System dynamics modelling approach to explore the effect of dog demography on rabies vaccination coverage in Africa

Using systems perspectives in evidence synthesis: A methodological mapping review

Reviewing complex interventions is challenging because they include many elements that can interact dynamically in a nonlinear manner. A systems perspective offers a way of thinking to help understand complex issues, but its application in evidence synthesis is not established. The aim of this project was to understand how and why systems perspectives have been applied in evidence synthesis. A methodological mapping review was conducted to identify papers using a systems perspective in evidence synthesis. A search was conducted in seven bibliographic databases and three search engines. A total of 101 papers (representing 98 reviews) met the eligibility criteria. Two categories of reviews were identified: (1) reviews using a "systems lens" to frame the topic, generate hypotheses, select studies, and guide the analysis and interpretation of findings (n = 76) and (2) reviews using systems methods to develop a systems model (n = 22). Several methods (e.g., systems dynamic modeling, soft systems approach) were identified, and they were used to identify, rank and select elements, analyze interactions, develop models, and forecast needs. The main reasons for using a systems perspective were to address complexity, view the problem as a whole, and understand the interrelationships between the elements. Several challenges for capturing the true nature and complexity of a problem were raised when performing these methods. This review is a useful starting point when designing evidence synthesis of complex interventions. It identifies different opportunities for applying a systems perspective in evidence synthesis, and highlights both commonplace and less familiar methods.

Lassa Virus Countermeasures

Lassa Fever (LF) is a viral hemorrhagic fever endemic in West Africa. LF begins with flu-like symptoms that are difficult to distinguish from other common endemic diseases such as malaria, dengue, and yellow fever making it hard to diagnose clinically. Availability of a rapid diagnostic test and other serological and molecular assays facilitates accurate diagnosis of LF. Lassa virus therapeutics are currently in different stages of preclinical development. Arevirumab, a cocktail of monoclonal antibodies, demonstrates a great safety and efficacy profile in non-human primates. Major efforts have been made in the development of a Lassa virus vaccine. Two vaccine candidates, MeV-NP and pLASV-GPC are undergoing evaluation in phase I clinical trials.

The effects of geographical distributions of buildings and roads on the spatiotemporal spread of canine rabies: An individual-based modeling study

Rabies is a fatal disease that has been a serious health concern, especially in developing countries. Although rabies is preventable by vaccination, the spread still occurs sporadically in many countries, including Thailand. Geographical structures, habitats, and behaviors of host populations are essential factors that may result in an enormous impact on the mechanism of propagation and persistence of the disease. To investigate the role of geographical structures on the transmission dynamics of canine rabies, we developed a stochastic individual-based model that integrates the exact configuration of buildings and roads. In our model, the spatial distribution of dogs was estimated based on the distribution of buildings, with roads considered to facilitate dog movement. Two contrasting areas with high- and low-risk of rabies transmission in Thailand, namely, Hatyai and Tepha districts, were chosen as study sites. Our modeling results indicated that the distinct geographical structures of buildings and roads in Hatyai and Tepha could contribute to the difference in the rabies transmission dynamics in these two areas. The high density of buildings and roads in Hatyai could facilitate more rabies transmission. We also investigated the impacts of rabies intervention, including reducing the dog population, restricting owned dog movement, and dog vaccination on the spread of canine rabies in these two areas. We found that reducing the dog population alone might not be sufficient for preventing rabies transmission in the high-risk area. Owned dog confinement could reduce more the likelihood of rabies transmission. Finally, a higher vaccination coverage may be required for controlling rabies transmission in the high-risk area compared to the low-risk area.

