Have you ever wondered why Salmonella is called… well, Salmonella?
Spoiler alert: It’s not because it comes from salmon fish.
Today on Throwback Thursday, We travel back in time to meet the man it was named after - Dr. Daniel Elmer Salmon and see how a tiny germ became a household name for food poisoning worldwide.
What Is Salmonella?
Salmonella is a genus of bacteria from the family Enterobacteriaceae, boasting over 2,500 known serotypes, though only a handful usually cause disease in people and pets. It’s infamous for causing salmonellosis, a foodborne illness that affects both humans and animals. Think of it as a massive family of microscopic troublemakers: some mild-mannered, while others are downright dangerous.
Fun fact: Salmonella naturally lives in the intestinal tracts of many animals, including livestock, poultry, reptiles and amphibians - making it a silent passenger in many environments.
What is Salmonellosis?
As we discussed earlier, Salmonellosis is simply the name for the infection caused by Salmonella bacteria.
Think of it this way:
- Salmonella is the bacteria (the bug itself).
- Salmonellosis is the disease (the illness it causes).
If you’ve ever had food poisoning, there’s a good chance Salmonella was behind it. And yes, pets can get it too!
How Do Pets Get Salmonella? (Mode of Transmission)
- Fecal-oral route (the poop-mouth highway): This is the main way. Infected pets shed Salmonella in their poop, which can contaminate their food bowls, bedding, toys or even your hands if you clean up without washing properly.
- Direct contact: Handling infected animals or their environment without good hygiene (washing hands before eating or touching your face) spreads it easily.
- Eating contaminated prey: Reptiles, dogs, cats can get it when they consume infected preys - mice, rats or birds.
- Contaminated commercial diets: Raw diets carry a higher risk because they skip many bacterial-kill steps in processing. So feeding raw meat or treats without proper handling can expose pets (and you) to infection.
Incubation Period - How Fast Does It Hit?
Usually 6 to 72 hours after exposure. That’s between a few hours to 3 days before your pet starts looking sick, depending on how many bacteria were ingested and how strong their immune system is.
What Happens Inside Their Body? (Pathophysiology)
2. Survival & Attachment - How Does Salmonella Beat Stomach Acid?
- Acid Tolerance Response (ATR) - Before it even reaches the stomach, if Salmonella senses mildly acidic conditions (pH 5-6) in food, it activates special genes that prepare it to survive much harsher acid (pH 2-3) in the stomach. Imagine it putting on acid-proof armour before going into battle.
- Protective Cellular Mechanisms: It produces special proteins that protect its inner parts from acid damage, helping it stay alive long enough to reach its target - the intestines.
- High Infectious Dose (But Not Always): Usually, it takes a LOT of bacteria (100,000 to 10 million cells) to cause illness in healthy pets because stomach acid still kills many invaders. However, if a pet has reduced stomach acidity (e.g. from certain medications), even fewer bacteria can cause infection.
What Signs Might Pet Parents Notice in Salmonellosis?
If your pet is suffering from a Salmonella infection, you might observe:
- Diarrhoea - Often watery, sometimes mucus-filled or bloody.
- Vomiting - Not all pets vomit, but it’s common with gut infections.
- Fever - Your pet may feel warm to the touch, pant excessively, or seem generally unwell.
- Lethargy / Weakness - Less active, sleeping more than usual, reluctance to move.
- Loss of Appetite - Refusing food or eating far less than normal.
- Dehydration - Dry gums, sunken eyes, skin that doesn't snap back quickly when gently pinched (skin tent test).
- Abdominal Pain or Discomfort - Whining when touched on the belly, stretching into a ‘prayer position’, or appearing restless.
- In Severe Cases (especially in young, elderly, or immunocompromised pets): Collapse, difficulty breathing, weak pulse, signs of shock or sudden death (rare but serious).
