Diseases / Miscellaneous / Multi-factorial / Metabolic Diseases / Chronic Wasting Disease of Deer and Elk / Detailed Disease Description:

< > Literature Reports of INCUBATION PERIOD for CWD of Deer and Elk:

Incubation Period

Editorial Overview (Editorial Overview Text Replicated on Overall Disease page - CWD of Deer and Elk)
  • The exact incubation period for natural CWD in cervids is not known and may vary between species. However the youngest clinically affected free-living elk (Cervus elaphus nelsoni - Rocky Mountain Elk (Cervus elaphus - Red deer)) was 21 months old, the youngest captive elk was 17 months. In Odocoileus hemionus - Mule deer the youngest naturally infected individual with clinical signs was 18 months old. In Odocoileus virginianus - White-tailed deer the youngest individual with clinical signs was 1.5 years old. Data from two outbreaks in a wildlife research facility in Colorado suggested an incubation period of 18-36 months. An incubation period of 17-24 months was seen following experimental infection by intracerebral inoculation. With experimental oral infection the incubation period was 12-34 months in elk while in mule deer the earliest onset of clinical signs occurred at 15 months after oral inoculation.
  • Experimental infection by intracerebral inoculation of infectious material into other species has produced incubation periods of six years in a goat, 22-27 months in calves of domestic cattle (Bos taurus - Domestic cattle), 17-21 months in ferrets (Mustela putorius fero - Domestic ferret (Mustela putorius - Polecat)), reduced to 8-9 months on the first serial passage and five months on the second and subsequent passages, 100-239 days in hamsters (Mesocricetus auratus - Golden Hamster (Syrian hamster)) inoculated with ferret-passaged agent, reducing to about 53-58 days on subsequent passage in hamsters, and more than 500 days in mice.

Limited data on other TSE diseases is provided in literature reports below the information on CWD. Information on these diseases within the "Chronic Wasting Disease of Deer and Elk" volume of Wildpro is provided for comparative purposes and is not intended to be comprehensive.

Source Information CWD of Deer and Elk

Cervidae:

  • Neither the minimum nor the maximum incubation period for CWD in cervids is known precisely; it is known that the youngest animal diagnosed with clinical CWD was 17 months old and the oldest was more than 15 years old. (B294.10.w10)
  • A minimum natural incubation period of 16-17 months is suggested from the fact that the youngest individual diagnosed with clinical CWD was 17 months old. (P10.67.w1)
  • The maximum incubation period for CWD is still not known. [2003] (P50.1.w7)

Cervus elaphus nelsoni - Rocky Mountain Elk (Cervus elaphus - Red deer):

  • Estimated potential range 18-36 months based on data from two outbreaks at a wildlife research facility in Colorado. (J1.34.w6)
  • The youngest recorded affected free-ranging individual was 21 months old. (J1.33.w10)
  • In elk experimentally infected orally the incubation period was approximately 12 to 34 months. (P10.67.w1)

Odocoileus hemionus - Mule deer:

  • 17 months in one of two fawns following experimental infection by intracranial inoculation of a suspension of brain tissue from an affected mule deer. (P2.31.w1)
  • 17 months and 21.5 months following experimental infection by intracranial inoculation of a suspension of brain tissue from an affected mule deer. (J64.11.w3)
  • Youngest age at which deer became clinically affected by naturally-transmitted CWD was eighteen months. (J64.11.w3)
  • 18-24 months after intracranial inoculation of fawns with brain tissue from affected deer. (J1.34.w6)
  • The earliest clinical signs were seen at sixteen months following oral inoculation of five-month-old fawns. This coincided with the earliest detection of spongiform encephalopathy in the brain. The presence of PrPres in lymphoid tissues was first detected at three months post inoculation. (P2.49.w1)
  • The presence of PrPCWD in tonsillar biopsies in naturally infected animals has been recorded in two individuals of only ten months old and in five others at 19 months old; all samples taken at three months old were negative for PrPCWD. The presence of PrPCWD in tonsillar biopsies was recorded up to 14 months prior to clinical signs and up to 20 months prior to death but may have been longer (due to the time period between samples and because adult deer may have had disease progression prior to the start of sampling).  (J223.83.w1)
  • In experimentally infected individuals the minimum incubation period from exposure to first clinical signs was about 15 months while the mean time from oral exposure to death was 23 months with a range of 20-25 months. (P10.67.w1)
  • A study of naturally-infected individuals suggested that the progression of disease may be more rapid for individuals infected early in life. (J26.39.w2)

Odocoileus virginianus - White-tailed deer:

