Role of the raccoon in the transmission of pseudorabies: a field and laboratory investigation

Serum samples were collected from 42 raccoons trapped in a pseudorabies enzootic area of Missouri. All samples were negative for neutralizing antibodies to pseudorabies virus (PRV). Raccoons were orally exposed with one of four dose levels of PRV. The raccoons were found to be susceptible to moderately large doses of PRV tissue culture infective dose (10(4) - 10(5) TCID50). All raccoons given 10(3) TCID50 of PRV survived and did not develop clinical signs. The PRV was consistently isolated from tonsillar swabs collected from raccoons that died after exposure. The PRV was also isolated from the brain, tonsils, lungs, and salivary glands of raccoons that died. It was isolated from samples of the brain and tonsils collected from a raccoon 5 days after death. Neutralizing antibodies to PRV could not be detected in the serum of raccoons that survived PRV exposure. Tonsillar swabs and tissue samples collected from these raccoons were free of PRV. The results indicated that the raccoon may serve as a short-term reservoir for PRV, but it is unlikely to have an ipizootiologic role as a long-term, subclinical carrier of the virus.     

Transmission of transmissible mink encephalopathy to raccoons (Procyon lotor) by intracerebral inoculation.

To determine the transmissibility of transmissible mink encephalopathy (TME) agent to raccoons and to provide information about clinical course, lesions, and suitability of currently used diagnostic procedures for detection of transmissible spongiform encephalopathies (TSEs) in raccoons, 4 raccoon kits were inoculated intracerebrally with a brain suspension from mink experimentally infected with TME. One uninoculated raccoon kit served as a control. All 4 animals in the TME-inoculated group showed clinical signs of neurologic disorder and were euthanized between 21 and 23 weeks postinoculation (PI). Necropsy examinations revealed no gross lesions. Spongiform encephalopathy was observed by light microscopy, and the presence of protease-resistant prion protein (PrPres) was detected by immunohistochemistry and Western blot techniques. Scrapie-associated fibrils were observed by negative-stain electron microscopy in the brains of 3 of the 4 inoculated raccoons. These findings confirm that TME is experimentally transmissible to raccoons and that diagnostic techniques currently used for TSE in livestock detect prion protein in raccoon tissue. According to previously published data, the incubation period of sheep scrapie in raccoons is 2 years, whereas chronic wasting disease (CWD) had not shown transmission after 3 years of observation. Because incubation periods for the 3 US TSEs (scrapie, TME, and CWD) in raccoons appear to be markedly different, it may be possible to use raccoons for differentiating unknown TSE agents. Retrospective genotyping of raccoons using frozen spleens showed that the raccoon PrP gene is identical to the mink gene at codons 179 and 224. Further studies, such as the incubation periods of bovine spongiform encephalopathy and other isolates of scrapie, CWD, and TME in raccoons, are needed before the model can be further characterized for differentiation of TSE agents.     

Experimental inoculation of raccoons (Procyon lotor) with Spiroplasma mirum and transmissible mink encephalopathy (TME)

The primary objective of this study was to determine whether or not Spiroplasma mirum would be capable of producing lesions of transmissible spongiform encephalopathy (TSE) when inoculated in raccoons (Procyon lotor) and, if that was possible, to compare the clinicopathological findings with those of transmissible mink encephalopathy (TME) in the same experimental model. For this purpose, 5 groups (n = 5) of raccoon kits were inoculated intracerebrally with either S. mirum and/or TME. Two other groups (n = 5) of raccoon kits served as sham-inoculated controls. All animals inoculated with TME, either alone or in combination, showed clinical signs of neurologic disorder and were euthanized within 6 mo post-inoculation (MPI). None of the carcasses revealed gross lesions. Spongiform encephalopathy was observed by light microscopy and the presence of abnormal disease-causing prion protein (PrP(d)) was detected by immunohistochemistry (IHC) and Western blot (WB) techniques in only the raccoons administered TME. Raccoons inoculated with Spiroplasma, but not administered TME agent, were euthanized at 30 MPI. They did not show clinical neurologic signs, their brains did not have lesions of spongiform encephalopathy, and their tissues were negative for S. mirum by polymerase chain reaction (PCR) and for PrP(d) by IHC and WB techniques. The results of this study indicate that Spiroplasma mirum does not induce TSE-like disease in raccoons.     