Key note: If your pet shows diarrhoea, vomiting, severe tiredness or stops eating, especially after eating raw food or exposure to reptiles/birds, contact your veterinarian promptly. Salmonellosis can range from mild tummy upset to life-threatening illness.
What Happens After Infection?
Once a pet is exposed to Salmonella and starts showing signs of illness, what happens next depends on how their body handles the bacteria. Some pets may recover quickly, while others develop more serious disease and some may never even show signs at all.
That’s because Salmonella can exist in different states within pets, ranging from silent carriers to visibly sick animals, and in rare cases, causing life-threatening systemic infections.
What Are the Different States of Salmonella in Pets?
- Reptiles (turtles, snakes, lizards) - Almost all reptiles naturally carry Salmonella as part of their normal gut flora.
- Amphibians and birds - Often carry and shed Salmonella without getting sick.
- Some mammals - Dogs and cats can become carriers after exposure, but routine carriage is less common compared to reptiles and birds.
- Septicaemia (bloodstream infection)
- Joint infections (septic arthritis)
- Pneumonia
What Is the History of This Discovery?
When was Salmonella discovered?
Salmonella was first discovered in 1885 by Dr. Theobald Smith, an American microbiologist working under Dr. Daniel Elmer Salmon at the United States Department of Agriculture (USDA).
What was happening at that time?
In the late 1800s, the United States faced devastating outbreaks of hog cholera, a deadly disease causing mass mortality in pig herds. These outbreaks led to severe economic losses for farmers and the growing pork industry.
To tackle such livestock epidemics, the Bureau of Animal Industry (BAI) was established in May 1884. Dr. Daniel Salmon became its Chief and he assigned Dr. Theobald Smith the mission of identifying the causative agent of hog cholera to develop control measures or vaccines. This was part of a broader effort to improve animal health, increase agricultural productivity and protect public health.
How was Salmonella discovered?
While investigating hog cholera, Dr. Smith isolated a new bacterium from infected pigs in 1885. At that time, it was believed this bacterium caused hog cholera. However, later research revealed that hog cholera is actually caused by a virus and the bacterium isolated by Smith was a secondary invader, not the primary cause of the disease.
Why did this discovery happen then?
Several major scientific, agricultural and societal factors converged:
- Emergence of Germ Theory: The 1880s were shaped by Pasteur’s and Koch’s discoveries linking microbes to disease, transforming microbiology and veterinary medicine.
- Rise of Veterinary Public Health: Concern about livestock diseases threatening national food supplies and exports led to increased government investment in animal health research.
- Industrialisation of Agriculture: Post-Civil War America experienced rapid growth in livestock farming, making disease outbreaks a critical economic threat.
- Formalisation of the Veterinary Profession: Veterinary schools were opening and disease prevention became a national priority.
- Establishment of Federal Animal Health Programs: The creation of the BAI in 1884 aimed to combat livestock diseases, enforce quarantines and ensure meat safety.
- Global Scientific Revolution: American scientists were influenced by European pioneers like Pasteur, Koch and Lister, adopting bacteriological techniques for research and diagnostics.
Why is it called Salmonella?
Although Dr. Theobald Smith was the scientist who actually discovered and isolated the bacterium in 1885, he initially named it “Bacillus choleraesuis”, believing it caused hog cholera after isolating it from diseased pigs.
However, in 1900, Joseph Leon Lignières reclassified it under a new genus and named it Salmonella (Salmonella enterica var. Choleraesuis) in honour of Dr. Daniel Elmer Salmon, who was:
- Chief of the Bureau of Animal Industry (BAI)
- Smith’s supervisor
- A pioneer in veterinary public health and food safety
At the time, scientific naming conventions often honored the principal investigator or the head of the department, rather than the individual researcher who made the direct discovery. This reflected the hierarchical structure of research institutions in the late 19th century.
So, although Smith discovered it, Salmonella bears Salmon’s name as a nod to his leadership in veterinary science and public health advancements.