  • The youngest individual in Wisconsin confirmed to be infected was about 5-6 months old; the youngest with clinical signs was about 1.5 years old. (V.w50)

Capra hircus - Domestic goat:

  • Approximately six years following experimental infection by intracranial inoculation of a suspension of brain tissue from an affected mule deer. (J64.11.w3)

Bos taurus - Domestic cattle:

  • Approximately 22-27 months following intracerebral inoculation of a suspension of brain tissue from affected mule deer. (J212.13.w1)

Domestic ferret Mustela putorius fero (Mustela putorius - Polecat):

  • 17-21 months following experimental infection by intracranial inoculation of a suspension of brain tissue from an affected mule deer. (P2.31.w1)
  • 17-21 months following experimental infection by intracranial inoculation of a suspension of brain tissue from an affected mule deer, reduced to 8-9 months on the first serial passage and five months on subsequent passages. (J20.251.w1)
  • 14-19 months to clinical signs and euthanasia with terminal symptoms following experimental infection by intracranial inoculation of CWD-positive deer brain. (P40.1.w23)

Mesocricetus auratus - Golden Hamster (Syrian hamster):

  • Incubation period of 132,132 and 187 days after intracerebral inoculation with second ferret-passage CWD and at 100-239 days after intracerebral inoculation with fourth ferret-passaged CWD. Inoculation using brain homogenate from a hamster which died at 132 days post inoculation resulted in an incubation period of 53 days, and passage from these hamsters resulted in clinical signs at 56 +/- 2 days.. Inoculation using brain homogenate from a hamster which died at 107 days post inoculation resulted in an incubation period of 53 days, and passage from these hamsters resulted in clinical signs at 58 +/- 4 days. (J20.251.w1)

Mus domesticus - Laboratory mouse:

  • The incubation period for CWD in experimentally infected mice was in excess of 500 days. In subsequent passages the incubation period varied depending on the PrP genotype of the mouse strain used. (J233.10.w1)
    • It was noted that the incubation period in mice infected with CWD was markedly different from any seen previously with strains of scrapie, BSE or CJD, indicating involvement of a different strain of agent. (J233.10.w1)

Other TSE Diseases

Transmissible Mink Encephalopathy

Mustela vison - American mink:

  • "An unusually long incubation period." Seven months or more; at least ten months in one case. Data from three epizootics on eight or nine mink farms in Wisconsin, USA in 1947, 1961 and 1963. (J100.115.w1)
    • In 1947 disease occurred in a group of mink which had been shipped from one farm (on which the disease later occurred) to another (on which the disease occurred only in the mink from the other, affected, farm), seven months before the outbreak occurred (shipped April 1947, disease developed late November 1947). (J100.115.w1)
    • In 1961 one of the affected farms, all of which had been using a common feed source, changed feed source seven months before the outbreak occurred. (J100.115.w1)
    • In the 1963 outbreak ten male mink which had been shipped to a new location from the main affected farm ten months previously also developed disease, while no other animals on the new premises were affected. (J100.115.w1)
  • Originally 8-12 months (from epizootiologic evidence), presumed oral exposure. On second passage, approximately eight months by oral inoculation and 6.5 months by intramuscular inoculation. Two additional passages by the intracerebral route reduced the incubation period to four months, after which it remained at this length or further passage. (J13.30.w1)
    • Variable depending on dose and route of inoculation. Incubation period was prolonged in individuals given a low dose of inoculum. Shortest, following intracerebral inoculation with high dose (dilution 10-1), 130 days, longest following intramuscular inoculation with low dose (dilution10-5), 483 days. (J13.30.w1)
  • It was noted that none of a group of 600 animals received 17th July 1984 were affected, giving an incubation period (to April1985 when the first cases occurred) of at least nine months. Since the first year breeders were affected this indicated exposure after about 1 June 1984, when mink kits started eating solid food. (J223.72.w1)
    • Following inoculation with material from infected squirrel monkeys, 4.5 months. (J223.72.w1)
    • Following intracerebral inoculation with material from infected cattle, disease after four months; following feeding of brain tissue from infected cattle disease after seven months. (J223.72.w1)
  • Data from outbreaks indicate a minimum incubation period of seven months and a maximum incubation period of 10-12 months. (J64.11.w5)

Bos taurus - Domestic cattle:

  • Following intracerebral inoculation of mink brain into two six-week-old Holstein bull calves, 18 and 19 months to sudden collapse. (J223.72.w1)
  • Following intracerebral inoculation with Hayward isolate, 455-615 days, with Blackfoot isolate 485-768 days and with cattle-passaged Stetsonville isolate 460-556 days.(J42.113.w1)

