The Numbered System: A Historical Context
Before advanced microbiology allowed for the precise identification of infectious agents, physicians often relied on clinical presentation to differentiate illnesses. The practice of numbering infectious diseases, particularly those causing a rash (exanthem), was a helpful, albeit temporary, system. This approach allowed for easier communication and classification of pediatric conditions in the late 19th and early 20th centuries. The work of Clement Dukes, who numbered the childhood exanthems, was a significant part of this medical history.
Unpacking the Second Disease: Scarlet Fever
The name 'second disease' specifically refers to scarlet fever, a bacterial infection. Unlike many of the other numbered diseases that were viral, scarlet fever is caused by toxin-producing strains of Group A Streptococcus (Streptococcus pyogenes). This is the same bacteria responsible for strep throat, but the scarlet fever rash appears due to an erythrogenic toxin produced by some strains. The disease was first described centuries ago, but its inclusion as 'second disease' solidified its place in this particular medical classification.
Key Symptoms of Scarlet Fever
Recognizing the symptoms of scarlet fever is crucial for timely treatment. These can include:
- High fever: Often the first sign, with a temperature of 101°F (38.3°C) or higher.
- Sore throat: Often severe, sometimes with white or yellow patches.
- Rash: A characteristic red, fine-textured rash that feels like sandpaper. It usually starts on the neck and chest and spreads to the trunk and extremities.
- Strawberry tongue: The tongue develops a bumpy appearance with a white or red coating.
- Pastia's lines: Redder streaks in the folds of the skin, such as the armpits and elbows.
The Cause and Modern Treatment
The bacterial cause of scarlet fever, Streptococcus pyogenes, spreads through respiratory droplets, such as from a cough or sneeze. Today, the infection is diagnosed with a rapid strep test or a throat culture. Unlike the historical era when treatment was limited, modern medicine provides a clear course of action. Antibiotics, typically penicillin or amoxicillin, are highly effective in treating scarlet fever. Prompt treatment is critical to prevent serious complications.
The Fate of the Numbered Exanthems
With advancements in microbiology, virology, and vaccine development throughout the 20th century, the numbered system became obsolete. Researchers identified the specific viral or bacterial pathogens behind these rashes, allowing for more precise diagnosis and treatment. For example, the first disease, measles, is now understood to be caused by the rubeola virus, while the third disease is caused by the rubella virus.
The fourth disease, Filatov-Dukes' disease, is perhaps the most interesting case. It was proposed as a separate entity but is now believed to be either a mild form of scarlet fever or a different staphylococcal infection, and its existence as a distinct illness is widely disputed.
Comparing the Historical Childhood Exanthems
The following table provides a quick comparison of the historical numbered diseases, which helps explain the context around the second disease.
| Disease Number | Historical Name | Modern Medical Name | Cause |
|---|---|---|---|
| First Disease | Rubeola | Measles | Measles virus |
| Second Disease | Scarlet Fever | Scarlet Fever (Scarlatina) | Streptococcus pyogenes |
| Third Disease | Rubella | German Measles | Rubella virus |
| Fourth Disease | Filatov-Dukes' disease | N/A (likely staphylococcal) | Misclassified or non-existent entity |
| Fifth Disease | Erythema Infectiosum | Parvovirus B19 | Parvovirus B19 |
| Sixth Disease | Roseola Infantum | Roseola | Human Herpesvirus 6 (HHV-6) |
Conclusion: From Number to Named
Understanding what is the second disease known as is more than just a medical trivia question; it is a lesson in medical history. The transition from a numbered classification to one based on specific pathogens reflects the monumental progress in scientific understanding. While the numerical names have faded from everyday medical practice, they remain a fascinating part of pediatrics and infectious disease history. The crucial takeaway is that modern diagnosis and treatment, particularly for bacterial infections like scarlet fever, rely on scientific precision that moves far beyond simple numerical categorization. For more detailed information on scarlet fever, you can consult sources such as LITFL's article on Second Disease.
