Oral vaccine achieves up to 78% immunization of dogs who cannot otherwise be vaccinated
WINDHOEK, Namibia––The Namibian Ministry of Agriculture, Water & Land Reform on November 11, 2021 told the Chinese national news agency Xinhua that it had successfully completed a first field trial of an oral rabies vaccine for dogs.
The Namibian field trial appears to be the first claimed success of oral vaccination against canine rabies in the southern hemisphere, and could be a major step toward achieving eradication of canine rabies worldwide without killing dogs who cannot be captured for conventional immunization using injectable vaccines.
Conducted in mid-October 2021, the field trial vaccinated dogs against rabies in the northern Omusati and Oshana regions of Namibia, the Ministry of Agriculture, Water & Land Reform said.
Both locales are part of what is called the Northern Communal Area, just south of the Angolan border.
Conventional vaccination missed one dog in four
“Rabies is endemic throughout Namibia,” the Xinhua report explained. “However, dog-mediated rabies poses a significant threat to public health in the Northern Communal Area.”
Conventional vaccination by inoculation “could only attain about 76% vaccination coverage of total dog population in the Northern Communal Areas, instead of the targeted 80% vaccination coverage to achieve herd immunity,” explained Ministry of Agriculture, Water & Land Reform chief veterinary officer Albertina Shilongo.
“Oral vaccination will enable us to reach most, if not all dogs, especially stray dogs and dogs who are difficult to handle,” continued Shilongo.
“This new methodology, if fully introduced, will not replace our initial national dog rabies control program,” using standard injectable vaccines, “but will complement the parenteral vaccination for wider dog population reach,” Shilongo said.
“This first trial was carried out,” reported the Xinhua news service, “in close cooperation with the Friedrich-Loeffler Institute of Germany, supported with funds from the Global Health Protection Program of the German Ministry of Health, using mobile planning and data-capturing technology.”
Oral rabies vaccines never before effective in dogs
Commented Program for Monitoring Emerging Diseases moderator Arnon Shimshony, “Numerous control measures have been successful at eliminating dog-mediated human rabies deaths in humans is a very affluent nations, including dog population management, parenteral dog vaccination programs, access to human rabies vaccines, and education programs for bite prevention and wound treatment.
“Implementing these techniques in resource-poor settings,” however, “can be challenging; perhaps the greatest challenge is maintaining adequate herd immunity in free-roaming dog populations.
“Oral rabies vaccines have been a cornerstone in rabies virus elimination from wildlife
populations,” Shimshony acknowledged. “However, oral vaccines have never been effectively used to control dog-mediated rabies.”
Rabies vaccines are temperature sensitive
This has chiefly been because rabies vaccines, including those successfully used against fox, raccoon, skunk, and canine rabies in the northern hemisphere, tend to be extremely temperature-sensitive. Any break in the “cold chain” of refrigeration before administration tends to render both conventional injectable rabies vaccines and oral rabies vaccines ineffective.
Vaccinating canine rabies out of existence in much of the relatively cold northern hemisphere was accomplished long before oral rabies vaccinations were first developed and deployed.
The two most recent human deaths from canine rabies contracted within the U.S., for instance, were a seven-year-old girl, bitten by a rabid dog in Texas in June 1979, and a 13-year-old boy who was bitten by a rabid dog in Kansas in 1968.
The subsequent introduction of oral rabies vaccines enabled some nations without significant reservoirs of bat rabies to eradicate rabies altogether.
There is as yet no effective method of vaccinating bats, although in theory it could be done with aerosolized vaccines that could be sprayed into caves, hollow tree trunks, attics, and other relatively inaccessible bat habitats.
Success in Europe & the U.S.
Recounted Debora MacKenzie for New Scientist in 2005, “Switzerland became rabies-free in 1998, thanks to a huge campaign in which biscuits doped with vaccine were distributed in fox habitats. France was next to eliminate the disease, in 2000, followed by Belgium and Luxembourg in 2001. In 2000, this helped convince the rabies-free United Kingdom to end compulsory quarantine for mammals brought in from some European countries.”