Rabies in two privately owned domestic rabbits

Two privately owned domestic rabbits (Oryctolagus cuniculus) in Maryland were found to be infected with the raccoon variant of the rabies virus in 1998. Both rabbits had an acute onset of anorexia and paralysis or paresis of the left forelimb; 1 also developed head tremors and a head tilt. One of the rabbits became ill 25 days after being attacked by a raccoon (Procyon lotor) and was euthanatized 3 days after onset of illness. The other rabbit, which was housed in an outdoor hutch, died 4 days after onset of clinical signs; the source of infection in that rabbit remains unknown. Currently, there is not a rabies vaccine approved for use in rabbits; thus, the only way to prevent the infection in rabbits is to prevent exposure. Veterinarians in rabies-enzootic areas should be familiar with the clinical signs of rabies in rabbits and should caution rabbit owners about the need to protect their pets from contact with wildlife.     

Comparative immunogenicity and efficacy studies with oral rabies virus vaccine SAD P5/88 in raccoon dogs and red foxes.

A comparative study of immunogenicity and efficacy of the oral rabies virus vaccine SAD P5/88 in raccoon dogs and foxes was conducted. The raccoon dogs received 10(6.9) (n = 6), 10(6.3) (n = 6) or 10(5.7) FFU SAD P5/88 (n = 5) by direct oral application, and subsequently all animals seroconverted. The foxes received 10(7.2) (n = 4), 10(6.2) (n = 4), 10(5.2) (n = 4) and 10(4.2) FFU SAD P5/88 (n = 5) by the same route. On days 106 and 196 post vaccination 10 raccoon dogs and 16 foxes were challenged with a relevant street virus, respectively. All 10 raccoon dogs vaccinated with 10(6.3) (n = 5) or 10(5.7) FFU SAD P5/88 (n = 5) survived the challenge, whereas all control animals (n = 5) died of rabies. Two foxes vaccinated with 10(4.2) FFU and one fox vaccinated with 10(5.2) FFU died of rabies on day 7, 17 and 12 post infection, respectively. Also all control foxes succumbed to rabies. Our findings demonstrate that SAD P5/88 is not only an effective vaccine for oral vaccination of foxes but also for that of raccoon dogs.     

Rabies surveillance in the United States during 2004

During 2004, 49 states and Puerto Rico reported 6,836 cases of rabies in nonhuman animals and 8 cases in human beings to the CDC, representing a 4.6% decrease from the 7,170 cases in nonhuman animals and 3 cases in human beings reported in 2003. Approximately 92% of the cases were in wildlife, and 8% were in domestic animals (compared with 91% and 9%, respectively, in 2003). Relative contributions by the major animal groups were as follows: 2,564 raccoons (37.5%), 1,856 skunks (27.1%), 1,361 bats (19.9%), 389 foxes (5.7%), 281 cats (4.1%), 115 cattle (1.7%), and 94 dogs (1.4%). Compared with the numbers of reported cases in 2003, cases in 2004 decreased among all groups, except bats, cattle, human beings, and "other domestics" (1 llama). Decreases in numbers of rabid raccoons during 2004 were reported by 12 of the 20 eastern states in which raccoon rabies was enzootic. In the East, Massachusetts reported the first cases of raccoon rabies detected beyond the Cape Cod oral rabies vaccine barrier. Along the western edge of the raccoon rabies epizootic (Ohio in the north and Tennessee in the south), cases of rabies were reported from unexpected new foci beyond oral rabies vaccine zones. On a national level, the number of rabies cases in skunks during 2004 decreased by 12.1% from the number reported in 2003. Once again, Texas reported the greatest number (n = 534) of rabid skunks and the greatest overall state total of rabies cases (913). Texas reported only 1 case of rabies in a dog that was infected with the dog/coyote rabies virus variant and only 22 cases associated with theTexas gray fox rabies virus variant (compared with 61 cases in 2003). The total number of cases of rabies reported nationally in foxes and raccoons declined 14.7% and 2.7%, respectively, during 2004. The 1,361 cases of rabies reported in bats during 2004 represented a 12.3% increase over the previous year's total of 1,212 cases for this group of mammals. Cases of rabies reported in cats, dogs, horses and mules, and sheep and goats decreased 12.5%, 19.7%, 31.8%, and 16.7%, respectively, whereas cases reported in cattle increased 174%. In Puerto Rico, reported cases of rabies in mongooses decreased 4.1% and rabies in dogs (9 cases) remained unchanged from those reported in 2003. Among the 8 cases of rabies in human beings, 1 person from Oklahoma and 3 from Texas died following receipt of infected organs and tissues from an Arkansas donor. In California, a person originally from El Salvador and, in Florida, a person originally from Haiti both died of canine rabies infections acquired outside the United States. In Wisconsin, a teenager contracted rabies from a bat bite and became the first known person to survive rabies despite not having received rabies vaccine prior to symptom onset.     

