Dogs as vectors of rabies

While rabies is considered a relatively rare disease in developed countries, in much of the developing world it remains a serious health issue for humans. Two recent papers deal with dogs as vectors of rabies to humans.

Electron micrograph of the Rabies Virus. This electron 

micrograph shows the rabies virus - the small gray 

bodies, as well as Negri bodies, or cellular inclusions. 

CDC/Dr. Fred Murphy.

Aréchiga Ceballos et al. (2014) report that over 90% of human deaths from rabies worldwide are caused by dog bites. Mass vaccination, along with the effective control of dog populations, has been used successfully in industrialized countries to control this disease. However, a lower success rate in developing countries is due to a number of factors, including vaccination campaigns that do not cover a sufficient number of animals or reach all communities, and a wide biodiversity that increases the number of reservoirs of the rabies virus. Educational programs are needed, which focus on the commitment involved when acquiring a domestic animal, stating clearly what is required to provide it with a good quality of life. New technologies developed in the industrialized world will not always be successful in less developed countries. Approaches must be adapted to the particular conditions in each country, taking cultural and socio-economic issues into account. Authorities must promote research on dog population dynamics, the development of non-invasive methods to control dog populations and the most efficient, stable and low-cost options for vaccination. Under the One Health model, it is hoped that dog-transmitted human rabies will be accorded high priority as a zoonosis by human health authorities, international authorities and donor agencies to support ambitious eradication goals, particularly those being set in South-East Asia. Well-designed and adequately resourced vaccination programs, based on the World Organization for Animal Health (OIE) guidelines, will have significant animal welfare benefits, due to the availability of improved vaccines (in terms of efficacy, duration of immunity, ease of administration and lower cost), advances in dog population management and the more widespread implementation of the OIE Guidelines on stray Dog Control. Animal welfare benefits include not only the elimination of pain and suffering caused by the clinical disease itself, but also the avoidance of the indirect impact of inhumane culling when methods are used that have not been approved by the OIE.

In a second, recent paper on dogs and rabies Ajoke et al. (2014)  review the risk factors associated with dog trading and slaughtering dogs for food in the transmission of rabies in Nigeria. Emphasis on the potential role that the butchers play in rabies transmission and their susceptibility to rabies through contact with infectious meat samples and materials is also discussed. Dog meat has become a delicacy in many parts of Nigeria. It is eaten for various reasons including medicinal values, source of protein, and in rituals. Dogs are transported to the slaughter-houses for processing and they may have multiple origins. The rabies virus has been confirmed in apparently healthy dogs to be slaughtered showing that butchers are at risk, especially in Nigeria, where the butchers neither wear protective gear nor have they been vaccinated against rabies. The authors recommend regular vaccination for butchers and dogs. They conclude that dog trading, slaughtering and consumption probably play a major role in the epidemiology of rabies from dogs to humans in Nigeria.

Citation
Ajoke E., Solomon A, and Ikhide E. 2014. The role of dog trading and slaughter for meat in rabies epidemiology with special reference to Nigeria - a review. Journal of Experimental Biology and Agricultural Sciences, 2:130-136.

Aréchiga Ceballos N, Karunaratna D, Aguilar Setién 2014. Control of canine rabies in developing countries: key features and animal welfare implications. A Revue Scientifique et Technique (International Office of Epizootics)  33:311-321

Detection dogs and big cats

Greg Davidson and detection dog Chevy searching for cougar scat.

Detection dogs can be trained to locate explosives, illegal drugs, wildlife scat, or human remains. They have even been trained to locate illicit mobile phones in prisons. But, they have become extremely valuable for wildlife biologists and have been used to collect data on invasive species as well as endangered species.

In a forthcoming study in the Journal of Wildlife Management, Greg Davidson and colleagues from Find it Detection Dogs, used detection dogs to estimate the population size of cougars in northeast Oregon. Cougars are solitary, elusive, and have large home ranges. The researchers surveyed a 220 km² area using conservation detection dogs trained to locate cougar scat. Two hundred and seventy-two scat samples were collected, and 249 were analyzed for individual identification using DNA.  From 73 samples, 21 cougars (9 males and 12 females) could be recognized. The authors evaluated four models to estimate cougar densities: Huggins closed population capture–recapture (Huggins), CAPWIRE, multiple detections with Poisson (MDP), and spatially explicit capture–recapture (SECR). Their population estimates for the study area were 26 (9 males and 17 females) from Huggins models, 24 (9 males and 15 females) from CAPWIRE, and 27 (9 males and 18 females) from the MDP model.