Free-roaming dog population dynamics in Ranchi, India

Rabies causes approximately 20,000 human deaths in India each year. Nearly all of these occur following dog bites. Large-scale, high-coverage dog rabies vaccination campaigns are the cornerstone of rabies elimination strategies in both human and dog populations, although this is particularly challenging to achieve in India as a large proportion of the dog population are free-roaming and unowned. Further, little is known about free-roaming dog ecology in India which makes defining optimum vaccination strategies difficult. In this study, data collected using a mobile phone application during three annual mass vaccination and neutering (surgical sterilisation of both males and females) campaigns of free-roaming dogs in Ranchi, India (during which a total of 43,847 vaccinations, 26,213 neuter surgeries and 28,172 re-sight observations were made) were interrogated, using two novel approaches to estimate the proportion of neutered dogs that were lost from the city (assumed due to mortality or migration) between campaign years. Analysis revealed high losses of neutered dogs each year, ranging from 25.3% (28.2-22.8) to 55.8% (57.0-54.6). We also estimated that the total population declined by 12.58% (9.89-15.03) over the three-year period. This demonstrates that there is a high turnover of free-roaming dogs and that despite neutering a large number of dogs in an annual sterilisation campaign, the decline in population size was modest over a three-year time period. These findings have significant implications for the planning of rabies vaccination campaigns and population management programmes as well as highlighting the need for further research into the demographics of free-roaming, unowned dogs in India.

Evaluation of dog vaccination schemes against rabies in Kinshasa, Democratic Republic of the Congo

The traditional rabies control strategy based on annual mass vaccination of dogs appears to be costly and cumbersome. Given the existence of different risk zones for rabies transmission, the present study aimed at proposing risk-based vaccination schemes by considering canine population dynamics as well as vaccine efficacy and duration of immunity (DOI). The capital of the Democratic Republic of the Congo (RDC), Kinshasa, was chosen as study site. The turnover rate of dogs was used to assess their population dynamics in two low-roaming (<25 % of dogs are roaming) and in two high-roaming zones (>75 % of dogs are roaming). The sero-conversion rate was assessed in response to primo-vaccination in three age groups: 24 puppies (≤3months), 37 juveniles (4-12 months) and 22 adult dogs. The DOI was evaluated serologically by revaccinating dogs previously vaccinated since 1-2 years (n = 31), 2-3 years (n = 12) or 3-7.5 years (n = 4). Rapid Fluorescent Focus Inhibition Test was used to quantify antibodies. These data were used to implement vaccination outcome models.The turnover rate was twice as high in high-roaming zones (36 %) as that in lowroaming zones (17 %). Irrespective of roaming level, 75 % of dogs were less than 3 years old. The vaccine was equally effective in puppies (96 %), juvenile (97 %) and adult dogs (100 %, p = 0.24). The vaccine was effective in 93 % (11/12) of puppies without pre-vaccinal protective titers (≥0.5 IU/mL). The anamnestic response was strong within 5-8 days upon the booster vaccination, in 96 % (45/47) of dogs reported vaccinated 1-7.5 years before. This suggests that the vaccine provided a long-term protection (≥3 years) which is likely to occur in 75 % of dogs in Kinshasa.Hypothesizing a vaccination stop, the vaccination outcome model allowed to estimate the time point after which vaccination coverage would drop below 40 % in function of dog population turnover rate. The systematic vaccination of puppies as well as annual vaccination of dogs aged between 3 and 15 months or annual vaccination of all unvaccinated dogs aged more than 3 months of age appeared as valuable alternative to systematic annual mass vaccination.In conclusion, this study developed a vaccination outcome model pointing out the impact of dog population dynamics and of effective duration of immunity. It appears as a promising tool for designing cost-effective rabies vaccination campaigns.

Tetravalent Rabies-Vectored Filovirus and Lassa Fever Vaccine Induces Long-term Immunity in Nonhuman Primates

BACKGROUND

The objective of this study is to evaluate the immunogenicity of adjuvanted monovalent rabies virus (RABV)-based vaccine candidates against Ebola virus (FILORAB1), Sudan virus (FILORAB2), Marburg virus (FILORAB3), Lassa virus (LASSARAB1), and combined trivalent vaccine candidate (FILORAB1-3) and tetravalent vaccine candidate (FILORAB1-3 and LASSARAB) in nonhuman primates.

METHODS

Twenty-four Macaca fascicularis were randomly assigned into 6 groups of 4 animals. Each group was vaccinated with either a single adjuvanted vaccine, the trivalent vaccine, or the tetravalent vaccine at days 0 and 28. We followed the humoral immune responses for 1 year by antigen-specific enzyme-linked immunosorbent assays and RABV neutralization assays.