Despite this, it’s important to remember the scientist behind the discovery itself - Dr. Theobald Smith whose groundbreaking work laid the foundation for what we now know about Salmonella.
Who Was Dr. Theobald Smith?
Dr. Theobald Smith (July 31, 1859 - December 10, 1934) was a physician, microbiologist, pathologist, epidemiologist and medical researcher whose work profoundly impacted veterinary medicine, animal health and zoonotic disease research, even though he was not a veterinarian by degree.
Often hailed as “America’s First Great Medical Researcher,” he earned this reputation through his breadth of groundbreaking discoveries. Throughout his career, he received multiple honorary doctorates and medals recognizing his pioneering contributions to science.
Impact in Veterinary Medicine?
- Anaphylaxis Research: He described immune hypersensitivity reactions (anaphylaxis), shaping later understanding of allergic responses in veterinary and human medicine.
- Tuberculosis Research: He developed tuberculin purification methods, aiding diagnosis and control of bovine tuberculosis, a major zoonotic threat.
Named Legacies
Dr. Theobald Smith made several important discoveries in microbiology, immunology and veterinary science, including:
Many of Dr. Smith’s discoveries involved pathogens or immunological principles named under genus/species conventions or broader medical terms rather than personal eponyms. Despite this, his name endures in scientific literature, concepts and methods, continuing to shape veterinary and medical sciences today.
Who Was Dr. Daniel Elmer Salmon?
Dr. Daniel Elmer Salmon (July 23, 1850 - August 30, 1914), was an American veterinary surgeon, bacteriologist and public health pioneer, best known as the first recipient of a Doctor of Veterinary Medicine (DVM) degree in the United States. As Chief of the Bureau of Animal Industry (BAI), his leadership revolutionised veterinary public health, animal disease control, and food safety in the late 19th and early 20th centuries.
Although Salmonella was discovered by his subordinate, it was named in his honor, reflecting his pivotal role in advancing veterinary science and safeguarding livestock industries.
Fun Fact: His last name was Salmon, but he had nothing to do with fish diseases. Instead, he spent his life studying animal diseases and how they affected public health.
Impact in Veterinary Medicine?
Salmon’s contributions shaped modern veterinary public health:
- Eradication of Contagious Bovine Pleuropneumonia: Under his leadership, the US successfully eradicated this fatal cattle disease, proving that government-led veterinary interventions could protect national herds.
- Regulation of Meat Hygiene & Food Safety: As Chief of the BAI, he enforced meat inspection policies that safeguarded public health from zoonotic pathogens in meat products.
- Disease Surveillance & Veterinary Infrastructure: He established systematic animal disease surveillance and diagnostics laboratories, laying groundwork for today’s USDA Animal and Plant Health Inspection Service (APHIS).
- Promotion of Veterinary Research: He supported and championed research into animal disease control and vaccine development, recognising the interconnectedness of animal and human health long before ‘One Health’ became a formal concept.
Daniel Salmon’s Legacy
- First US veterinary doctorate holder
- Chief of BAI, pioneering animal disease eradication
- Instituted systematic meat inspection, improving public health
- Honored by naming of Salmonella genus, though Theobald Smith discovered it
- Advanced veterinary science as an essential pillar of food security and zoonotic disease prevention
How Was Salmonella Defined and Classified as We Know It Today?
Today, we recognise that Salmonella is a bacterium and importantly, it is not the causative agent of hog cholera (Classical Swine Fever). We know its transmission routes, preventive measures and treatment protocols. But how did this shift in understanding happen?
Enter Joseph Leon Lignières (1868-1933), a French-Argentinian microbiologist whose work between 1900-1904 transformed Salmonella classification forever.
Here’s How:
- Animal inoculation experiments showed that Salmonella choleraesuis could cause enteritis and septicemia in pigs,
- However, it failed to reproduce the symptoms of hog cholera (Classical Swine Fever).