This study demonstrates the efficacy of using detection dogs to collect cougar scat. The results suggest the probability of a dog finding a cougar’s scat on the landscape (given scat was available) in any of the 4 surveys was 0.99 for males and 0.68 for females. As a result, the authors were able to collected scat from all 4 GPS-collared cougars known to occupy a portion of the study area. The reported capture probabilities of this study were the largest observed for any previous study conducted with wild felids, which highlight the benefits of using scat detecting dogs to estimate cougar densities. Determining the age of the cougars captured was not possible because of the use of scat; so, their estimates included adults, subadults, and juveniles old enough to leave den sites.

Citation

Davidson, G. A., Clark, D. A., Johnson, B. K., Waits, L. P., & Adams, J. R. (in press, 2014). Estimating cougar densities in northeast Oregon using conservation detection dogs. The Journal of Wildlife Management. DOI: 10.1002/jwmg.758

H3N8 structure determined – canine influenza originated in horses

Canine influenza is a highly contagious respiratory infection of dogs caused by a novel influenza virus (H3N8) that was first discovered in 2004. Like influenza in other species, the canine influenza virus causes a cough, sneezing and nasal discharge. A fever may also occur, but it is usually transient and rarely noticed by dog owners. H3N8 cannot be distinguish from other respiratory infections without diagnostic tests.

All dogs exposed to H3N8 become infected; about 80% become ill, the other 20% show no symptoms. Recovery time is about two weeks but some dogs progress to pneumonia, which is usually due to secondary bacterial infections. While the mortality rate for canine influenza is very low, the secondary pneumonia can be life-threatening in some cases. Canine influenza is an emergent disease in dogs.

Collins et al. (2014) recently used x-ray crystallography to determine the structure of the H3 hemagglutinins (HAs) in two different equine viruses and the canine virus. They found all three are very similar in structure with the majority of amino acid sequence differences between the two equine HAs located on the virus membrane. HAs of canine viruses are distinct in containing the amino acid substitution Trp-222→Leu in the receptor binding site that influences specificity for the receptor. In the canine and recent equine virus HAs a unique difference is observed by comparison with all other HAs examined to date. Analyses of site-specific mutant HAs indicate that a single amino acid substitution, Thr-30→Ser, influences interactions between N-terminal and C-terminal regions of the subdomain that are important in the structural changes required for membrane fusion activity. Both structural modifications may have facilitated the transmission of H3N8 influenza from horses to dogs.

The authors summarized the situation as follows. Equine influenza viruses of the H3N8 subtype were first isolated in 1963 from race horses in Miami. Since then they have caused numerous outbreaks of infection in horses around the world with serious disease and economic consequences. In 2004, again in Florida, an H3N8 virus was isolated from an outbreak of canine influenza and similar viruses have since been isolated from dogs in the United States and in Europe. Genetic comparisons indicate that the canine viruses are closely related to equine viruses that were in circulation in horses around 2000. In studies of differences in equine viruses isolated since 1963 and between equine and canine viruses, the sequences of genes for the hemagglutinin membrane glycoprotein (HA) have been compared. Sequence data for equine virus HAs indicate the evolution of four distinct lineages. The first was associated with antigenic drift, between 1963 and 1980, and following this three separate branches formed a “Eurasian” lineage, an “American” lineage, and a divided lineage containing two clades, “Florida” clade 1 and Florida clade 2. The HAs of the canine viruses are most similar to those of Florida clade 1 equines. The majority of amino acid sequence changes revealed from the analyses are in the HA1 component of HA, some in regions known to be antigenically important in H3 HAs, and several near the receptor binding site.

The pdf is available on-line.

Citation

Collins, P. J.,  et al. (2014). Recent evolution of equine influenza and the origin of canine influenza. Proceedings of the National Academy of Sciences, 201406606.