Tetanus is caused by the tetanus bacterium "Clostridium tetani". Tetanus is an international health problem, as "C. tetani" spores are ubiquitous. Spores can be introduced into the body through a puncture wound (penetrating trauma). Due to "C. tetani" being an anaerobic bacterium, it and its endospores thrive in environments that lack oxygen, such as a puncture wound.

The disease occurs almost exclusively in persons inadequately immunized. It is more common in hot, damp climates with soil rich in organic matter. Manure-treated soils may contain spores, as they are widely distributed in the intestines and feces of many animals such as horses, sheep, cattle, dogs, cats, rats, guinea pigs, and chickens. In agricultural areas, a significant number of human adults may harbor the organism.

The spores can also be found on skin surfaces and in contaminated heroin. Heroin users, particularly those that inject the drug subcutaneously, appear to be at high risk of contracting tetanus. Rarely, tetanus can be contracted through surgical procedures, intramuscular injections, compound fractures, and dental infections. The bite of a dog can transmit tetanus.

Tetanus is often associated with rust, especially rusty nails. Although rust itself does not cause tetanus, objects that accumulate rust are often found outdoors or in places that harbour anaerobic bacteria. Additionally, the rough surface of rusty metal provides a habitat for "C. tetani", while a nail affords a means to puncture skin and deliver endospores deep within the body at the site of the wound. An endospore is a non-metabolizing survival structure that begins to metabolize and cause infection once in an adequate environment. Hence, stepping on a nail (rusty or not) may result in a tetanus infection, as the low-oxygen (anaerobic) environment may exist under the skin, and the puncturing object can deliver endospores to a suitable environment for growth.

Unlike many infectious diseases, recovery from naturally acquired tetanus does not usually result in immunity to tetanus. This is due to the extreme potency of the tetanospasmin toxin. Tetanospasmin will likely be lethal before it will provoke an immune response.

Tetanus can be prevented by vaccination with tetanus toxoid. The CDC recommends that adults receive a booster vaccine every ten years, and standard care practice in many places is to give the booster to any patient with a puncture wound who is uncertain of when he or she was last vaccinated, or if he or she has had fewer than three lifetime doses of the vaccine. The booster may not prevent a potentially fatal case of tetanus from the current wound, however, as it can take up to two weeks for tetanus antibodies to form.

In children under the age of seven, the tetanus vaccine is often administered as a combined vaccine, DPT/DTaP vaccine, which also includes vaccines against diphtheria and pertussis. For adults and children over seven, the Td vaccine (tetanus and diphtheria) or Tdap (tetanus, diphtheria, and acellular pertussis) is commonly used.

The World Health Organization certifies countries as having eliminated maternal or neonatal tetanus. Certification requires at least two years of rates of less than 1 case per 1000 live births. In 1998 in Uganda, 3,433 tetanus cases were recorded in newborn babies; of these, 2,403 died. After a major public health effort, Uganda in 2011 was certified as having eliminated tetanus.

The spores which cause tetanus are present everywhere, so the only prevention is immunization. Three properly spaced doses of tetanus toxoid vaccine are recommended for women of childbearing age, either before or during pregnancy; this will protect their future babies from neonatal tetanus after delivery.

In 2000 neonatal tetanus was responsible for about 14% (215,000) of all neonatal deaths. In 2008 59,000 newborns worldwide died as a result of neonatal tetanus. In 2005, 57 countries were identified as still at risk, with 27 countries accounting for 90% of cases. As of December 2013 the number of countries at risk was reduced to 25.

Human-to-human transmission of diphtheria typically occurs through the air when an infected individual coughs or sneezes. Breathing in particles released from the infected individual leads to infection Contact with any lesions on the skin can also lead to transmission of diphtheria, but this is uncommon. Indirect infections can occur, as well. If an infected individual touches a surface or object, the bacteria can be left behind and remain viable. Also, some evidence indicates diphtheria has the potential to be zoonotic, but this has yet to be confirmed. "Corynebacterium ulcerans" has been found in some animals, which would suggest zoonotic potential

Diphtheria is fatal in between 5% and 10% of cases. In children under five years and adults over 40 years, the fatality rate may be as much as 20%. In 2013, it resulted in 3,300 deaths, down from 8,000 deaths in 1990.

