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Spread of rabies epidemic in China warrants need for specific vaccines
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Researchers say certain vaccines are needed to help end an epidemic of rabies in China that has spread to areas of the country where it was not previously problematic.
While human deaths from rabies have declined in China, costly outbreaks among livestock are being triggered in northwestern China by bites from stray dogs and wild foxes. These outbreaks, as well as some human cases, can be prevented by vaccines for wild animals and large livestock that are not available in the country, according to the researchers.
“In light of the history of rabies epidemics, we should clearly recognize the serious situation of animal rabies control as requiring hard and long-term work in China and not mask the truth simply because of the current decrease in human rabies cases,” they wrote in PLoS Neglected Tropical Diseases.
Geographic spread
In China, increased public awareness and the availability of post-exposure prophylaxis have led to a marked decrease in rabies fatalities from a recent peak of 3,300 in 2007 to 744 in 2015, the researchers reported.
Still, China has the second-highest number of reported cases of rabies in the world, according to WHO, and neglected control efforts have led to the expansion of the epidemic into areas such as the Ningxia Hui Autonomous Region (NHAR), where eight people died from rabid dog bites in 2013 — just 2 years after the first reported human cases in the region.
In the Inner Mongolia Autonomous Region (IMAR), cases of rabies related to foxes were once high, but have been absent since 2015 because of a precipitous decline in that population associated with the disease.
The researchers tested clinically suspicious brain tissue samples from dead animals in the two areas — 11 beef cattle samples and 10 dairy cow samples from IMAR, and 15 Bactrian camel samples from NHAR. All tested positive for rabies.
Further analysis showed that the dairy cows and camels were likely infected by the bites of infected dogs, while samples from beef cattle and wild foxes clustered together and were similar to isolates from countries in Eurasia.
Figure 1. A domesticated Bactrian camel in northwest China.
Source: Shou-Feng Zhang
Findings indicated that the strains of rabies associated with wild foxes that were collected in IMAR and another northwestern region, the Xinjiang Uygur Autonomous Region (XUAR), were distinct from Chinese lineages, suggesting that cross-border transmission was occurring between China and other countries such as Mongolia.
The researchers predicted that a significant increase in human and animal populations in the region means it is likely that rabies will rapidly spread among nonvaccinated animals and cross over into humans.
“Clearly, wild foxes and domestic animals should be considered for pre-exposure vaccination,” the researchers wrote, “not only to avoid financial losses or protection of wild animals, but because of their potential threat to human health.”
Vaccines needed for larger animals
As part of the study, the researchers vaccinated 300 adult cattle — 270 beef cattle and 30 dairy cows — and 330 adult camels, then randomly divided them into nine groups and immunized them with a single injection of either one, two or three doses of canine inactivated vaccine.
They analyzed blood samples from 45 randomly selected cows and 30 camels every 3 months and found that the animals that received two or three doses were still protected after 1 year.
There are enough doses of canine inactivated vaccine for domestic dogs, but oral vaccines for stray dogs and wild animals remain 5 to 10 years from approval and production in China, and no inactivated rabies vaccine for large livestock has been developed, according to the researchers.
And while a single vaccination of at least two doses of the inactivated canine vaccine was effective in cattle and camels, licensed vaccines for large domestic animals are still needed, they said.
“In conclusion, since vaccination and serological test programs for reservoir animals are the basic and effective approaches to prevent established and imported rabies in China, more research should be devoted to the development of oral vaccines for dogs and foxes,” the researchers wrote. “In addition, regular surveillance of cross-border transmission between China and neighboring countries is required for wildlife rabies control.” – by Gerard Gallagher
Disclosure: The researchers report no relevant financial disclosures.
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