Salmonella Java Infections Linked to Pet Ball Pythons, 2017

In July 2017, PulseNet — the national network that compares the DNA fingerprints of foodborne bacteria — spotted a cluster of five Salmonella Paratyphi B variant L(+) tartrate+ (Java) infections with matching patterns by pulsed-field gel electrophoresis. State and local health departments' first interviews pointed to animals: all five patients reported contact with snakes. CDC and its partners opened an investigation.

How they investigated

A case was anyone from whom this strain, with the outbreak's pattern, was isolated between June 17 and July 23, 2017. Investigators then:

• asked patients a snake-specific questionnaire about the type of snake, where it was bought and what it was fed, including feeder rodents;
• sampled animals and their surroundings in patients' homes;
• traced patients' snakes back through the places they were bought, looking for a shared supplier; and
• ran whole genome sequencing on bacteria from patients, animals, homes and pet food, measuring relatedness by single nucleotide polymorphism (SNP) differences.

What they found

The patients. Five cases in four states: one each in Arizona, Oklahoma and Oregon, and two in Indiana from different households with no known link. The median age was 10 years (range under 1 to 40), and four were female. No one was hospitalized and no one died. Four of the five reported a ball python in the home.

The snakes. Pythons, their water, bedding and surroundings were sampled at homes in Arizona, Oregon and one of the Indiana homes; feeder rodents were sampled in Arizona and Indiana. Tracing found no common supplier of pythons or rodents.

No human illnesses were linked to the Mbandaka or Oranienburg finds. Separately, the U.S. Department of Agriculture's National Veterinary Services Laboratories (NVSL) had identified the Java strain in three other pythons in 2017.

The genetics. Sequencing told a more specific story than the first fingerprinting:

• Only the two Indiana patients' bacteria were closely related to each other (0–2 SNP differences); the Arizona, Oklahoma and Oregon patients' bacteria were not closely related to each other or to Indiana's.
• The Arizona python's bedding matched the Arizona patient exactly (0 SNP differences).
• The Indiana python and home samples were closely related to both Indiana patients (0–2 SNP differences).
• The three NVSL python samples were not closely related to any human, animal or environmental sample.

Whole genome sequencing comparison of isolates from people, ball pythons and their surroundings. CDC figure.

Why it matters

Ball pythons (Python regius), also called royal pythons, are native to sub-Saharan Africa. Their calm nature and small size compared with other pythons make them popular pets in the United States — but, like other reptiles, they are known to carry several kinds of Salmonella.

CDC recommends that children under 5 avoid contact with reptiles. The median patient age here was 10, a reminder that older children can get sick too.

The investigation also shows why Salmonella clusters that come from animals call for a One Health approach, with agriculture and health departments working together.

Sources

• Krishnasamy V, Stevenson L, Koski L, et al. "Notes from the Field: Investigation of an Outbreak of Salmonella Paratyphi B Variant L(+) tartrate + (Java) Associated with Ball Python Exposure — United States, 2017." Morbidity and Mortality Weekly Report 67(19), Centers for Disease Control and Prevention.
• The imported copy of the report broke off in the middle of its genetic results; that paragraph was recovered from the archived CDC page.