The number of cases has changed over the course of the last 2 decades, specifically throughout developing countries. Better standards of living, mass immunization, improved diagnosis, prompt treatment, and more effective health care have led to the decrease in cases worldwide. However, although outbreaks are rare, they still occur worldwide, especially in developed nations such as Germany among unvaccinated children, and Canada. After the breakup of the former Soviet Union in the early 1990s, vaccination rates in its constituent countries fell so low that an explosion of diphtheria cases occurred. In 1991, 2,000 cases of diphtheria occurred in the USSR. Because of this outbreak, since 1992, many of the cases reported throughout other parts of Europe have been linked to the NIS epidemic. Belgium (3/3) and Finland (10/10) come in first, stating that 100% of cases are connected to this epidemic. However, locations such as Poland and Germany have had a larger number of people diagnosed with Diphtheria overall, but claim that a smaller percentage have been linked directly to the NIS. By 1998 as many as 200,000 cases in the Commonwealth of Independent States were reported, with 5,000 deaths.

The live attenuated BCG vaccine developed against tuberculosis has been shown to have strong beneficial effects on the ability to combat non-tuberculosis infections.

Several studies have suggested that BCG vaccination may reduce atopy, particularly when given early in life. Furthermore, in multiple observational studies BCG vaccination has been shown to provide beneficial effects on overall mortality. These observations encouraged randomised controlled trials to examine BCG vaccination's beneficial non-specific effects on overall health. Since BCG vaccination is recommended to be given at birth in countries that have a high incidence of tuberculosis it would have been unethical to randomize children into 'BCG' vs. 'no BCG' groups. However, many low-income countries delay BCG vaccination for low-birth-weight (LBW) infants; this offered the opportunity to directly test the effect of BCG on overall mortality.

In the first two randomised controlled trials receipt of BCG+OPV at birth vs. OPV only ('delayed BCG') was associated with strong reductions in neonatal mortality; these effects were seen as early as 3 days after vaccination. BCG protected against sepsis as well as respiratory infections.

Among BCG vaccinated children, those who develop a BCG scar or a positive skin test (TST) are less likely to develop sepsis and exhibit an overall reduction in child mortality of around 50%.

In a recent WHO-commissioned review based on five clinical trials and nine observational studies, it was concluded that "the results indicated a beneficial effect of BCG on overall mortality in the first 6–12 months of life. Relevant follow-up in some of the trials was short, and all of the observational studies were regarded as being at risk of bias, so the confidence in the findings was rated as very low according to the GRADE criteria and "There was a suggestion that BCG vaccination may be more beneficial the earlier it is given". Furthermore, "estimated effects are in the region of a halving of mortality risk" and "any effect of BCG vaccine on all-cause mortality is not likely to be attributable to any great extent to fewer deaths from tuberculosis (i.e. to a specific effect of BCG vaccine against tuberculosis)". Based on the evidence, the WHO's Strategic Group of Experts on Immunization concluded that "the non-specific effects on all-cause mortality warrant further research".

Standard titer measles vaccine is recommended at 9 months of age in low-income countries where measles infection is endemic and often fatal. Many observational studies have shown that measles-vaccinated children have substantially lower mortality than can be explained by the prevention of measles-related deaths. Many of these observational studies were natural experiments, such as studies comparing the mortality before and after the introduction of measles vaccine and other studies where logistical factors rather than maternal choice determined whether a child was vaccinated or not.

These findings were later supported in randomized trials from 2003 to 2009 in Guinea-Bissau. An intervention group of children given standard titer measles vaccine at 4.5 and 9 month of age had a 30% reduction in all-cause mortality compared to the children in the control group, which were only vaccinated against measles at 9 month of age.

In a recent WHO-commissioned review based on four randomized trials and 18 observational studies, it was concluded that "There was consistent evidence of a beneficial effect of measles vaccine, although all observational studies were assessed as being at risk of bias and the GRADE rating was of low confidence. There was an apparent difference between the effect in girls and boys, with girls benefitting more from measles vaccination", and furthermore "estimated effects are in the region of a halving of mortality risk" and "if these effects are real then they are not fully explained by deaths that were established as due to measles". Based on the evidence, the WHO's Strategic Advisory Group of Experts on Immunization concluded that "the non-specific effects on all-cause mortality warrant further research".

