Detection of rabies antibody by ELISA and RFFIT in unvaccinated dogs and in the endangered Simien jackal (Canis simensis) of Ethiopia

Incidence and seroprevalence of rabies virus in humans, dogs and other animal species in Africa, a systematic review and meta-analysis

Rabies is transmitted to humans mainly by dogs but also by other animal species. Reliable data on the incidence of Rabies virus (RABV) in humans, dogs, and other animal species in Africa, could be essential in the implementation of a global strategic plan to eliminate the RABV by 2030 as adopted by the WHO, OIE, and FAO. We searched the Pubmed, Embase, Scopus, African Journal Online, and African Index Medicus databases for relevant studies that report data on the incidence of RABV in Africa up to February 17, 2020. Information on active and past RABV exposures in various categories of dogs, humans and other animal species were extracted. Incidence and seroprevalence estimates were pooled using a random-effect meta-analysis. We included 73 articles which provided 142 RABV incidence and seroprevalence records in 21 African countries. The estimated incidence of RABV in 222 humans, 15,600 dogs, and 12,865 other animal species was 83.4% (95% CI = 64.6–96.5), 44.1% (95% CI = 35.1–53.4), and 41.4% (95% CI = 29.6–53.8), respectively. The estimated seroprevalence of RABV in 420 humans, 3577 dogs, and 8,55 other animal species was 33.8% (95% CI = 21.9–46.8), 19.8% (95% CI = 13.3–27.3), and 3.6% (95% CI = 0.3–9.2), respectively. The incidence of RABV in general was higher in suspected rabid dogs, other animal species of the Orders Perissodactyla, Artiodactyla and Carnivora. The incidence of RABV was higher for humans in regions of West and East Africa, for dogs in urban areas and in regions of Central and South Africa, and for animals of the order Perissodactyla in urban areas. This meta-analysis demonstrated a high incidence of RABV in Africa. Itis necessary to improve surveillance system to provide reliable data on RABV in Africa, essential for the implementation of an effective control strategy.

Rabies virus-neutralising antibodies in healthy, unvaccinated individuals: What do they mean for rabies epidemiology?

Rabies has been a widely feared disease for thousands of years, with records of rabid dogs as early as ancient Egyptian and Mesopotamian texts. The reputation of rabies as being inevitably fatal, together with its ability to affect all mammalian species, contributes to the fear surrounding this disease. However, the widely held view that exposure to the rabies virus is always fatal has been repeatedly challenged. Although survival following clinical infection in humans has only been recorded on a handful of occasions, a number of studies have reported detection of rabies-specific antibodies in the sera of humans, domestic animals, and wildlife that are apparently healthy and unvaccinated. These 'seropositive' individuals provide possible evidence of exposure to the rabies virus that has not led to fatal disease. However, the variability in methods of detecting these antibodies and the difficulties of interpreting serology tests have contributed to an unclear picture of their importance. In this review, we consider the evidence for rabies-specific antibodies in healthy, unvaccinated individuals as indicators of nonlethal rabies exposure and the potential implications of this for rabies epidemiology. Our findings indicate that whilst there is substantial evidence that nonlethal rabies exposure does occur, serology studies that do not use appropriate controls and cutoffs are unlikely to provide an accurate estimate of the true prevalence of nonlethal rabies exposure.

The Ethiopian wolf – an endangered endemic canid

The Ethiopian wolf is a social canid endemic to the highlands of Ethiopia. Today perhaps only 500 individuals survive, making it the world's rarest and probably most endangered canid. Its range has already been reduced and it is threatened by further loss of habitat to high-altitude subsistence agriculture and overgrazing by livestock. Today it survives in only six locations, with the largest and probably only genetically viable population being found in the Bale Mountains National Park. The most immediate threats for the survival of Ethiopian wolves are disease, domestic dogs and human persecution. Improved management in Bale and Simien Mountains National Parks and the establishment of a captive-breeding programme are urgently needed to prevent the extinction of this species.

Rabies in small animals

Rabies in small animals has been dramatically reduced in the United States since the introduction of rabies vaccination of domestic animals in the 1940s. As a consequence, the number of human rabies cases has declined to only a couple per year. During the past several years, the dog rabies variant has almost disappeared completely. Rabies in wildlife has skyrocketed, however. Each wildlife species carries its own rabies variant(s). These wildlife epizootics present a constant public health threat in addition to the danger of reintroducing rabies to domestic animals. Vaccination is the key to prevent rabies in small animals and rabies transmission to human beings.