An epidemic of sylvatic rabies in Finland--descriptive epidemiology and results of oral vaccination.

When rabies reappeared in Finland in April 1988, the country had been rabies free since 1959. Soon a picture of sylvatic rabies become evident, its main vector and victim being the raccoon dog (Nyctereutes procyonoides). Between 8 April 1988 and 16 February 1989, 66 virologically verified cases were recorded (48 raccoon dogs, 12 red foxes, 2 badgers, 2 cats, 1 dog and 1 dairy bull) in an area estimated at 1700 km2 in south-eastern Finland. The greatest distance between recorded cases was 67 km. A positive reaction with monoclonal antibody p-41 indicated that the virus was an arctic-type strain. A field trial on oral immunization of small predators was initiated in September 1988 using Tübingen fox baits according to the Bavarian model of bait distribution. Each bait contained 5*10(7) TCID50/ml modified live rabies virus (SAD-B19). The 6 months' surveillance indicate a seroconversion rate of 72% (N = 126) in the raccoon dog population, 67% (N = 56) in the red foxes and 13% (N = 16) in the badgers, when titers greater than or equal to 1.0 IU/ml are considered seropositive. In the whole follow-up period, no statistically significant difference could be detected between the raccoon dogs and red foxes in the rate of seroconversion or in the uptake of tetracycline from the baits. Notably high antibody levels were recorded in both raccoon dogs and red foxes within 4-5 months after vaccination. Of the seropositive animals, the proportion of animals with titers 3.0 IU/ml or greater was higher in raccoon dogs (73%) than in red foxes (51%) (x2 = 5.29, p less than 0.05). The trial shows that raccoon dogs can be immunized against rabies in the field with vaccine baits originally developed for controlling sylvatic rabies in foxes.     