In 2012, the World Health Organization estimated that vaccination prevents 2.5 million deaths each year. If there is 100% immunization, and 100% efficacy of the vaccines, one out of seven deaths among young children could be prevented, mostly in developing countries, making this an important global health issue. Four diseases were responsible for 98% of vaccine-preventable deaths: measles, "Haemophilus influenzae" serotype b, pertussis, and neonatal tetanus.

The Immunization Surveillance, Assessment and Monitoring program of the WHO monitors and assesses the safety and effectiveness of programs and vaccines at reducing illness and deaths from diseases that could be prevented by vaccines.

Vaccine-preventable deaths are usually caused by a failure to obtain the vaccine in a timely manner. This may be due to financial constraints or to lack of access to the vaccine. A vaccine that is generally recommended may be medically inappropriate for a small number of people due to severe allergies or a damaged immune system. In addition, a vaccine against a given disease may not be recommended for general use in a given country, or may be recommended only to certain populations, such as young children or older adults. Every country makes its own vaccination recommendations, based on the diseases that are common in its area and its healthcare priorities. If a vaccine-preventable disease is uncommon in a country, then residents of that country are unlikely to receive a vaccine against it. For example, residents of Canada and the United States do not routinely receive vaccines against yellow fever, which leaves them vulnerable to infection if travelling to areas where risk of yellow fever is highest (endemic or transitional regions).

A "vaccine-preventable disease" is an infectious disease for which an effective preventive vaccine exists. If a person acquires a vaccine-preventable disease and dies from it, the death is considered a vaccine-preventable death.

The most common and serious vaccine-preventable diseases tracked by the World Health Organization (WHO) are: diphtheria, "Haemophilus influenzae" serotype b infection, hepatitis B, measles, meningitis, mumps, pertussis, poliomyelitis, rubella, tetanus, tuberculosis, and yellow fever. The WHO reports licensed vaccines being available to prevent, or contribute to the prevention and control of, 25 vaccine-preventable infections.

Most strains of "H. influenzae" are opportunistic pathogens; that is, they usually live in their host without causing disease, but cause problems only when other factors (such as a viral infection, reduced immune function or chronically inflamed tissues, e.g. from allergies) create an opportunity. They infect the host by sticking to the host cell using trimeric autotransporter adhesins.

Naturally acquired disease caused by "H. influenzae" seems to occur in humans only. In infants and young children, "H. influenzae" type b (Hib) causes bacteremia, pneumonia, epiglottitis and acute bacterial meningitis. On occasion, it causes cellulitis, osteomyelitis, and infectious arthritis. It is one cause of neonatal infection.

Due to routine use of the Hib conjugate vaccine in the U.S. since 1990, the incidence of invasive Hib disease has decreased to 1.3/100,000 in children. However, Hib remains a major cause of lower respiratory tract infections in infants and children in developing countries where the vaccine is not widely used. Unencapsulated "H. influenzae" strains are unaffected by the Hib vaccine and cause ear infections (otitis media), eye infections (conjunctivitis), and sinusitis in children, and are associated with pneumonia.

Common complications include pneumonia, bronchitis, encephalopathy, earache, and seizures. Most healthy older children and adults fully recover, but those with comorbid conditions have a higher risk of morbidity and mortality.

Infection in newborns is particularly severe. Pertussis is fatal in an estimated 1.6% of hospitalized US infants under one year of age. First-year infants are also more likely to develop complications, such as: pneumonia (20%), encephalopathy (0.3%), seizures (1%), failure to thrive, and death (1%)—perhaps due to the ability of the bacterium to suppress the immune system. Pertussis can cause severe paroxysm-induced cerebral hypoxia, and 50% of infants admitted to hospital suffer apneas. Reported fatalities from pertussis in infants increased substantially from 1990 to 2010.

Infant botulism (also referred to as floppy baby syndrome) was first recognized in 1976, and is the most common form of botulism in the United States. There were 17 diagnosed cases of infant botulism in the United States in 2013. Infants are susceptible to infant botulism in the first year of life, with more than 90% of cases occurring in infants younger than six months. Infant botulism results from the ingestion of the "C. botulinum" spores, and subsequent colonization of the small intestine. The infant gut may be colonized when the composition of the intestinal microflora (normal flora) is insufficient to competitively inhibit the growth of "C. botulinum" and levels of bile acids (which normally inhibit clostridial growth) are lower than later in life.