Clinical laboratory advances in the detection of rabies virus

Rabies is one of the most feared zoonotic diseases in the world. All warm-blooded animals are susceptible to infection by the virus, but the main vectors of human infection are dogs and cats. Development of rabies can be prevented by postexposure vaccination, and with a few exceptions, the exact time and source of human infection is usually known. However, the effective use of postexposure vaccination depends on the rapid and accurate detection of rabies virus in specimens obtained from the source of human infection. This paper provides an overview on developments on laboratory methods for the early detection of rabies virus. In most laboratories, the fluorescent antibody test (FAT) is used as the most important primary test, with the rabies tissue culture infection test (RTCIT) or the mouse inoculation test (MIT) being used as confirmatory backup procedures. However, other methods for the detection of antigens, such as rapid rabies-specific enzyme-linked immunosorbent assay (rapid-ELISA) and the detection of viral nucleic acids by reverse transcription polymerase chain reaction (RT-PCR) are increasingly being used for diagnosis and, in combination with nucleotide sequencing, for epidemiological investigations.

Regular exposure to rabies virus and lack of symptomatic disease in Serengeti spotted hyenas

We report a previously unrecognized complexity to the ecology of rabies in wildlife. Rabies-specific virus-neutralizing antibodies in spotted hyenas, the most numerous large carnivore in the Serengeti ecosystem (Tanzania, East Africa), revealed a high frequency of exposure of 37.0% to rabies virus, and reverse transcriptase (RT) PCR demonstrated rabies RNA in 13.0% of hyenas. Despite this high frequency, exposure neither caused symptomatic rabies nor decreased survival among members of hyena social groups monitored for 9 to 13 years. Repeated, intermittent presence of virus in saliva of 45.5% of seropositive hyenas indicated a "carrier" state. Rabies isolates from Serengeti hyenas differed significantly (8.5% sequence divergence) from those isolated from other Serengeti carnivores, suggesting that at least two separate strains circulate within the Serengeti carnivore community. This finding is consistent with the fact that exposure in hyenas increased with age and social status, following a pattern predicted by intraspecific age and social-status-dependent oral and bite contact rates. High seroprevalence of rabies, low basic reproductive rate of the virus (R(0)) of 1.9, a carrier state, and the absence of symptomatic rabies in a carnivore in an ecosystem with multihost and multistrain maintenance has not been previously demonstrated for rabies. Because of the substantial differences between the hyena viral isolates and those from canids and viverrids in the Serengeti, it is unlikely that spotted hyenas were the source of rabies virus that killed several African wild dog packs in the Serengeti ecosystem in the 1990s.

Dog ecology and demography information to support the planning of rabies control in Machakos District, Kenya

A study of 150 dog-owning households from six randomly selected sublocations was conducted in Machakos District, Kenya. Initially, all households were visited to collect information on dog ecology and demography based on WHO guidelines and to collect serum for rabies antibody detection. A second visit was made 1 year later, to obtain follow-up data on births, deaths, dog movements and other events since the first visit. Dog ownership was common, with a range of 53--81% (mean=63%) of households owning dogs in the six sublocations. Dog density for the five more rural sublocations ranged from 6 to 21 dogs km(-2) and for the peri-urban sublocation was 110 dogs km(-2). The dog population was estimated to be growing at 9% p.a. (95% C.I. 4--14%). This growth was a function of very high fecundity (1.3 females per female per year) more than compensating for high mortality, particularly among females. Life expectancy from birth was 3.5 years for males and 2.4 years for females. Half the dogs at any one time were less than 1 year of age. All dogs, by design of the study, were owned. Of these, 69% were never restricted and roamed freely to forage for food and mix with other dogs. Only a small proportion of dogs (5%) were fed commercial dog food. Most households reported observing dogs scavenging their garbage, including: their own dogs (81%), their neighbours' dogs (75%) and unknown dogs (45%). Only 29% of dogs at least 3 months of age were reported to be vaccinated against rabies. The proportion vaccinated varied widely between sublocations (5--68%); 48% of dogs reportedly vaccinated had detectable antibodies, 31% at or above levels considered to indicate seroconversion. The proportion of dogs with detectable antibodies declined according to the time since last vaccination (55% if vaccinated < or = 1 year, 47% < or = 2 years and 36% > 2 years); 20% of dogs reported not to have been vaccinated had detectable rabies antibody. Compared to other dog populations in rural eastern and southern Africa, Machakos District has a high density of dogs. The Machakos dog population is growing, highly dynamic, poorly supervised and inadequately vaccinated against rabies. The main implication for rabies control is that adequate vaccination coverage is unlikely to be achieved, even under optimal delivery, using the current strategy of annual vaccination of dogs older than 3 months.

