The feasibility of canine rabies elimination in Africa: dispelling doubts with data

The implications of metapopulation dynamics on the design of vaccination campaigns

Control programmes for vaccine preventable diseases typically operate under logistic constraints such as limited resources and in spatially structured populations where the assumption of homogeneous mixing is invalid. It is unclear, therefore, how to maximise the effectiveness of campaigns in such populations. We investigate how to deploy vaccine in metapopulations by comparing the effectiveness of alternative vaccination strategies on reducing disease occurrence (presence/absence), using canine rabies as a model system, and a domestic dog population within a Tanzanian district divided into sub-populations corresponding to villages. We use patch-occupancy models to quantify the contribution of sub-populations to disease occurrence ("risk") and model allocation strategies for a limited number of vaccine doses that prioritize villages based on their size, risk, or the reduction in risk for the entire population that would result from vaccination. We assume that a maximum of 70% of susceptible individuals in a village could be vaccinated, and that only susceptible dogs are vaccinated. The most effective strategy maximised the reduction in risk of the entire population, and was up to 62% more effective than the other strategies. Large, single-pulse campaigns provided the greatest short-term protection, but higher frequencies of smaller pulses were more effective at reducing long-term disease occurrence. Vaccine allocation on a per-dose basis was substantially more effective than a per-village strategy, indicating that operational constraints can reduce control effectiveness. The spatial distribution and abundance of hosts have an important influence on disease dynamics and these results demonstrate that metapopulation models can be used to substantially improve the effectiveness of vaccination campaigns and optimize the allocation of limited control resources.

Newcastle disease virus-vectored rabies vaccine is safe, highly immunogenic, and provides long-lasting protection in dogs and cats

Effective, safe, and affordable rabies vaccines are still being sought. Newcastle disease virus (NDV), an avian paramyxovirus, has shown promise as a vaccine vector for mammals. Here, we generated a recombinant avirulent NDV La Sota strain expressing the rabies virus glycoprotein (RVG) and evaluated its potential to serve as a vaccine against rabies. The recombinant virus, rL-RVG, retained its high-growth property in chicken eggs, with titers of up to 10⁹·⁸ 50% egg infective doses (EID₅₀)/ml of allantoic fluid. RVG expression enabled rL-RVG to spread from cell to cell in a rabies virus-like manner, and RVG was incorporated on the surface of the rL-RVG viral particle. RVG incorporation did not alter the trypsin-dependent infectivity of the NDV vector in mammalian cells. rL-RVG and La Sota NDV showed similar levels of sensitivity to a neutralization antibody against NDV and similar levels of resistance to a neutralization antibody against rabies virus. Animal studies demonstrated that rL-RVG is safe in several species, including cats and dogs, when administered as multiple high doses of recombinant vaccine. Intramuscular vaccination with rL-RVG induced a substantial rabies virus neutralization antibody response and provided complete protection from challenge with circulating rabies virus strains. Most importantly, rL-RVG induced strong and long-lasting protective neutralization antibody responses to rabies virus in dogs and cats. A low vaccine dose of 10⁸·³ EID₅₀ completely protected dogs from challenge with a circulating strain of rabies virus for more than a year. This is the first study to demonstrate that immunization with an NDV-vectored vaccine can induce long-lasting, systemic protective immunity against rabies.

Renewed global partnerships and redesigned roadmaps for rabies prevention and control

Canine rabies, responsible for most human rabies deaths, is a serious global public health concern. This zoonosis is entirely preventable, but by focusing solely upon rabies prevention in humans, this “incurable wound” persists at high costs. Although preventing human deaths through canine rabies elimination is feasible, dog rabies control is often neglected, because dogs are not considered typical economic commodities by the animal health sector. Here, we demonstrate that the responsibility of managing rabies falls upon multiple sectors, that a truly integrated approach is the key to rabies elimination, and that considerable progress has been made to this effect. Achievements include the construction of global rabies networks and organizational partnerships; development of road maps, operational toolkits, and a blueprint for rabies prevention and control; and opportunities for scaling up and replication of successful programs. Progress must continue towards overcoming the remaining challenges preventing the ultimate goal of rabies elimination.

Evolutionary history of rabies in Ghana

Rabies virus (RABV) is enzootic throughout Africa, with the domestic dog (Canis familiaris) being the principal vector. Dog rabies is estimated to cause 24,000 human deaths per year in Africa, however, this estimate is still considered to be conservative. Two sub-Saharan African RABV lineages have been detected in West Africa. Lineage 2 is present throughout West Africa, whereas Africa 1a dominates in northern and eastern Africa, but has been detected in Nigeria and Gabon, and Africa 1b was previously absent from West Africa. We confirmed the presence of RABV in a cohort of 76 brain samples obtained from rabid animals in Ghana collected over an eighteen-month period (2007-2009). Phylogenetic analysis of the sequences obtained confirmed all viruses to be RABV, belonging to lineages previously detected in sub-Saharan Africa. However, unlike earlier reported studies that suggested a single lineage (Africa 2) circulates in West Africa, we identified viruses belonging to the Africa 2 lineage and both Africa 1 (a and b) sub-lineages. Phylogeographic Bayesian Markov chain Monte Carlo analysis of a 405 bp fragment of the RABV nucleoprotein gene from the 76 new sequences derived from Ghanaian animals suggest that within the Africa 2 lineage three clades co-circulate with their origins in other West African countries. Africa 1a is probably a western extension of a clade circulating in central Africa and the Africa 1b virus a probable recent introduction from eastern Africa. We also developed and tested a novel reverse-transcription loop-mediated isothermal amplification (RT-LAMP) assay for the detection of RABV in African laboratories. This RT-LAMP was shown to detect both Africa 1 and 2 viruses, including its adaptation to a lateral flow device format for product visualization. These data suggest that RABV epidemiology is more complex than previously thought in West Africa and that there have been repeated introductions of RABV into Ghana. This analysis highlights the potential problems of individual developing nations implementing rabies control programmes in the absence of a regional programme.