Domestic ferret Mustela putorius fero (Mustela putorius - Polecat):

  • Following intracerebral inoculation of mink brain into adults, 28-38 months. (J223.72.w1)
    • On second passage into neonatal ferrets, reduced to 8-9 months. (J223.72.w1)
  • Following inoculation into the body of ferrets one week prior to birth, no clinical signs developed at up to two years but CNS lesions were found to be present at this time; no lesions had been present in individuals examined post mortem at 59-89 days post inoculation. (J1.9.w2)

Procyon lotor - Common Raccoon:

  • Following intracerebral inoculation with Wisconsin isolate TME agent, 167, 174 and 190 days [behavioural signs may have started 2-5 weeks earlier]. Following oral inoculation with the same isolate locomotor signs were seen at 306 days, with behavioural changes starting about two weeks earlier. (J1.9.w2)

Mephitis mephitis - Striped skunk (Mustelidae - Weasels (Family)):

  • Following intracerebral inoculation with Wisconsin isolate TME agent, in one of two animals a change in personality after 4.5 months, with development of shyness. In the other animal there were no clinical signs at the time of death from unknown causes 13 months post inoculation, although there were mild histopathological lesions of spongiform encephalopathy. (J1.9.w2)

Mesocricetus auratus - Golden Hamster:

  • Following intracerebral inoculation of mink brain into weanlings, development of disease after 15-16 months. Reduced to seven months on second passage. On third passage reduced to four months with a hyperexcitable syndrome resulting or 5-7 months with a sleepy syndrome. Passage of the hyper syndrome resulted in hyper signs after only two months while passage of the sleepy syndrome resulted in hyper syndrome after two months or sleepy syndrome after 3-4 months. (J223.72.w1)

Saimiri sciurius - Squirrel monkey (Cebidae - New-world monkeys (Family)):

  • Following intracerebral inoculation of mink brain into two adults, development of disease in both animals after nine and 13 months. (J223.72.w1)
  • Following intracerebral and either intravenous or intraperitoneal inoculation of infected brain material, alteration of normal behaviour (reduced reaction to human presence after 10 months and more obvious clinical neurological signs after 11 months. (J22.169.w1)

Capra hircus - Domestic goat:

  • Following intracerebral inoculation of the Idaho strain of TME, mean 35 months (range 31-40 months). Following two passages in goats, reduction to 12-15 months. (J240.51.w1)

Ovis aries - Domestic sheep:

  • Following intracerebral inoculation of the Idaho strain of TME, mean 65 months (range 45-80 months). (J240.51.w1)

Scrapie:

  • Due to the insidious onset of clinical signs the exact incubation period is not always clear in either sheep (J35.96.w1) or goats. (J42.69.w2)
  • Assuming infection occurs around the time of birth and given the relatively short clinical course compared to the prolonged incubation period, the incubation period can be taken to be mainly two to five years, approximately the same as the age at death. (B298.10.w10)
  • Cases may occur at as young an age as 10-14 months and even seven months. (B298.10.w10)
  • Several months to several years for natural cases. (B207)
  • In experimental disease the incubation period is variable and dependant on both the strain of scrapie agent and the genetics of the recipient. (B207)
  • Natural disease in sheep in Iceland: months to years. (B292.w16)
  • Experimental disease: pooled fresh whole blood from naturally infected animals was found to transmit scrapie to healthy sheep following intravenous inoculation, with an incubation period of 21 months; in comparison intracerebral inoculation with brain material or cerebrospinal fluid gave incubation periods averaging 11.5 and 13 months respectively. (B292.w16)

Callithrix jacchus - Common marmoset (Callithrichidae - Marmosets and Tamarins (Family)):

  • Following experimental infection by intracerebral and intraperitoneal inoculation with a brain homogenate from a sheep with scrapie the incubation periods recorded were 38 and 42 months. (J3.132.w3)

Mustela vison - American mink:

  • Following experimental intracerebral infection, incubation period of 12-14 months in 5/5 mink inoculated with brain material from a scrapie-affected Suffolk sheep, but no disease during 20 months of observation in 5/5 mink inoculated with brain material from a scrapie-affected Cheviot sheep. (J22.172.w1)

Cervus elaphus nelsoni - Rocky Mountain Elk (Cervus elaphus - Red deer):

  • Following experimental infection by intracerebral inoculation of elk calves with scrapie brain, incubation periods of 25 and 35 months in two of six inoculated animals. (J26.40.w1)

Bovine Spongiform Encephalopathy (BSE):