Rabies surveillance in the United States during 2002

During 2002, 49 states and Puerto Rico reported 7,967 cases of rabies in nonhuman animals and 3 cases in human beings to the Centers for Disease Control and Prevention, an increase of 7.2% from the 7,436 cases in non-human animals and 1 case in a human being reported in 2001. More than 92% (7,375 cases) were in wild animals, whereas 7.4% (592) were in domestic species (compared with 93.3% in wild animals and 6.7% in domestic species in 2001). Compared with cases reported in 2001, the numbers of cases reported in 2002 increased among all major reporting groups with the exception of swine and rodents and lagomorphs. The relative contributions of the major groups of animals were as follows: raccoons (36.3%; 2,891 cases), skunks (30.5%; 2,433), bats (17.2%; 1,373), foxes (6.4%; 508), cats (3.8%; 299), dogs (1.2%; 99), and cattle (1.5%; 116). Thirteen of the 19 states in which the raccoon-associated variant of the rabies virus has been enzootic reported increases in the numbers of rabid raccoons during 2002. Among those states that have engaged in wildlife rabies control programs, Ohio reported 1 case of raccoon rabies associated with the epizootic of rabies in raccoons and 1 case in an equid that was infected with a bat variant of the rabies virus, compared with 2 cases reported in terrestrial animals during 2001. Texas reported no cases of rabies associated with the dog/coyote variant of the rabies virus (compared with 1 case in 2001) and 65 cases associated with the gray fox variant of the virus (an increase of 225% from 20 cases reported in 2001). In Massachusetts and Rhode Island, states with enzootic raccoon rabies, reports of rabid skunks again exceeded those of rabid raccoons (the sixth consecutive year, although in Rhode Island, this difference decreased to only 7 more skunks than raccoons [38/31]). Tennessee reported a single case of raccoon rabies in a pet raccoon from the central part of the state; the captive animal had been transported toTennessee from northern Georgia. Nationally, the number of rabies cases in skunks during 2002 increased by 6.6% over those reported in 2001. Texas reported the greatest number (740) of rabid skunks and the greatest overall state total of rabies cases (1,049) during 2002. The 1,373 cases of rabies reported in bats during 2002 surpassed the previous year's record (1,281 cases) as the largest number of reported cases ever recorded for this group of mammals. Cases of rabies reported in cats (299), cattle (116), and dogs (99) increased by 10.7%, 41.5%, and 11.24%, respectively, from 2001 to 2002. Rabies among sheep and goats increased 400% from 3 cases in 2001 to 15 in 2002, and cases among horses and mules increased 13.7% (51 cases in 2001 to 58 in 2002). Reported cases of rabies in mongooses in Puerto Rico decreased 4.3% from the previous year (70 cases in 2001 to 67 cases in 2002), while cases of rabies in dogs increased 77% (13 to 14). California, Tennessee, and Iowa each reported a case of rabies in a human being during 2002. All cases of rabies in humans were the result of infection with bat variants of the rabies virus.     

Rabies surveillance in the United States during 2003

During 2003, 49 states and Puerto Rico reported 7,170 cases of rabies in nonhuman animals and 3 cases in human beings to the CDC. This represents a 10% decrease from the 7,967 cases in nonhuman animals and 3 cases in human beings reported in 2002. More than 91 (n = 6,556) were in wild animals, and 8.6% (614) were in domestic species (compared with 92.5% in wild animals and 74% in domestic species in 2002). The relative contributions of the major groups of animals were as follows: 2,635 raccoons (36.7%), 2,112 skunks (29.4%), 1,212 bats (16.9%), 456 foxes (6.4%), 321 cats (4.5%), 117 dogs (1.6%), and 98 cattle (1.4%). Compared with cases reported in 2002, the number of cases reported in 2003 decreased among all reporting groups with the exception of cats, dogs, equids, and swine. Ten of the 19 states with enzootic rabies in raccoons, the District of Columbia, and New York City reported decreases in the numbers of rabid raccoons during 2003. Tennessee reported 4 cases of indigenous rabies in raccoons during 2003, becoming the 20th state where rabies in raccoons is known to be enzootic. On a national level, the number of rabies cases in skunks during 2003 decreased by 13.2% from those reported in 2002. Texas again reported the greatest number (n = 620) of rabid skunks during 2003, as well as the greatest overall state total of rabies cases (909). As in 2002, Texas did not report any cases of rabies associated with the dog/coyote variant of the rabies virus, but did report 61 cases associated with the gray fox variant of the virus (compared with 65 cases in 2002).The 1,212 cases of rabies reported in bats during 2003 represented a decline of nearly 12% from the previous year's record high of 1,373 cases for this group of mammals. Cases of rabies reported in foxes.and raccoons declined 10.2% and 8.9%, respectively, during 2003. Rabies among sheep and goats decreased from 15 cases in 2002 to 12 cases in 2003, whereas cases reported in cats, dogs, and equids increased 74%, 18.2%, and 8.6%, respectively. In Puerto Rico, reported cases of rabies in mongooses and dogs decreased 26.9% and 35.7%, respectively, from those reported in 2002. Three cases of rabies in human beings were reported in California, Virginia, and Puerto Rico during 2003. The Virginia case was the first reported occurrence of rabies in a human being infected with the raccoon rabies virus variant; however, the exposure history was unknown. The California and Puerto Rico cases were the result of infections with bat and dog/mongoose rabies virus variants, respectively, and each patient had a history of a bite.     