Maintenance of a microparasite infecting several host species: rabies in the Serengeti

Whether and how microparasites such as rabies persist in their host populations are among the fundamental questions of infectious disease epidemiology. Rabies is fatal disease of all mammalian species, but not all mammalian species can maintain the infection as reservoirs. The approach to control depends on which of the affected species do act as reservoirs. Bringing together old and new data, we examine here the role of wild and domestic animals in maintaining rabies in the Serengeti region of Tanzania, presenting our findings in two parts. In Part I, we argue that domestic dogs are the likely reservoirs because: (1) rabies has been continuously present in the dog population since its (re)introduction in 1977, whilst (2) wildlife cases have been very rare over this period, despite intensive study of Serengeti carnivores; (3) outbreaks of rabies in wild canids (jackals) elsewhere in Africa (Zimbabwe) have followed, rather than preceded, outbreaks in the dog population; (4) all viruses isolated from wild carnivores in the Serengeti ecosystem (including the Kenyan Masai Mara) are antigenically and genetically indistinguishable from the typical domestic dog strain; (5) dog rabies control in the Serengeti between 1958-77 apparently eliminated the disease from both dogs and wildlife. Having identified dogs as reservoirs, Part II explores some possible mechanisms of maintenance in dog populations. In theory, infection is more likely to be maintained at higher dog densities, and we provide evidence that rabies is maintained in one district with a dog density > 5/km2, but not in two other districts with densities < 1/km2. Because 5 dogs/km2 is much lower than the expected density required for persistence, we go on to investigate the role of atypical infections, showing: (1) from serology, that a substantial proportion of healthy dogs in the Serengeti have detectable serum levels of rabies-specific antibody; (2) from mathematical models that, whilst we cannot be sure what seropositivity means, persistence in low-density dog populations is more likely if seropositives are infectious carriers, rather than slow-incubators or immunes.

A liquid-phase blocking ELISA for the detection of antibodies to rabies virus

A liquid-phase blocking ELISA was adapted to the detection and titration of antibodies to principally the nucleoprotein of rabies virus. Sera from animals that had either been vaccinated against rabies or inoculated with street rabies viruses, as well as sera from animals that had no recorded contact with rabies, were tested. These included sera from people, cattle, sheep, goats, dogs, laboratory mice, rabbits, yellow mongooses, wild dogs and lions. Where possible, the results were compared with those obtained with a commercial kit incorporating an indirect ELISA that measures antibody to the rabies glycoprotein. There was a high correlation (r = 0.79) between the two tests. The blocking ELISA provides a single test suitable for the rapid detection of antibodies against rabies virus in the sera of any animal species and for that reason is particularly apt for epidemiological investigations in regions where species diversity is important, as in southern Africa.

Molecular genetics of the most endangered canid: the Ethiopian wolf Canis simensis

The world's most endangered canid is the Ethiopian wolf Canis simensis, which is found in six isolated areas of the Ethiopian highlands with a total population of no more than 500 individuals. Ethiopian wolf populations are declining due to habitat loss and extermination by humans. Moreover, in at least one population, Ethiopian wolves are sympatric with domestic dogs, which may hybridize with them, compete for food, and act as disease vectors. Using molecular techniques, we address four questions concerning Ethiopian wolves that have conservation implications. First, we determine the relationships of Ethiopian wolves to other wolf-like canids by phylogenetic analysis of 2001 base pairs of mitochondrial DNA (mtDNA) sequence. Our results suggest that the Ethiopian wolf is a distinct species more closely related to gray wolves and coyotes than to any African canid. The mtDNA sequence similarity with gray wolves implies that the Ethiopian wolf may hybridize with domestic dogs, a recent derivative of the gray wolf. We examine this possibility through mtDNA restriction fragment analysis and analysis of nine microsatellite loci in populations of Ethiopian wolves. The results imply that hybridization has occurred between female Ethiopian wolves and male domestic dogs in one population. Finally, we assess levels of variability within and between two Ethiopian wolf populations. Although these closely situated populations are not differentiated, the level of variability in both is low, suggesting long-term effective population sizes of less than a few hundred individuals. We recommend immediate captive breeding of Ethiopian wolves to protect their gene pool from dilution and further loss of genetic variability.