RESULTS

High titers of filovirus and/or Lassa virus glycoprotein-specific immunoglobulin G were induced in the vaccinated animals. There were no significant differences between immune responses in animals vaccinated with single vaccines vs trivalent or tetravalent vaccines. In addition, all vaccine groups elicited strong rabies neutralizing antibody titers. The antigen-specific immune responses were detectable for 1 year in all groups.

CONCLUSIONS

In summary, this study shows the longevity of the immune responses up to 365 days for a pentavalent vaccine-against Ebola virus, Sudan virus, Marburg virus, Lassa virus, and RABV-using a safe and effective vaccine platform.

[New aspects of rabies control]

Rabies still causes about 60,000 human deaths per year, mainly in poor populations in Africa and Asia. However, since Louis Pasteur developed the first vaccine 130 years ago, prophylactic measures have been considerably improved and simplified. They now consist of the vaccine combined with purified rabies immunoglobulins of equine or human origin. In general, however, post-exposure prophylaxis protocols are long and expensive. Furthermore, the immunoglobulins used for associated serotherapy are costly and not widely available in developing countries. Approaches have been developed to deal with these two issues that offer hope for a paradigm shift for the benefit of exposed populations. Finally, mass rabies vaccination in dogs, which are the most cost-effective measure for preventing rabies in humans, are difficult to implement and sometimes have moderate effectiveness. The identification and analysis of the epidemiological drivers conditioning the circulation of the virus in dog populations allow a better understanding of the key control points that need to be associated with these campaigns for a better efficacy.

Prevalence of Toxocara in dogs and cats in Africa

Dogs and cats have a close association with humans providing companionship; however, pets are reservoirs of zoonotic pathogens such as Toxocara. Toxocara canis and Toxocara cati are small intestinal nematodes found in canids and felids, respectively. Infected pets shed thousands of eggs resulting in environmental contamination. Toxocara can infect a wide variety of paratenic hosts including humans, rodents, pigs and chickens. Paratenic hosts become infected by ingestion of the infective eggs containing the third stage larvae or ingestion of dormant larvae in animal tissues. Infected humans may develop visceral larval migrans or ocular toxocariasis. Regular anthelmintic treatment and restricted movement of dogs and cats are recommended to control Toxocara environmental contamination. This paper reviews the prevalence and risk factors of Toxocara in dogs and cats in Africa; and pet owners' awareness of canine zoonotic helminths.

Modelling targeted rabies vaccination strategies for a domestic dog population with heterogeneous roaming patterns

Australia is currently canine rabies free. However, communities located on the northern coastline-such as the Northern Peninsula Area (NPA), Queensland-are at risk of an incursion due to their large populations of susceptible free-roaming dogs and proximity to rabies-infected Indonesian islands. A rabies-spread model was used to simulate potential outbreaks and evaluate various disease control strategies. A heterogeneous contact structure previously described in the population of interest-explorer dogs, roamer dogs and stay-at-home dogs-was incorporated into the model using six spatial kernels describing contacts between dog roaming categories. Twenty-seven vaccination strategies were investigated based on a complete block design of 50%, 70% and 90% coverage for each of the three roaming categories to simulate various targeted vaccination strategies. The 27 strategies were implemented in four population structures in which the proportion of dogs in each category varied-explorer dominant, roamer dominant, stay-at-home dominant and a field population (based on field estimates of population structure). The overall vaccination coverage varied depending on the subpopulation targeted for vaccination and the population structure modelled. A total of 108 scenarios were simulated 2000 times and the model outputs (outbreak size and duration) were compared to Strategy 14 (a standard recommended overall 70% vaccination coverage). In general, targeting explorer dogs-and to a lesser extent roamer dogs-produced similar outbreaks to Strategy 14 but with a lower overall vaccination coverage. Similarly, strategies that targeted stay-at-home dogs required a higher vaccination coverage to produce significantly smaller and shorter outbreaks. This study provides some theoretical evidence that targeting subpopulations of dogs for vaccination based on their roaming behaviours (and therefore risk of rabies transmission) could be more efficient than blanket 70% vaccination campaigns. Such information can be used in preparedness planning to help improve control of a potential rabies incursion in Australia.