The growth of the spores releases botulinum toxin, which is then absorbed into the bloodstream and taken throughout the body, causing paralysis by blocking the release of acetylcholine at the neuromuscular junction. Typical symptoms of infant botulism include constipation, lethargy, weakness, difficulty feeding and an altered cry, often progressing to a complete descending flaccid paralysis. Although constipation is usually the first symptom of infant botulism, it is commonly overlooked.

Honey is a known dietary reservoir of "C. botulinum" spores and has been linked to infant botulism. For this reason honey is not recommended for infants less than one year of age. Most cases of infant botulism, however, are thought to be caused by acquiring the spores from the natural environment. "Clostridium botulinum" is a ubiquitous soil-dwelling bacterium. Many infant botulism patients have been demonstrated to live near a construction site or an area of soil disturbance.

Infant botulism has been reported in 49 of 50 US states, and cases have been recognized in 26 countries on five continents.

Globally, botulism is fairly rare, with approximately 1,000 cases yearly.

The serious complications of HiB are brain damage, hearing loss, and even death.

This condition most commonly occurs after the administration of a horse origin biological agent such as equine-derived antiserum, and usually occurs 4–10 weeks after the event. Diseases that have been vaccinated against using equine-origin antiserum, resulting in subsequent Theiler's disease, include: African horse sickness, Eastern and Western Equine Encephalitis, "Bacillus anthracis", tetanus antitoxin, "Clostridium perfringens", "Clostridium botulinum", "Streptococcus equi" subspecies "equi", Equine influenza, Equine herpesvirus type 1, pregnant mare's serum, and plasma. Although it occurs sporadically, It appears to be spreadable within a premises, and there have been outbreaks occurring on farms involving multiple horses over several months. In the Northern hemisphere it is most common between August to November. It is seen almost exclusively in adult horses, and lactating broodmares given tetanus antitoxin post foaling may be more susceptible.

Worldwide, whooping cough affects around 16 million people yearly. One estimate for 2013 stated it resulted in about 61,000 deaths – down from 138,000 deaths in 1990. Another estimated 195,000 child deaths yearly from the disease worldwide. This is despite generally high coverage with the DTP and DTaP vaccines. Pertussis is one of the leading causes of vaccine-preventable deaths worldwide. About 90% of all cases occur in developing countries.

Before vaccines, an average of 178,171 cases was reported in the U.S., with peaks reported every two to five years; more than 93% of reported cases occurred in children under 10 years of age. The actual incidence was likely much higher. After vaccinations were introduced in the 1940s, pertussis incidence fell dramatically to approximately 1,000 by 1976. Incidence rates have increased since 1980. In 2015, rates in the United States were 20,762 people.

Pertussis is the only vaccine-preventable disease that is associated with increasing deaths in the U.S. The number of deaths increased from four in 1996 to 17 in 2001, almost all of which were infants under one year. In Canada, the number of pertussis infections has varied between 2,000 and 10,000 reported cases each year over the last ten years, and it is the most common vaccine-preventable illness in Toronto.

In 2009 Australia reported an average of 10,000 cases a year, and the number of cases had increased. In the U.S. pertussis in adults has increased significantly since about 2004.

This depends on the degree of hepatocellular necrosis that has occurred. Decreases in the SDH and prothrombin time along with improvement in appetite are the best positive predictive indicators of recovery. GGT may remain elevated for weeks even if the horse is recovering. Horses that survive for greater than one week and that continue to eat usually recover. Cases with rapid progression of clinical signs, uncontrollable encephalopathy, haemorrhage or haemolysis have a poor prognosis. Horses that display clinical signs have a mortality rate of 50–90%.

Prognosis is generally poor. If a patient survives, recovery may be prompt and complete, or protracted with sequelae, such as orchitis, hepatitis, uveitis, parotitis, desquamation or alopecia. Importantly, MARV is known to be able to persist in some survivors and to either reactivate and cause a secondary bout of MVD or to be transmitted via sperm, causing secondary cases of infection and disease.

