Mortality of captive whooping cranes caused by eastern equine encephalitis virus.

This study discusses the unexpected death of multiple whooping cranes, in a captive breeding center, due to Eastern Equine Encephalitis (EEE) infection. The research identifies symptoms, necropsy findings, the presence of EEE in various organ specimens, the spread of the disease among surviving birds, and potential mosquito vectors identified near the center.

Research Background and Procedure

• The research was conducted after observing the unusual mortality rate of the whooping cranes (39 in total) in a duration of seven weeks from September 17 to November 4, 1984, at the Patuxent Wildlife Research Center located in Laurel, Maryland.
• The researchers closely observed the symptoms and clinical signs. Before their deaths, four cranes did not show any clinical symptoms, while the remaining three showed signs of lethargy and lack of coordination (ataxia). The birds also had high levels of aspartate transaminase, gamma-glutamyl transferase, and lactic acid dehydrogenase activities, indicating possible organ damage. High uric acid concentrations were also noted, which anticipates kidney concerns.
• Following the death of the cranes, necropsies were performed to identify the cause. The birds showed symptoms of ascites (abnormal build-up of fluid in the abdomen), discoloration of the intestinal mucosa, fat depletion, enlarged liver (hepatomegaly), enlarged spleen (splenomegaly), and visceral gout. Under the microscope, significant necrosis (cell death) and inflammation were seen across various organs. Surprisingly, the Central Nervous System (CNS) was unaffected.

Research Findings and Implications

• The Eastern Equine Encephalitis (EEE) virus was isolated from the liver, kidneys, lungs, brains, and intestines of 4 out of the 7 birds that died. This led to the conclusion that EEE virus was the cause of the observed fatalities.
• In addition, EEE virus-neutralizing antibodies were found in 14 (44%) of the 32 surviving birds, confirming the spread of the EEE virus among the population.
• Interestingly, despite being in proximity with the whooping cranes, the mortality or morbidity was not detected in 240 sandhill cranes, suggesting possible species-specific susceptibility. However, 13 of the evaluated 32 sandhill cranes carried EEE virus-neutralizing antibodies.
• When testing was conducted on 41 wild birds in the area, 3 (4%) also showed presence of EEE virus-neutralizing antibodies further confirming the spread of the disease.
• Researchers found immature Culiseta melanura, mosquitos that are commonly identified as vectors (transmitters) for the EEE virus, near the research center. This points towards the potential pathway of the EEE virus transmission to the cranes.

The study suggests EEE virus is a significant threat to whooping cranes and more studies should be done regarding the susceptibility and disease progression in bird species to better understand how to protect this endangered species from such deadly outbreaks in the future.