The Mindanao, Philippines Outbreak

The outbreak of Ebola Reston (EBO-R) in the United States of America, caused by infected monkeys in the United States, prompted the Philippine government to investigate whether the workers in the primate facilities were at risk for contracting EBO-R, and, if so, to what degree were the workers at risk. The investigative team studied 186 people, 48 who were from wildlife collection areas, and the remaining 138 were from the four primate export facilities in the area (Ferlite Farms was one of the four). Twelve of the 186 people that were tested had evidence of infection with EBO-R. 22% of the workers at Ferlite Farms were positive to IFATs (indirect fluorescent antibody test), which was much higher than at the other three primate export facilities. Out of the five employees in Ferlite Farms' animal hospital, four had positive IFATs. Workers in the hospital had more positive IFATs than the rest of the workers at Ferlite Farms.

All of the monkeys at Ferlite Farms were killed after this outbreak of Ebola Reston in 1989.

(Ferlite Farms is located in a 6.1 to 7.4-acre (2.5 to 3-hectare) area in Calamba, Laguna, Philippines, which is approximately 25 miles (40 km) south of Manila. Ferlite uses open cages as their holding facilities and they use individual cages in their quarantine facility. Supposedly, Ferlite quarantines the monkeys 30 days prior to their shipment. Until 1996, Ferlite exported 1,500 monkeys every year to the United States. The monkeys Ferlite Farms used for breeding come from Zamboanga and Iligan City.)

The Reston, Virginia Outbreak

~Hazleton Research Products' Reston Primate Quarantine Unit in Reston, Virginia

~1989

October 2, 1989, 100 cynomolgus macaques (Macaca fascicularis) from Ferlite Farms in Mindanao Island, Philippines were flown from Manila, through Amsterdam to New York. They were then transported by truck to Hazleton Research Products' Reston Primate Quarantine Unit in Reston, Virginia. October 4, 1989, the monkeys were placed in Room F of the Reston Unit. Hazleton Research Products' (HRP) Reston Unit already had about 500 cynomolgus monkeys when the shipment arrived. There had not been any African species quarantined in the Reston unit for several years, therefore it is not possible that the monkeys contracted Ebola from monkeys contaminated by a previous shipment of monkeys. Because of the 1976 Marburg incident, all primates imported into the United States must be quarantined for 30 days before they are released to insure they are not infected with any diseases.

In any transcontinental shipment of animals, a high reduction rate is to be expected due to the experience on the animal, however, this particular shipment of non human primates had a far larger number of deaths in Room F than would normally have been expected. The HRP veterinarian conducted a few necropsies of the dead monkeys from this shipment in Room F. Based on the clinical symptoms and on gross anatomy, made an initial diagnosis of simian hemorrhagic fever (SHF). SHF is a terrible disease in monkeys (it does not infect humans) and is easily transmitted. The HRP vet then sent tissue samples of the dead monkey to United States Medical Research Institute of Infectious Diseases (USAMRIID) for a conclusive diagnosis. Simian hemorrhagic fever was isolated in the tissue samples that HRP sent to USAMRIID.

Before USAMRIID finished their diagnosis, HRP made the decision to euthanize the remaining monkeys in Room F to prevent possible further spread of the virus. During the ten days after the euthanization of all the monkeys in Room F, there were sporadic deaths in the remaining monkey population at Reston. The pattern of deaths, nor the pathology in the dead monkeys, was indicative of SHF, which caused the HRP vet to become alarmed.

Meanwhile, USAMRIID was conducting additional tests on the monkey tissue cultures. From an electron micrograph of damaged tissue from one of the dead Reston monkeys, they discovered Ebola was also responsible for the deaths of the Reston monkeys. Unfortunately, the pathogen was not contained by the euthanization of the monkeys in Room F, therefore 29 additional monkeys in Room H also died. The monkeys in Room H were from a separate shipment, but from the same supplier (Ferlite Farms). They had arrived at the Reston Unit on November 8.

Were the monkeys in room H contracting the pathogen from the Reston Quarantine Unit, or were they infected with the pathogen back in the Philippines?

On November 16, the Room F monkeys were euthanized, and the Room H shipment of monkeys arrived on November 8. Both the cynomolgus monkey shipments (those in Room F and Room H) came from Ferlite Farms in the Philippines, which was experiencing a hemorrhagic disease outbreak concurrently. It is possible that the Room H monkeys were sub-clinically harboring Ebola on arrival at Reston (Ebola has an incubation period ranging from five to seven days in non human primates). However the Room H monkeys arrived at the Reston unit while the monkeys in Room F were still alive.