Of the 252 people who contracted Marburg during the 2004–2005 outbreak of a particularly virulent serotype in Angola, 227 died, for a case fatality rate of 90%.

Although all age groups are susceptible to infection, children are rarely infected. In the 1998–2000 Congo epidemic, only 8% of the cases were children less than 5 years old.

Pregnant women with HIV may still receive the trivalent inactivated influenza vaccine and the tetanus, diphtheria, and pertussis (Tdap) vaccination during pregnancy.

Many patients who are HIV positive also have other health conditions known as comorbidities. Hepatitis B, hepatitis C, tuberculosis and injection drug use are some of the most common comorbidities associated with HIV. Women who screen positive for HIV should also be tested for these conditions so that they may be adequately treated or controlled during the pregnancy. The comorbidities may have serious adverse effects on the mother and child during pregnancy, so it is extremely important to identify them early during the pregnancy.

The disease can be prevented in horses with the use of vaccinations. These vaccinations are usually given together with vaccinations for other diseases, most commonly WEE, VEE, and tetanus. Most vaccinations for EEE consist of the killed virus. For humans there is no vaccine for EEE so prevention involves reducing the risk of exposure. Using repellent, wearing protective clothing, and reducing the amount of standing water is the best means for prevention

Women may transmit HIV to their child via breastmilk. For this reason, breastfeeding is discouraged amongst HIV-positive women. In a study conducted in South Africa, 14.1% of children born to HIV-infected mothers were infected within 6 weeks of breastfeeding and 19.5% were infected by 6 months of age. A study in Malawi found that the risk of HIV transmission through breastfeeding was 7% in children who breastfed for one year and 10% in children who breastfed for two years. The risk of HIV infection appears to be highest in the early months of breastfeeding and HIV-infected mothers should avoid breastfeeding entirely if possible.

In developed countries where clean water and infant formula are both accessible and available, HIV-positive women should not breastfeed. They should use formula to reduce the risk of transmitting HIV to the child. Even if the mother is on ART, she should avoid breastfeeding as HIV can still be transmitted through the breastmilk. Some women elect to use donor milk (breast milk donated from non-HIV infected mothers) instead of formula so that their child may receive the health benefits of breast milk, the most notable being increased immunity.

In underdeveloped countries where clean water and formula are not available, breastfeeding is encouraged to provide the child with adequate food and nutrients. The benefit of nourishment outweighs the risk of HIV transmission, malnutrition, and other infections and so breastfeeding is acceptable.

Marburgviruses are World Health Organization Risk Group 4 Pathogens, requiring Biosafety Level 4-equivalent containment, laboratory researchers have to be properly trained in BSL-4 practices and wear proper personal protective equipment.

Long term outcomes are generally good with little risk of neurological problems or epilepsy. Those who have one febrile seizure have an approximately 40% chance of having another one in the next two years, with the risk being greater in those who are younger.

Simple febrile seizures do not tend to recur frequently (children tend to outgrow them) and do not make the development of adult epilepsy significantly more likely (about 3–5%) compared with the general public (1%). Children with febrile convulsions are more likely to have a febrile seizure in the future if they were young at their first seizure (less than 18 months old), have a family history of a febrile convulsions in first-degree relatives (a parent or sibling), have a short time between the onset of fever and the seizure, had a low degree of fever before their seizure, or have a seizure history of abnormal neurological signs or developmental delay. Similarly, the prognosis after a complex febrile seizure is excellent, although an increased risk of death has been shown for complex febrile seizures, partly related to underlying conditions.

After inoculation by the vector, the virus travels via lymphatics to lymph nodes, and replicates in macrophages and neutrophils, resulting in lymphopenia, leukopenia and fever. Subsequent replication occurs in other organs leading to viremia. Symptoms in horses occur one to three weeks after infection, and begins with a fever that may reach as high as 106 °F (41 °C). The fever usually lasts for 24–48 hours.

Nervous signs appear during the fever that include sensitivity to sound, periods of excitement, and restlessness. Brain lesions appear, causing drowsiness, drooping ears, circling, aimless wandering, head pressing, inability to swallow, and abnormal gait. Paralysis follows, causing the horse to have difficulty raising its head. The horse usually suffers complete paralysis and death two to four days after symptoms appear. Mortality rates among horses with the eastern strain range from 70 to 90%.