SAN ANTONIO — People who drank raw milk purchased at an Oklahoma dairy where a cow tested positive for rabies last year were screened for susceptibility—and in some cases given postexposure prophylaxis—but this did not deter most from continuing to buy raw milk, according to Kristy Bradley, D.V.M., of the Oklahoma State Department of Health.
The situation was of special concern, not only because of the large number of persons at risk for rabies exposure from the dairy, which sold an average of 300 gallons of raw milk per day, but because some of the purchasers were cancer patients.
“There was a physician in the area who told them that [raw milk] would help them counteract the effects of their chemotherapy and radiation therapy,” Dr. Bradley reported at a meeting of the Southwest Conference on Diseases in Nature Transmissible to Man.
The state health department decided to administer rabies postexposure prophylaxis (PEP) to selected persons who had consumed milk from the Swan Bros. dairy in Claremore during the time the infected cow was present, she said. However, the high cost of PEP meant that screening was necessary to identify those who in whom the milk likely had contact with the oral mucosa or in whom there was passage of the milk into the sinuses.
Also deemed at high risk were those with an anatomical defect of the sinus, pharynx, or hard/soft palate; open sores in the mouth, pharynx, or esophagus; recent oral surgery; very severe pharyngitis or tonsillitis; or immunosuppression.
An estimated 850 persons were screened via a phone bank, and PEP was given to 125 people (15%). Some persons not deemed at risk insisted on receiving PEP, whereas others who were advised to receive it chose not to—in some cases on the advice of their physician, Dr. Bradley said.
The Department of Health later administered a telephone questionnaire to those who received PEP to determine if their milk-buying habits had changed; some refused to respond, believing the questionnaire to be part of a government conspiracy, Dr. Bradley reported. Some even “thought their phones were being tapped” during the phone call, she said.
Of 93 households contacted, 72 responded to the questions. They consumed a mean of 3 gallons per week of raw milk, and 51% of respondents cited a belief that raw milk offers greater health benefits as their primary reason for buying unpasteurized milk. Such benefits cited by the respondents were an absence of the chemicals contained in homogenized milk, improved amino acid content, better intestinal absorption, and greater vitamin and mineral content.
Surprisingly, nearly 75% knew that raw milk can contain disease-causing bacteria or viruses, and 64% said they continued to buy raw milk after the rabies incident.
Oklahoma, unlike Texas, does not normally administer biologics to persons exposed to rabies, Dr. Bradley noted. However, the high-profile nature of the case and the fact that many physicians' offices would be closed for the December holidays motivated the commissioner of public health to administer PEP to at-risk persons in this case.
She added that her office also was motivated by a belief that primary care physicians were “not very well informed about rabies PEP.”
The risk of contracting rabies from cow's milk is poorly defined, Dr. Bradley said, but she observed that the mammary gland—unlike the salivary gland, through which bite-transmitted rabies is spread—is significantly distal to the brain, the source of the virus in the host. She said that transmission of the rabies virus via oral ingestion requires a much higher dose than does transmission via a bite. Moreover, oral transmission requires extended contact with the oral or nasal mucosa, the latter being the more effective transmission medium.
Although the federal government regulates interstate sales of all milk, intrastate sales are regulated by the states only, which vary in their restrictions. (See chart.)
Two prior cases were reported in the literature in 1996 and 1998, both in Massachusetts, she said at the meeting, which was held in conjunction with the International Conference on Diseases in Nature Communicable to Man. In both cases, rabies PEP was administered to all persons who had consumed the milk.
Dr. Bradley said that before the rabies case, two Campylobacter outbreaks had been linked to consumption of raw milk from the Oklahoma dairy.
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