  • Based on the ages at death of individuals thought to have been infected by ingestion of the BSE agent, the incubation period in felids appears to be longer than that in bovids. (B23.101.w4, J3.135.w1)
Acinonyx jubatus - Cheetah (Felidae - Cats (Family))
  • Incubation period of 4.5 to eight years recorded. (J2.26.w2)

Bos taurus - Domestic cattle:

  • Range 2.5 to eight years or longer, with a log normal distribution [based on computer simulation using data from epidemiological studies]. (J3.123.w2)
  • Long, 2.5 to eight years or more; youngest age at onset recorded as 22 months. (B207)
  • Following intracerebral and intravenous inoculation of cattle with homogenate from infected cattle brain, 500-650 days. (J64.11.w6)

Callithrix jacchus - Common marmoset (Callithrichidae - Marmosets and Tamarins (Family)):

  • Following experimental infection by intracerebral and intraperitoneal inoculation with a brain homogenate from a cow with BSE the incubation periods recorded were 46 and 47 months. (J3.132.w3)

Felis catus - Domestic cat:

  • "Age-specific incidences were consistent with an incubation period similar to that for BSE of approximately 60 months." (W244.09Apr2002.CWD1)

Macaca fascicularis - Cynomolgus macaques (Cercopithecidae - Old-world monkeys (Family)):

  • Following experimental infection by intracerebral inoculation, 36-40 months; with passage by intracerebral inoculation 18-21 months and with passage by intravenous inoculation 25 months. (J135.98.w2)

Oryx leucoryx - Arabian oryx:

  • Individual imported from Zurich to Regent's Park in October 1986 (born January 1986); incubation period assumed to be less than or equal to 29 months, if acquired after arrival in the UK. (J3.135.w1)

Sus domesticus - Domestic pig:

  • Pigs experimentally inoculated with BSE simultaneously by three routes (intracranial, intravenous and intraperitoneal) developed disease following an incubation period of 69-150 weeks. (J223.84.w1)

Creutzfeldt-Jakob Disease (CJD):

  • In iatrogenic cases incubation periods have varied with the source of agent and route of entry to the central nervous system: 
    • Intracerebral inoculation via stereotactic EEG (contaminated electrodes), mean 18 months (two patients, 16 and 20 months);
    • Intracerebral inoculation via neurosurgery (contaminated instruments) 20 months (four patients, 15-28 months);
    • Transmission presumably via the optic nerve following corneal transplant, 17 months (two patients, 16 and 18 months);
    • Dura mater graft (entry from the cerebral surface), 5.5 years (25 patients, 1.5-12 years);
    • Human cadaver derived gonadotrophin (haematogenous spread) 13 years (4 patients, range 12-16 years, mean calculated from the midpoint of hormone therapy to the time of onset of symptoms);
    • Human cadaver derived growth hormone (haematogenous spread) 12 years (76 patients, range 5-30 years, mean calculated from the midpoint of hormone therapy to the time of onset of symptoms). Minimum incubation periods, calculated from the end of therapy to the start of symptoms, 5-25 years. 
    • N.B. Incubation periods for cases suggest small amounts of infectious agent and peripheral rather than CNS entry of the agent into the body.
    • (B297.8.w8)
    (B297.8.w8)
  • The incubation period in growth hormone recipients developing iatrogenic CJD was shorter in those individuals who were homozygous at codon 129. (J248.4.w1)

New variant Creutzfeldt-Jakob Disease (nvCJD):

Macaca fascicularis - Cynomolgus macaques (Cercopithecidae - Old-world monkeys (Family)):

  • Experimental infection by intracerebral inoculation 25 and 30 months (two individuals). (J135.98.w2)

Kuru:

  • Approximately 4-30 years. (B297.8.w8)
  • Minimum about four years (youngest affected individuals four years old), maximum decades. (B292.w6)
  • Minimum about 4.5 years, maximum in excess of forty years. (J246.24.w1)
    • The shortest incubation periods may represent inoculation through the conjunctiva or through breaks in the skin, rather than oral exposure. (J246.24.w1)
  • Date suggests a longer incubation period for individuals heterozygous at codon 129 compared to individuals homozygous at this codon. (J248.4.w1)

Macaca mulatta - Rhesus monkey  (Cercopithecidae - Old-world monkeys (Family)):

  • Experimental infection initial incubation eight years. (J135.98.w2)

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Authors & Referees

Authors Dr Debra Bourne MA VetMB PhD MRCVS (V.w5)
Referee Suzanne I Boardman BVMS MRCVS (V.w6)

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