Second passage of sheep scrapie and transmissible mink encephalopathy (TME) agents in raccoons (Procyon lotor)

To determine the transmissibility and pathogenicity of sheep scrapie and transmissible mink encephalopathy (TME) agents derived from raccoons (first passage), raccoon kits were inoculated intracerebrally with either TME (one source) or scrapie (two sources-each in separate groups of raccoons). Two uninoculated raccoon kits served as controls. All animals in the TME-inoculated group developed clinical signs of neurologic dysfunction and were euthanatized between postinoculation month (PIM) 6 and 8. Raccoons in the two scrapie-inoculated groups manifested similar clinical signs of disease, but such signs were observed much later and the animals were euthanized between PIM 12 and 18. Necropsy revealed no gross lesions in any of the raccoons. Spongiform encephalopathy was observed by use of light microscopy, and the presence of protease-resistant prion protein (PrPres) was detected by use of immunohistochemical (IHC) and Western blot analytic techniques. Results of IHC analysis indicated a distinct pattern of anatomic distribution of PrPres in the TME- and scrapie-inoculated raccoons. These findings confirm that TME and sheep scrapie are experimentally transmissible to raccoons and that the incubation periods and IHC distribution for both agents are distinct. Therefore, it may be possible to use raccoons for differentiating unknown transmissible spongiform encephalopathy (TSE) agents. Further studies, with regard to the incubation period and the pattern of PrPres deposition by use of IHC analysis in bovine spongiform encephalopathy and for other isolates of scrapie, chronic wasting disease, and TME in raccoons are needed before the model can be further characterized for differentiation of TSE agents.     

Epizootic of rabies in raccoons in Maryland from 1981 to 1987.

The epizootic of rabies in raccoons entered Maryland in 1981 and systematically moved through the state affecting raccoons in all counties except those of the lower Eastern Shore. A precoded surveillance form was provided to all county and city health departments and data were requested for each animal head submitted for testing for the year 1985. The disease persisted and, in 1987, all counties previously reporting rabies in raccoons also had documented cases in other species. The incidence of rabies in raccoons increased in late winter and peaked in March. Most human exposures occurred during daylight hours and in private yards. Agricultural areas were similarly affected by rabid animals. Analysis of vaccination status of animals exposed to rabid animals gave estimations of statewide vaccination rates for dogs (70%) and cats (28%). The danger of rabies in cats was emphasized by the large number of animals exposed by each rabid cat. The spillover of rabies in raccoons to other species persisted in all jurisdiction through 1992, with periodic upsurges of disease at 3- to 4-year intervals as the raccoon population is replenished. Rabies was not diagnosed in any human beings.     

Safety and immunogenicity of ERA strain of rabies virus propagated in a BHK-21 cell line.

The ERA strain of rabies virus was propagated in a baby hamster kidney cell line (BHK-21/C13). The viral titer was 10(1.8) tissue culture infective doses (TCID) higher than that of commercial ERA vaccine. The ERA/BHK-21 vaccine in baits retained titers of 10(6.3) to 10(6.4), TCID when subjected to daily temperature fluctuations from 9 degrees C to 24 degrees C for 21 days. This titer, according to a dose response in laboratory foxes, was still capable of immunizing up to 100% of foxes consuming a bait. The ERA/BHK-21 vaccine, when presented in baits, produced antibodies in 80 to 100% of dogs consuming more than one bait. Duration of immunity in foxes, from feeding the ERA strain rabies virus in baits, as determined by resistance to challenge with virulent virus, was at least 48 months. The vaccine strain retained some pathogenicity for nontarget species. In tests carried out on foxes, raccoons, dogs, cats and cattle, the vaccine did not cause vaccine-induced rabies. One of 14 skunks which consumed four baits developed vaccine-induced rabies, but virus could not be isolated from the salivary glands of this animal. The vaccine, when presented in baits, caused vaccine-induced rabies in 37% of laboratory mice, 3.4% of Microtus and 2.6% of Peromyscus species. Rabies virus could not be isolated from the salivary glands of rodents with vaccine-induced rabies. It was concluded that ERA virus propagated in BHK-21/C13 cells and incorporated in an acceptable bait produced a high titer, stable, immunogenic and safe vaccine for foxes.     