On November 29, 1989, the Center for Disease Control (CDC) and the Virginia Department of Health met with USAMRIID, and a plan of action was formulated to insure the safety of the community and the humane treatment of the primates at Reston. November 30th, because of the threat that Ebola might spread to the remaining animals in the quarantine unit and might infect the staff, the remaining animals (about 500) in Room H were euthanized.

On November 28, 1989, Ferlite Farms, unknowingly, sent a shipment of cynomolgus monkeys to Philadelphia that were infected with Ebola.

Six of the 178 people who had contact with the infected monkeys at the Reston Quarantine Unit had contracted the stain. None of the six, however, developed a filovirus-related illness (Ebola is a filovirus). Of the six, four (all were animal handlers at one quarantine facility) had serologic evidence of a recent infection with Ebola Reston. It is likely that one of the four infected himself when he cut his finger while performing a necropsy on an infected monkey, however the mode of transmission for the other three handlers is unknown. The remaining two people had evidence of past infection, and one of the two people is a worker at a facility that temporarily houses non human primates before delivery to US quarantine facilities (The person had regular contact with quarantined non human primates for three years), and the second person was an employee at Hazleton's Texas Primate Center.

CDC researchers conducted an additional study on the prevalence of seropositivity (showing positive to a test on blood serum for a disease) to filoviruses. They tested 550 people with varying levels of exposure to the monkeys (or monkey tissues or body fluids). They used an indirect immunofluorescence assay test (IFAT) and confirmed the results using Western blot.

Forty-two of the 550 (7.6%) people tested were positive to at least one of the filoviruses (EBO-Z, EBO-S, EBO-R, EBO-CI, Marburg). Twenty-six of 266 (9.8%) import quarantine facility staff members were seropositive; sixteen of the remaining 284 (5.6%) persons had contact with monkeys (or with monkey tissue or body fluids) outside of import quarantine facilities were also seropositive. None of the 42 who tested seropositive reported having any illness believed to be caused by a filovirus.

In order to assess the significance of the collected data, the CDC conducted a cross-sectional study on the prevalence of filovirus on serum from 449 adults in outpatient primary care facilities throughout the United States. Using the same IFAT and Western blot tests, of the 449, twelve were positive (2.7%)

The Alice, Texas Outbreak

~Hazleton's Texas Primate Center and Hazleton Research Products' Reston Unit

~1990

January 31, 1990, Ferlite Farms sent a shipment of 100 macaques to Hazleton's Texas Primate Center (TPC) in Alice, Texas. The next day, 100 monkeys from Ferlite were also sent to HRP's Reston Unit in Reston, Virginia. Within one week of after they had arrived, the monkeys at both facilities had clinical signs that were identical to the signs during the first Reston outbreak. (The two shipments of monkeys from Ferlite to Reston and Alice had no contact with each other after they left Ferlite Farms.) From February 1 through March 15, forty-six of 52 animals in one of the quarantine rooms perished, and the remaining six tested positive for filovirus. Necropsy samples taken from the TPC monkeys were sent to the Center for Disease Control (CDC) for a conclusive diagnosis. The CDC determined that the monkeys were infected with simian hemorrhagic fever and Ebola.

The cages at the Texas Primate Center were numbered horizontally and stacked in two rows. In this quarantine room at TPC, monkeys had a 40% chance of dying if they were horizontal from a neighbor who had Ebola Hemorrhagic Fever. If they were vertical from a neighbor who had EHF, they had a 26% chance of dying, "Because animals were consistently fed, handled, and treated in ascending order by cage number, these data suggest that handling procedures may be implicated in transmission" (Hendricks, KA et al. Filovirus Outbreak Among Philippine Nonhuman Primates in South Texas).

Second Texas Outbreak

~Hazleton's Texas Primate Center

~1996

In March of 1996, 100 colony raised macaques from Ferlite Farms were shipped from Manila to Houston (passing through Hong Kong and Rome). March 21, 1996, these monkeys arrived to the Texas Primate Center. On March 27, one of the monkeys from this shipment showed signs of illness. The monkey died on March 30, and necropsy of this dead monkey indicated a pneumonic process. The liver tested positive for Ebola.

April 10, a second monkey that was housed at the opposite end of the block of cages from the first case became ill. April 13, this monkey's serum tested positive for Ebola, and was euthanized. (Twenty days after the monkey arrived, and thirteen days after the incubation period was over if it had contracted Ebola from the Philippines).