Abstract

In November 2003, one female and four male Guinea baboons (Papio hamadryas papio) died over the course of 6 days at Brookfield Zoo. The animals were in good nutritional condition with no significant previous medical history. Their ages ranged from 13–23 yr and they were housed with 40 other baboons in a single species exhibit. Their habitat consisted of an island where they had access to warmed outcroppings on a gunite hill and a large heated multi-room holding building providing food, water and shelter. The animals are fed inside the shelter to allow animal care staff to observe the baboons on a daily basis. Despite having access to a heated shelter at all times, several baboons in subordinate groups spend more time outdoors due to their social grouping than other more dominant animals. The animals that died belonged to two small subgroups in this population of baboons. The female and one male made up one subgroup and three males made up another.

Animal keepers observed very brief periods of lethargy, ataxia and abnormal vocalizations prior to death in several animals. Review of the pathology reports from 1972–2002 for adult baboons (>6 yr) in this colony showed that the mean and median ages at the time of death were 16.9 yr and 17.5 yr, respectively. Four of the five dead baboons were at least 2 yr older than the historic median age of death for this species at the Brookfield Zoo. All five baboons that died had some age-related lesions at necropsy but no specific findings to confirm the cause of death. During the gross necropsy it was noted that stomach contents of four of the baboons contained orange food material, two of which had a strong citrus or alcohol-like odor. Postmortem testing ruled out alcohol intoxication from possible fermenting pumpkins and fruit offered as enrichment items. Concerns of carbon monoxide poisoning from a furnace heating the island exhibit were ruled out with postmortem hematologic carboxyhemoglobin, methemoglobin and oxygen saturation testing. Gas chromatography/mass spectroscopy for toxicologic analysis was also negative. Histologically, all five baboons had pancreatic islet amyloidosis and postmortem serum biochemical analysis on two animals revealed hyperglycemia (716 mg/dl, 484 mg/dl within 3 h postmortem) suggestive of diabetes.²

The average temperature for the month of November in 2002 was 37.3°F.⁷ All baboon deaths occurred on days where the mean temperature was below average for the month (Table 1). A mortality review of this species at Brookfield Zoo identified a previous incident of acute deaths in January 1995 during which the average temperature was 11.5°F. Interestingly, prior to both mortality events, there was a 10°F temperature drop in the average daily temperature over 2 days prior to the baboon deaths. This was the largest drop in average temperature in November 2002 and January 1995.⁷ Furthermore, solar radiation, which can provide significant warmth, was below average on the days during which baboons died in both 2003 and 1995.⁷ Animals and people can tolerate very cold weather if the change is gradual and there is sufficient time to acclimate. However, sudden decreases in temperature, even if temperatures are still above freezing, can result in hypothermia. It is because of this that hypothermia cases are particularly common during the late fall and early winter months.

Table 1. Temperature data in relationship to baboon deaths

Predisposing factors for hypothermia in humans include underlying disease, alcoholism, liver damage, gender (male>female), age and lesions limiting a person’s mobility.^3,4,6 In animals, thermoregulatory responses may be inadequate in neonates, geriatric animals, hypothyroid and anesthetized animals.^1,5 The animals in this report likely had a combination of predisposing factors that contributed to their deaths. All five of the baboons were geriatric, two may have been diabetic and it appears probable that sociologic factors may have contributed as well.

Diagnosis of hypothermia in living patients can be made through measuring core-body temperature, pathognomonic ECG abnormalities (lengthening of PR, QRS, and QT intervals) and clinical signs.^1,5 Diagnosis of hypothermia postmortem is much more difficult and is based on exclusion of other causes of death taking into account the animal's history and its environment.^3,4,6 Lack of gross necropsy, histopathologic, and toxicologic findings combined with compatible temperature and weather data lead us to believe that hypothermia was a plausible cause of death in these baboons. The management practices and exhibit of this aging baboon population are being closely evaluated in an effort to prevent similar incidents in the future.

Literature Cited

1.  Dhupa, N. 1997. Hypothermia. In: L.P. Tilley and F.W.K. Smith (eds) The 5 Minute Veterinary Consult, Canine and Feline. Williams & Wilkins, Baltimore, MD. Pp. 80–81.

2.  Hubbard, G.B. 2002. Spontaneous pancreatic islet amyloidosis in 40 baboons. J. Med. Primatol. 31:84–90.

3.  Hypothermia-related deaths—Cook County, Illinois, November 1992–March 1993. 1993. Morbidity and Mortality Weekly Report. 42(47):917–919.

4.  Hypothermia-related deaths—Georgia, January 1996–December 1997 and United States, 1979–1995. MMWR. 47(48), www.cdc.gov/mmwr/PDF/wk/mm4748.pdf.

5.  Lusk, R.H. 1989. Thermoregulation. In: S.J. Ettinger (ed.) Textbook of Veterinary Internal Medicine, Diseases of the Dog and Cat. (3rd ed.). W.B. Saunders Co., Philadelphia, PA. Pp. 23–26.

6.  Taylor, A.J. and G. McGwin. 2000. Temperature-related deaths in Alabama. S. Med. J. 93:787–792.

7.  Illinois Climate Network, Illinois State Water Survey, Department of Natural Resources. Website: www.sws.uiuc.edu/warm/desc/waci.asp#ICN (VIN editor: link could not be accessed on 02/08/21).