Rabies surveillance in the United States during 2006

During 2006, 49 states and Puerto Rico reported 6,940 cases of rabies in animals and 3 cases in humans to the CDC, representing an 8.2% increase from the 6,417 cases in animals and 1 case in a human reported in 2005. Approximately 92% of the cases were in wildlife, and 8% were in domestic animals. Relative contributions by the major animal groups were as follows: 2,615 raccoons (37.7%), 1,692 bats (24.4%), 1,494 skunks (21.5%), 427 foxes (6.2%), 318 cats (4.6%), 82 cattle (1.2%), and 79 dogs (1.1%). Compared with numbers of reported cases in 2005, cases in 2006 increased among all groups except cattle. Increases in numbers of rabid raccoons during 2006 were reported by 11 of the 20 eastern states where raccoon rabies was enzootic, and reported cases increased by 3.2% overall, compared with 2005. On a national level, the number of rabies cases in skunks during 2006 increased by 6.1% from the number reported in 2005. Once again, Texas reported the greatest number (n = 351) of rabid skunks and the greatest overall state total of animal rabies cases (889). No cases of rabies associated with the dog/coyote rabies virus variant were reported. The last identified case of this canine rabies virus variant was identified in March 2004, along the US/Mexico border. With 2006 marking the second year of no apparent transmission of the dog/coyote variant, these findings from surveillance data support the contention that the canine rabies virus variant is no longer in circulation in the United States. Total number of cases of rabies reported nationally in foxes increased 13.6%, compared with 2005. Increases in the number of reported rabid foxes were attributable to greater numbers of foxes reported with the Arctic fox rabies virus variant in Alaska, the Texas gray fox rabies virus variant in Texas, and the raccoon rabies virus variant in Virginia. The 1,692 cases of rabies reported in bats represented a 14.5% increase, compared with numbers reported in 2005, making bats the second most reported rabid animal behind raccoons. Cases of rabies in cats, dogs, horses and mules, and sheep and goats increased 18.2%, 3.9%, 12.8%, and 22.2%, respectively, whereas cases reported in cattle decreased 11.8%. In Puerto Rico, reported cases of rabies in mongooses increased 9.2%, and rabies in domestic animals, presumably attributable to spillover infection from mongooses, increased 20%. Three cases of human rabies were reported from Texas, Indiana, and California during 2006. The cases in Indiana and Texas were attributed to bat rabies virus variants, whereas the case in California was attributed to an exposure to a dog in the Philippines.     

Rabies surveillance in the United States during 2005

During 2005, 49 states and Puerto Rico reported 6,417 cases of rabies in nonhuman animals and 1 case in a human being to the CDC, representing a 6.2% decrease from the 6,836 cases in nonhuman animals and 8 cases in human beings reported in 2004. Approximately 92% of the cases were in wildlife, and 8% were in domestic animals. Relative contributions by the major animal groups were as follows: 2,534 raccoons (39.5%), 1,478 skunks (23%), 1,408 bats (21.9%), 376 foxes (5.9%), 269 cats (4.2%), 93 cattle (1.5%), and 76 dogs (1.2%). Compared with numbers of reported cases in 2004, cases in 2005 decreased among all groups, except bats, horses, and other wild animals. Decreases in numbers of rabid raccoons during 2005 were reported by 10 of the 20 eastern states in which raccoon rabies was enzootic and decreased overall by 1.2%, compared with 2004. On a national level, the number of rabies cases in skunks during 2005 decreased 20.4% from the number reported in 2004. Once again, Texas reported the greatest number (n = 392) of rabid skunks and the greatest overall state total of rabies cases (741). Texas reported no cases of rabies associated with the dog/coyote rabies virus variant and only 8 cases associated with the Texas gray fox rabies virus variant (compared with 22 cases in 2004). The total number of cases of rabies reported nationally in foxes decreased 3.3%, compared with those reported in 2004. The 1,408 cases of rabies reported in bats represented a 3.5% increase over numbers reported in 2005. Cases of rabies in cats, dogs, cattle, and sheep and goats decreased 4.3%, 19.2%, 19.1%, and 10%, respectively, whereas cases reported in horses and mules increased 9.3%. In Puerto Rico, reported cases of rabies in mongooses increased 29.8%, and rabies in domestic animals decreased 37.5%. One case of human rabies was reported from Mississippi during 2005. This case was submitted by the state to the CDC's unexplained deaths project and diagnosed as rabies retrospectively.     