The U.S. had since 1976 fought a losing battle against raccoon rabies in the mid-Atlantic states, southern New England, upstate New York, and as far west as Ohio.
Begun when raccoon hunters and trappers tried to rebuild the hunted and trapped out raccoon population of the Great Smokies National Park region with raccoons translocated from Florida, some of them already rabid, the mid-Atlantic raccoon rabies pandemic radiated outward at the rate of about 50 miles per year.
Finally, in 1994, the late Tufts School of Veterinary Medicine president Franklin Loew (1940-2003) began demonstrating the efficacy of an oral rabies vaccine developed by Charles Rupprecht at the Wistar Institute in Philadelphia.
Raccoons, foxes, & coyotes
The Rupprecht-designed capsules were a sort of fish meal sandwich, containing a vaccine dose in a wax capsule, genetically engineered to be released and absorbed only by stomach enzymes unique raccoons.
Stopping the raccoon rabies pandemic cold within the next few years, the same technology was adapted to stop a fox rabies outbreak that threatened to spread south from Quebec and Ontario.
Oral rabies vaccination may have been most spectacularly successful in Texas, however, where mid-winter air drops of canine rabies vaccine pellets began in 1996 not only quelled a rare rabies outbreak among coyotes, but achieved a 98% reduction of canine rabies in all species by 1998.
Eradicating canine rabies worldwide through the use of oral rabies vaccine pellets engineered specifically for dogs appeared to be an attainable goal––except that in warmer climates, any rabies vaccines rapidly became ineffective, regardless of how they were administered.
What are “Immunogenicity” & “seroconversion”?
Summarized Shimshony, translation below, “The studies [done in Namibia] addressed the immunogenicity of the highly attenuated third generation oral rabies vaccine strain SPBN GASGAS in local free-roaming dogs, assessed by determining the immune response in terms of seroconversion for up to 56 days post-vaccination.
In translation, the Namibian scientists investigated the ability of their oral rabies vaccination to provoke an immune response in street dogs. This was done by measuring the “seroconversion rate.”
“Seroconversion” is defined as “the transition from the point of viral infection to when antibodies against the virus become present in the blood.”
Dogs who consumed the oral rabies vaccination baits were found to be immune to rabies 56 days afterward. Further testing will be needed to confirm the effectiveness of the vaccine over longer intervals, but usually a vaccine that is effective over eight weeks will remain effective for a year or more.
The science explained
“At two study sites,” Shimshony wrote, “free-roaming dogs were vaccinated by administering the vaccine either by direct oral administration or via a vaccine-loaded egg bait. Pre- and post-vaccination blood samples were tested for rabies virus neutralizing, as well as binding antibodies using standard serological assays.”
In the Namibian field trial, Shimshony reported, “About 78% of the dogs vaccinated by the oral route seroconverted, though the seroconversion as determined by a rapid fluorescence focus inhibition test was much lower.”
Translation: tissue samples were examined under a fluoroscope, defined as “an instrument consisting of a surface containing chemicals called phosphors that glow when struck by X rays or gamma rays.”
A fluoroscope is “used to transform images made up of invisible radiations into visible light.”
The presence of rabies in an animal is most easily and accurately confirmed by using microscopic fluoroscopy of a tissue sample to detect and count “Negri bodies.”
Negri bodies, named after the Italian pathologist Adelchi Negri (1876-1912) are biological “cinders” produced by rabies infection.
So what is SPBN GASGAS?
The Namibian scientists concluded, “This study confirms the immunogenicity of the vaccine strain,” called SPBN GASGAS, “and the potential utility of oral rabies vaccination for the control of dog-mediated rabies in African dogs.”
SPBN GASGAS has previously been used in oral rabies vaccines for dogs, cats, red foxes, raccoons, mongooses, striped skunks, domestic pigs, and tanuki (raccoon dogs).
Finished Shimshony, “It will be helpful to obtain information on the shape and size of the vaccine-loaded egg baits applied for the oral vaccination of the inaccessible dogs.”
