Horizontal disease transmission
Horizontal disease transmission refers to the spread of infections or pathogens between individuals of the same generation, distinguishing it from vertical transmission, which occurs from mother to fetus. This type of transmission can happen through direct contact, such as touching, sharing saliva, or sexual activities, as well as through indirect contact with contaminated objects or surfaces. Common illnesses transmitted this way include sexually transmitted diseases (STDs) like HIV, chlamydia, and gonorrhea, as well as respiratory infections such as influenza.
Risk factors that facilitate horizontal transmission include poor hygiene practices, inadequate sterilization, and living conditions that promote close contact among individuals. Additionally, certain insects and animals can act as vectors, spreading diseases like malaria and Lyme disease. Diagnosis typically involves laboratory testing and physical examinations, while prevention strategies emphasize the importance of proper hygiene, safe sexual practices, and vaccination where applicable. Public health efforts to control horizontal transmission are crucial, given the potential for outbreaks and significant economic impacts associated with pandemics.
Horizontal disease transmission
Definition
Horizontal disease transmission refers to the passing of a disease or pathogen from one person to another in the same generation. The disease is not passed from woman to fetus in the perinatal period; this is done through vertical disease transmission. Symptoms depend on the specific type of acquired infection. Horizontal disease transmission occurs by direct or indirect pathogenic contact.
Routes of Transmission
Horizontal transmission arises by direct contact through touching or sharing of saliva and secretions. For example, if one sexual partner has an infection, that infection may be transmitted to another partner through genital, anal, or oral contact. More than twenty-five sexually transmitted diseases (STDs) exist, including human immunodeficiency virus (HIV) infection, chlamydia, gonorrhea, and herpes. The respiratory route is another common pathway for direct contact, whereby an infected person coughs or sneezes droplets onto a susceptible person. The pathogen enters the body through the nose, mouth, or eye and causes infections such as influenza, chickenpox, and strep throat.
Indirect transmission occurs when a person has contact with an object (fomite) or host that carries the pathogen, allowing transmission without physical contact. Infections that are spread by contact with inanimate contaminated objects are warts, syphilis, and impetigo. Risk factors include improper handwashing technique, inadequate sterilization of objects, and living in close quarters, especially under unsanitary conditions. Indirect contact with insects or animals acting as disease vectors will also lead to horizontal disease transmission. Mosquitoes transfer malaria and ticks transfer Lyme disease to humans.
Testing and Prevention
Laboratory blood work or a physical exam, or both, will diagnose a horizontally transmitted disease. Antibiotics, antiviral medications, and vaccinations are available for some infections. In the case of STDs, precautions such as abstinence or condom use help prevent future horizontal transmission. One should also clean soiled laundry and bath towels and should avoid sharing personal toiletries.
Impact
Prevention of horizontal disease transmission is of paramount importance from a public health perspective. According to the World Health Organization (WHO), there are 376 million new cases of syphilis, gonorrhea, trichomoniasis, and chlamydia among people ages 15 to 49 in one year worldwide, with HIV remaining prevalent in both developed and developing countries. If not adequately controlled, some infections can cause global pandemics, such as the H1N1 influenza outbreak. In addition, the financial impact of any pandemic is extremely high.
Bibliography
Martinson, Francis E., et al. “Risk Factors for Horizontal Transmission of Hepatitis B Virus in a Rural District in Ghana.” American Journal of Epidemiology 147 (1997): 478-487.
"More Than 1 Million New Curable Sexually Transmitted Infections Every Day." World Health Organization (WHO), 6 June 2019, www.who.int/news/item/06-06-2019-more-than-1-million-new-curable-sexually-transmitted-infections-every-day. Accessed 4 Feb. 2025.
Ogata, Shohei, et al. "Investigation of Vertical and Horizontal Transmission of Spiroplasma in Ticks under Laboratory Conditions." Scientific Reports, vol. 13, no. 13265, 15 Aug. 2023, doi.org/10.1038/s41598-023-39128-z. Accessed 4 Feb. 2025.
Okinyi, M., et al. “Horizontally-Acquired HIV Infection in Kenyan and Swazi Children.” International Journal of STD and AIDS Online 20 (2009): 852-857.
Wilkinson, D., and G. Rutherford. “Population-Based Interventions for Reducing Sexually Transmitted Infections, Including HIV Infection.” Cochrane Database of Systematic Reviews (2001): CD001220. Available through EBSCO DynaMed Systematic Literature Surveillance at http://www.ebscohost.com/dynamed.