Assessing Feather Cover of Laying Hens by Infrared Thermography

Brown Leghorn hens (n = 98) were assessed for feather cover using a feather scoring (FS) scale and by infrared thermography. Mean image temperature provided a real-time assessment of feather cover that was significantly related to FS. The closest approximation to FS was achieved by considering the area of the image within specific temperature ranges. The percentage of the image area within a temperature range of 17 to 24°C was positively associated with feather cover, whereas the area within a temperature range of 28 to 31°C was negatively associated with FS and indicative of a lack of cover (bare skin). Infrared thermography provided a fast, objective, and accurate assessment of feather cover on a continuous variable.     

Estimating the incubation period of raccoon rabies: a time-space clustering approach

We used a time-space clustering approach to estimate the incubation period of raccoon rabies in the wild using data from the 1999-2001 invasion of raccoon rabies into eastern Ontario from northern New York State. The time differences and geographical distances between all possible pairs of rabies cases were computed, classified and assembled into a time-space matrix. The rows of that matrix represented differences in cases in weeks and the columns represent distances between cases in kilometers and the values in the cells of the matrix represent the counts of cases at specific time and distance intervals. There was a significant cluster of pairs 5 weeks apart with apparent harmonics at additional 5-week intervals. These results are explained by assuming the incubation period of raccoon rabies had a mode of 5 weeks. The time clusters appeared consistently at distance intervals of 5 km. We discuss the possibility that the spatial intervals were influenced by the 5 km radius of the point infection control depopulation process used in 1999 and the 10-15 km radial areas used in 2000. With the practical limits of those radii, there was an intensive effort to eliminate raccoons. Our procedure is easy to implement and provides an estimate of the shape of the distribution of incubation periods for raccoon rabies.     

Parvovirus-induced encephalitis in a juvenile raccoon

A juvenile raccoon was euthanized because of severe neurologic signs. At postmortem examination, no significant gross lesions were present. Histologic evaluation demonstrated nonsuppurative encephalitis in thalamus, brainstem, and hippocampus, cerebellar Purkinje cell loss, as well as poliomyelitis and demyelination of the spinal cord. Parvovirus antigen–specific immunohistochemistry revealed immunopositive neurons in the brainstem, cerebral cortex, and hippocampus. A few Purkinje cells were also immunopositive. DNA extracted from formalin-fixed, paraffin-embedded brain tissue (thalamus, hippocampus, cerebral cortex) yielded a positive signal using PCR targeting both feline and canine parvovirus. Sequencing analyses from a fragment of the NS1 gene and a portion of the VP2 gene confirmed the presence of DNA of a recent canine parvovirus variant (CPV-2a–like virus) in the cerebellum. Our case provides evidence that a recent canine parvovirus (CPV) strain (Carnivore protoparvovirus 1) can infect cerebral and diencephalic neurons and cause encephalitis in an otherwise healthy raccoon. Parvovirus-induced encephalitis is a differential diagnosis of rabies and canine distemper in raccoons with neurologic signs.     