The beginning of the end of canine rabies?
The goal of the Namibian Ministry of Agriculture, Water & Land Reform is to eliminate human deaths from dog-mediated rabies by 2030.
As significant an accomplishment as that would be, the introduction of an oral rabies vaccine that remains effective in southern hemisphere climates could be the beginning of canine rabies eradication throughout the last remaining canine rabies reservoirs in the rest of the southern hemisphere as well.
As well as Africa, targeted regions would include Indian subcontinent, Southeast Asia, and parts of South America.
Conventional vaccination works well if anyone can catch the dogs
Conventional injectable rabies vaccination campaigns directed by Oscar Larghi, M.D., beginning in 1985, Larghi reported to the Program for Monitoring Emerging Diseases in May 1998, “with little emphasis in dog population reduction (less than 10% of the estimated population), were applied in the metropolitan area of Buenos Aires, Argentina (10.5 million inhabitants), Lima-Callao, Peru (6.5 million inhabitants), and Sao Paulo, Brazil (14 million inhabitants). Dog rabies cases were reduced to zero, from close to 5,000 cases per
year in Buenos Aires, 1,000 in Lima, and 1,200 in Sao Paulo.”
But conventional injectable rabies vaccination campaigns in less developed rural and semi-rural areas with dogs less habituated to human contact have been much less successful, with capturing the dogs for vaccination proving to be the bottleneck impeding most programs.
The advent of an effective, easily distributed oral rabies vaccine that remains effective in hot climates could be an international game-changer.
Human deaths followed reported “cattle and game” outbreak
The Namibian rabies eradication campaign, of which developing the oral vaccine is a part, began after the August 2013 deaths of two people from canine rabies at the Nyangana District Hospital, near Shambungu village, about 100 miles east of Rundu, in the Kavango East region.
The human deaths came after Namibian famers “lost an estimated 1,700 cattle and game to rabies during the period 2008 to 2012,” reported Eveline De Klerk of The New Era newspaper in Windhoek in February 2013.
Noted Shimshony then, “Namibia has experienced through the years several massive outbreaks of rabies in kudu antelopes. During 2008/2009, the number of dead antelopes due to rabies was estimated to reach 20,000. Similar outbreaks were observed in earlier years, with the largest one during the years 1977-1985, when an estimated loss of 30,000 to 50,000 antelope (20% of the population) was reported, apparently involving oral spread of rabies infection between individuals.”
But what really happened?
Well, maybe, but note first of all that the 20,000 antelope said to have died from rabies in 2008/2009 would be more than 10 times the number of “cattle and game” said to have been lost to rabies during the entire 2008-2012 time frame.
Veterinarians Otto Zapke and Beate Voights in mid-May 2006 reportedly confirmed that a rare outbreak of rabies spreading from herbivore to herbivore was responsible for the deaths of “thousands” of kudu in the Omaruru region of Namibia.
The supposed 1977-1985 rabies outbreak among kudu was cited as a precedent.
But both the Zapke and Voights report and reports of the earlier rabies outbreak among kudu drew skepticism from rabies expert Henry Wilde, M.D., then director of the Queen Saovabha Memorial Hospital in Bangkok, Thailand.
“Herbivore to herbivore transmission would be unlikely,” Wilde told ANIMALS 24-7 at the time, explaining that the Namibian climate would quickly kill any live rabies virus in dripping saliva from the victim animals, just as hot climates cause rapid deterioration of rabies vaccines that are not kept refrigerated until use.
“The most likely explanation is that another epidemic disease caused most of the kudu deaths, and/or that a small undetected biting mammal is the vector for the kudu rabies cases,” Wilde said.
A team of British, Namibian, and South African researchers headed by Karen Mansfield of the World Health Organization reported in January 2006 that, “37 rabies virus isolates originating mainly from the northern and central regions of Namibia between 1980 and 2003 suggest that jackal and kudu may form part of the same epidemiological cycle of rabies,” with the jackals apparently doing the actual rabies transmission.