An ecological and conservation perspective on advances in the applied virology of zoonoses

The aim of this manuscript is to describe how modern advances in our knowledge of viruses and viral evolution can be applied to the fields of disease ecology and conservation. We review recent progress in virology and provide examples of how it is informing both empirical research in field ecology and applied conservation. We include a discussion of needed breakthroughs and ways to bridge communication gaps between the field and the lab. In an effort to foster this interdisciplinary effort, we have also included a table that lists the definitions of key terms. The importance of understanding the dynamics of zoonotic pathogens in their reservoir hosts is emphasized as a tool to both assess risk factors for spillover and to test hypotheses related to treatment and/or intervention strategies. In conclusion, we highlight the need for smart surveillance, viral discovery efforts and predictive modeling. A shift towards a predictive approach is necessary in today's globalized society because, as the 2009 H1N1 pandemic demonstrated, identification post-emergence is often too late to prevent global spread. Integrating molecular virology and ecological techniques will allow for earlier recognition of potentially dangerous pathogens, ideally before they jump from wildlife reservoirs into human or livestock populations and cause serious public health or conservation issues.

Animal contact as a source of human non-typhoidal salmonellosis

Non-typhoidal Salmonella represents an important human and animal pathogen world-wide. Most human salmonellosis cases are foodborne, but each year infections are also acquired through direct or indirect animal contact in homes, veterinary clinics, zoological gardens, farm environments or other public, professional or private settings. Clinically affected animals may exhibit a higher prevalence of shedding than apparently healthy animals, but both can shed Salmonella over long periods of time. In addition, environmental contamination and indirect transmission through contaminated food and water may complicate control efforts. The public health risk varies by animal species, age group, husbandry practice and health status, and certain human subpopulations are at a heightened risk of infection due to biological or behavioral risk factors. Some serotypes such as Salmonella Dublin are adapted to individual host species, while others, for instance Salmonella Typhimurium, readily infect a broad range of host species, but the potential implications for human health are currently unclear. Basic hygiene practices and the implementation of scientifically based management strategies can efficiently mitigate the risks associated with animal contacts. However, the general public is frequently unaware of the specific disease risks involved, and high-risk behaviors are common. Here we describe the epidemiology and serotype distribution of Salmonella in a variety of host species. In addition, we review our current understanding of the public health risks associated with different types of contacts between humans and animals in public, professional or private settings, and, where appropriate, discuss potential risk mitigation strategies.

Experimental rabies vaccines for humans

Rabies remains a global public health threat that kills more than 55,000 people per year. Rabies disproportionately affects children and, therefore, is ranked the seventh most important infectious disease due to years lost. Prevention of human rabies is accomplished by controlling rabies in domestic and wild animals, including the use of vaccination programs. The usefulness of human rabies vaccines is hampered by high cost, complicated vaccination regimens and lack of compliance, especially in areas of Africa and Asia where human rabies infections are endemic. A single-dose vaccine would greatly benefit efforts to combat this global health threat. However, a single-dose vaccine based on current inactivated vaccines does not appear feasible and other approaches are needed. Technology has advanced since modern human rabies vaccines were developed over 40 years ago. In addition, our understanding of immunological principles that influence the outcome of vaccination has increased. This article describes the current status of inactivated rabies virus vaccines and recent developments arising from the use of reverse genetics technologies designed to develop replication-deficient or single-cycle live rabies virus-based vectors for use as a single-dose rabies vaccine for humans.

Biting back against rabies

World Rabies Day, on 28 September, focuses our attention on a horrific, preventable disease that still kills tens of thousands of people each year.

World Rabies Day, on 28 September, focuses our attention on a horrific, preventable disease that still kills tens of thousands of people each year.

Rabies and African bat lyssavirus encephalitis and its prevention

Unlike any other human infection, encephalitis caused by dog rabies virus is always fatal. Rabies and other lyssaviruses have been found in unexpected places, and human disease, especially paralytic rabies, has gone unrecognised. Evidence is emerging that rabies-related bat lyssaviruses are enzootic across Europe, Africa, Asia and Australia, but none has been detected in the Americas. The epidemiology and origins of African lyssaviruses are discussed. Ideal rabies prophylaxis (pre-exposure immunisation followed by post-exposure booster vaccination) has proved 100% effective; hence all human deaths result from failure of prevention. Rabies vaccines of known quality are unaffordable for the majority in Africa. Although intradermal regimens requiring <40% of the usual vaccine dose are economical and are recommended by the World Health Organization, several problems have inhibited their use. A new, simplified, economical post-exposure vaccine regimen that uses an initial dose of intradermal injections at four sites overcomes many of the difficulties of the previous methods: it is at least as immunogenic as the standard intramuscular course of tissue-culture vaccine; is safer in inexperienced hands; requires fewer than two ampoules of vaccine and only three instead of five clinic visits. Recent data should increase the confidence of physicians to use the World Health Organization-accredited rabies vaccines more efficiently and at lower cost.