A cattle vaccine that makes people ill, and hides from the test

Human brucellosis is rare in the United States — 80 to 120 cases a year,
most acquired abroad — because of two things: pasteurisation, and the
State-Federal Cattle Brucellosis Eradication Program, which has
eliminated B. abortus in livestock except where wildlife reintroduce it.

The programme's tools are surveillance and vaccination. **RB51 — a live,
attenuated vaccine — has been used in US cattle since 1996.**

And that is where these cases come from.

**Although rare, it is possible for cattle to shed RB51 in their milk, even
when vaccine label recommendations are followed.**

Three confirmed cases since August 2017, each linked to **domestically
acquired raw milk products**. At least **eight people met the probable case
definition**, and **hundreds across dozens of states were potentially
exposed.**

Two reasons it goes undiagnosed

This is the part a clinician needs, because RB51 infection is not like the
brucellosis in the textbook:

A patient presents with fever, joint pain, muscle pain and sweats — which
is the nonspecific picture of half of medicine — the serology comes back
negative, and if brucellosis is treated anyway the standard regimen contains a
drug the organism shrugs off.

Hence the instruction: **when evaluating patients with symptoms consistent
with brucellosis, consider RB51 infection and ask about raw milk consumption
as part of the exposure history.** The exposure history is the diagnostic test.

The wider risk

Raw milk carries E. coli, Campylobacter, Listeria and Brucella,
and outbreaks occur more often in states where raw milk sales are legal —
which is about 75% of US states in some form.

Brucellosis in humans brings fever, arthralgia, myalgia and sweats, and
miscarriage and other sequelae can occur.

Four things that could be done

The recommendations are unusually concrete about who would have to act:

• Public health and regulatory authorities: keep supporting pasteurisation,
  and consider further restricting the sale and distribution of raw milk
• State animal health officials and the cattle industry: **evaluate whether
  the RB51 vaccine is needed** in areas where B. abortus is **not endemic in
  wildlife** — the vaccine's benefit is lowest exactly where the disease is
  gone
• Vaccine labels: add information about possible shedding in milk
• Veterinarians and dairy farmers: know that **RB51 vaccination might pose
  a risk when given to cows whose milk is intended to be drunk unpasteurised**

The shape of the problem is neat and uncomfortable: a control programme that
worked so well the disease is gone, whose remaining human cases now come from
the programme itself, reaching the few people who drink the milk raw.

Source: Centers for Disease Control and Prevention, MMWR.