In February 1994, five plague infections were reported from northern Saudi Arabia. The patients were relatives, and the disease was preceded by the deaths of several camels and the distribution of meat from a sick camel. We were invited to determine the mode of transmission.
Methodology
We interviewed the living patients and reviewed the medical records. We also interviewed all 11 families who shared the camel meat. We visited all the houses of the patients and the places where they kept their animals. We compared plague illness with exposure to camel meat and other possible plague exposure. Refrigerated camel meat was sent for culture, and the area where the camels were fed was inspected for rodents and fleas.
Results
Five cases with plague, diagnosed by culture or IgM, had fever for over three days. Three patients presented with submandibular lymphadenitis and pharyngitis, one with severe abdominal pain and one with right axillary lymphadenitis. Eleven families (106 persons) had shared the camel meat. Four of 37 persons who ate camel meat developed plague, compared with 1 of 69 who did not eat camel meat (RR=7.7, p<0.05, Fisher's exact test). Among the 37, all 4 plague patients were among 6 persons who ate undercooked or raw camel liver (RR=undefined, p<0.01, Fisher's exact test). The plague patient who did not eat camel meat had slaughtered the camel and presented with a right axillary bubo. All families denied flea bites, and only one family had visited the area where the camel was kept. Evidence of Meriones lobycus infestation was found in the area where the camels were fed hay. Yersinia pestis and M. lobycus were isolated from fleas but not from the frozen camel meat. No camel liver remained for culture.
Conclusion
Undercooked or raw liver from the sick camel was the most probable source of plague in four patients. The fifth patient probably became infected through a cut while he slaughtered the camel. The fact that liver-associated cases presented with submandibular lymphadenitis also supports a foodborne hypothesis. Early diagnosis and proper control measures helped to contain the outbreak.