- The discovery of filterable agents (viruses) as the true causative agents of hog cholera cemented the reclassification of Bacillus choleraesuis into Salmonella, no longer wrongly linked to CSF.
Through the 20th century, thousands of Salmonella serovars were identified and classified, leading to two major species:
- Salmonella enterica (includes most pathogenic strains affecting humans and animals)
- Salmonella bongori
Why Was Lignières’ Classification So Crucial?
- Provided a systematic taxonomic framework for this medically and veterinary-relevant group of bacteria
- Facilitated targeted research into their pathogenesis, epidemiology, food safety control, and public health impact
Why Is This Important?
From Theobald Smith, the brilliant microbiologist who first isolated Salmonella, to Daniel Salmon, the visionary veterinary leader it was named after and Joseph Leon Lignières, who created its systematic taxonomic classification - these men each left a lasting mark on veterinary science and public health.
Understanding the history behind disease discoveries like Salmonella helps us appreciate their significance and the progress they inspired.
Today, remembering Salmonella’s story reminds us why food safety, zoonotic disease prevention and strong veterinary public health systems remain essential for protecting both animals and humans alike.
Question for Readers
Beyond the Textbook
During my veterinary public health rotation, I vividly remember a day we traced an outbreak of diarrhoea in a small poultry farm. The farmer kept saying, “I thought Salmonella was from fish!”
It took a lot of gentle explanation to clarify that Salmonella bacteria have nothing to do with salmon fish, but rather with poor biosecurity and hygiene in food production.
That day cemented in me the importance of science communication. If farmers, pet owners, and the general public misunderstand simple disease facts, how can they prevent them effectively?
What Can Pet Parents Do?
- Practice Good Hygiene: Always wash your hands after handling raw meat animal waste or contaminated surfaces..
- Pet Care Hygiene: Keep pet feeding bowls, food prep areas and cages clean. Avoid letting pets roam freely on kitchen counters or dining tables.
- Safe Food Preparation: Avoid feeding raw eggs or undercooked meats to pets unless guided by a vet.
- Educate children on proper hand hygiene after playing with animals.
What Can The Vet Do?
- Diagnose and treat Salmonella infections in pets if symptomatic.
- Advise on safe food handling and feeding practices.
- Guide owners during outbreaks to reduce zoonotic spread.
- Report confirmed zoonotic Salmonella outbreaks to relevant public health authorities, especially if linked to food animals.
Treatment
Most human cases resolve without antibiotics, but severe cases need medical care. In pets, symptomatic treatment and vet guidance are essential.
Important Note: Avoid over-the-counter antibiotics for pets without veterinary confirmation, some can worsen carrier states.
Prognosis
Generally good with proper hygiene and treatment. However, immune-compromised individuals, the elderly and young children are at higher risk of severe illness.
Zoonotic Implications
Yes! Salmonella can pass between humans and animals (zoonotic). Reptiles, birds and poultry are common carriers. Following the preventive measures discussed above – like washing your hands after handling pets, cleaning their habitats safely, and practising good food hygiene - will keep you and your furry, feathery or scaly friends safe from this sneaky bacterium.
I once visited a household where a toddler developed severe diarrhoea. On investigation, their pet turtle roamed freely on kitchen counters. The family didn’t realise Salmonella bacteria were hitching a ride from the turtle’s shell to cutting boards and ultimately into everyone’s sandwiches.
Quick Quiz Time!
Answer: FALSE. It was named after Dr. Daniel Salmon, the first US veterinary degree holder.
Final Thoughts
It’s fascinating how a veterinary pioneer’s name became synonymous with one of the world’s most infamous bacteria. Salmonella isn’t from salmon, but thanks to Dr. Theobald Smith and Dr. Daniel Elmer Salmon, we know how to prevent its spread.
Stay vortexy, stay curious, stay clean, and remember, not everything named “Salmonella” comes from the sea.
Check out previous post - Adjusting Reptile Feeding During Rainy Season Temperature Drops