Rabies surveillance in the United States during 2007

SUMMARY: During 2007, 49 states and Puerto Rico reported 7,258 cases of rabies in animals and 1 case in a human to the CDC, representing a 4.6% increase from the 6,940 cases in animals and 3 cases in humans reported in 2006. Approximately 93% of the cases were in wildlife, and 7% were in domestic animals. Relative contributions by the major animal groups were as follows: 2,659 raccoons (36.6%), 1,973 bats (27.2%), 1,478 skunks (20.4%), 489 foxes (6.7%), 274 cats (3.8%), 93 dogs (1.3%), and 57 cattle (0.8%). Compared with numbers of reported cases in 2006, cases in 2007 increased among dogs, bats, foxes, and skunks while decreases were reported among cattle, cats, and skunks. Increases in numbers of rabid raccoons during 2007 were reported by 11 of the 20 eastern states where raccoon rabies was enzootic, and reported cases increased by 1.7% overall, compared with 2006. On a national level, the number of rabies cases in skunks during 2007 decreased by 1.1% from the number reported in 2006. Texas reported the greatest number (n = 362) of rabid skunks and the greatest overall state total of animal rabies cases (969). No cases of rabies associated with the dog/coyote rabies virus variant were reported. The United States remains free of dog-to-dog transmission of canine rabies virus variants. The total number of cases of rabies reported nationally in foxes increased 14.5%, compared with 2006. Increases in the number of reported rabid foxes were attributable to greater numbers of foxes reported with the Arctic fox rabies virus variant in Alaska, the Texas gray fox rabies virus variant in Texas, and the raccoon rabies virus variant in Virginia. The 1,973 cases of rabies reported in bats represented a 16.6% increase over numbers reported in 2006. Cases of rabies in dogs and in sheep and goats increased 17.7% and 18.2%, respectively, whereas cases reported in cattle, cats, and horses and mules decreased 30.5%, 13.8%, and 20.8%, respectively. In Puerto Rico, reported cases of rabies in mongooses decreased 51.5%, and rabies in domestic animals, presumably attributable to spillover infection from mongooses, increased 25%. One human rabies case was reported from Minnesota during 2007. Although typing of the rabies virus variant in this case was not possible, an investigation of this case indicated a bat as the most likely source of exposure.     

Cerebrospinal fluid analysis of rabid and vaccinia-rabies glycoprotein recombinant, orally vaccinated raccoons (Procyon lotor)

Cerebrospinal fluid obtained from clinically normal free-ranging raccoons was analyzed and compared with CSF obtained from raccoons vaccinated orally with vaccinia-rabies glycoprotein (V-RG) recombinant virus vaccine and subsequently challenged peripherally with street rabies virus, and CSF from naive, rabies virus challenge-exposed control raccoons. Significant differences were not found in CSF of free-ranging or V-RG recombinant virus vaccine recipient raccoons, and there was no evidence of CNS invasion by V-RG virus. The CSF of naive, rabies challenge-exposed control raccoons contained high numbers of lymphocytes and monocytes, compatible with rabies virus encephalitis. Although V-RG orally vaccinated challenge-exposed raccoons were protected from lethal rabies virus infection, a mild lymphocytic pleocytosis was evident at 90 days after challenge exposure.     

Prevalence of Toxoplasma gondii infection in raccoons.

Serum samples from 427 raccoons (93 from Pennsylvania, 45 from New Jersey, 72 from South Carolina, 68 from Virginia, 30 from Iowa, and 119 from Ohio) were evaluated for Toxoplasma gondii antibodies in dilutions of 1:25, 1:50, and 1:500. The distribution of T gondii antibody titers was less than 1:25 for 212 raccoons (49.6%), 1:25 for 34 raccoons (7.9%), 1:50 for 117 raccoons (27.4%), and greater than or equal to 1:500 for 64 raccoons (14.9%). Tissue cysts were seen in the liver, and tachyzoites were in the brain of a raccoon with abnormal neurologic signs and concurrent infection with canine distemper virus. Organisms in the liver were stained with anti-T gondii serum, and the raccoon had a T gondii titer of 1:160 in the agglutination test.