Web of Science on the Clarivate interface (2018–July 2023)

CAB Direct:
((("stray dog" OR "stray dogs" OR "strays" OR "free roaming" OR canine* OR canid*) AND (“egg based” OR egg Or “egg bait” OR bait) AND (“oral rabies vaccin*” OR “oral vaccin*”) AND (rabies OR lyssavirus*)))

Web of Science:
((((((((((((((((((((((((((((((((((TI=(stray dog)) OR TI=(stray dogs)) OR TI=(canine*)) OR TI=(free-roaming)) OR TI=(free roaming dog)) AND AB=(egg)) OR AB=(egg-based)) OR AB=(egg-based)) OR AB=(egg bait)) AND AB=(oral rabies vaccin*)) OR AB=(oral vaccin*)) AND AB=(rabies)) OR TS=(lyssavirus*)) AND AB=(uptake*)) OR AB=(preference)) OR AB=(eat)) OR AB=(consume)) NOT AB=(wildlife)) NOT AB=(bat*)) NOT AB=(owned)) NOT AB=(ownership)) NOT AB=(owner*)) NOT AB=(cat*)) NOT AB=(fox))) OR AB=(egg-based oral rabies vaccination)) OR AB=(bait acceptance)) OR ALL=(rabies control)) OR AB=(stray dog)) OR AB=(stray dogs)) OR TI=(free roaming )) OR TI=(free-roaming)) OR TI=(oral rabies vaccin*)) AND TI=(oral vaccin*)) NOT AB=(raccoon*)

21 Apr 2023

Articles not in English, literature that included dogs that were in any way owned and wildlife canidae, literature that did not cover rabies, published literature with no focus on bait preferences with oral rabies vaccination, literature that explored parenteral routes of administering the rabies vaccines, review, opinion or commentary papers.

Published paper on stray dog populations that had at least egg-based oral vaccinations and had results on preference rates of the bait, bait can be flavoured or made from raw food ingredient, oral vaccination was used as the basis of the intervention, literature was accessible and could be read in English and relevant to the PICO.