Immunohistochemical detection ofC. burnetii in resected cardiac valve of a 60-year-old man with Q fever endocarditis, Cayenne, French Guiana:Monoclonal antibodies againstC. burnetii and hematoxylin were used for staining; original magnification is ×50.
The chronic form of Q fever is virtually identical toendocarditis (i.e.inflammation of the inner lining of the heart),[9] which can occur months or decades following the infection. It is usually fatal if untreated. However, with appropriate treatment, the mortality falls to around 10%.[citation needed]
Diagnosis is usually based onserology[11][12] (looking for anantibody response) rather than looking for the organism itself. Serology allows the detection of chronic infection by the appearance of high levels of the antibody against the virulent form of the bacterium. Molecular detection of bacterial DNA is increasingly used. Contrary to mostobligate intracellular parasites,Coxiella burnetii can be grown in anaxenic culture, but its culture is technically difficult and not routinely available in most microbiology laboratories.[13]
Protection is offered by Q-Vax, a whole-cell, inactivated vaccine developed by an Australian vaccine manufacturing company,CSL Limited.[16] The intradermal vaccination is composed of killedC. burnetii organisms. Skin and blood tests should be done before vaccination to identify pre-existing immunity because vaccinating people who already have immunity can result in a severe local reaction. After a single dose of vaccine, protective immunity lasts for many years. Revaccination is not generally required. Annual screening is typically recommended.[17]
In 2001, Australia introduced a national Q fever vaccination program for people working in "at-risk" occupations. Vaccinated or previously exposed people may have their status recorded on the Australian Q Fever Register,[18] which may be a condition of employment in the meat processing industry or inveterinary research.[19] An earlier killed vaccine had been developed in the Soviet Union, but its side effects prevented its licensing abroad.[citation needed]
Preliminary results suggest vaccination of animals may be a method of control. Published trials proved that use of a registered phase vaccine (Coxevac) on infected farms is a tool of major interest to manage or prevent early or late abortion, repeat breeding,anoestrus, silent oestrus,metritis, and decreases in milk yield whenC. burnetii is the major cause of these problems.[20][21]
Q fever is primarily transmitted to humans through inhalation of aerosols contaminated with Coxiella burnetii from infected animals, notably cattle, sheep, and goats. Occupational groups such as farmers, veterinarians, and abattoir workers are at heightened risk. Preventive strategies include:[22]
Vaccination: In countries like Australia, where Q fever is endemic, vaccination programs targeting high-risk populations have been implemented. The vaccine has proven effective in reducing the incidence of the disease among these groups. CDC
Hygiene Measures: Implementing strict biosecurity and hygiene practices in livestock handling facilities can minimize environmental contamination. This includes proper disposal of animal waste and birthing products, which are known to harbor high concentrations of bacteria.
Public Awareness: Educating at-risk populations about Q fever transmission, symptoms, and preventive measures is crucial. Awareness campaigns can lead to early diagnosis and treatment, thereby reducing complications associated with the disease.
Treatment of acute Q fever withantibiotics is very effective.[7] Commonly used antibiotics includedoxycycline,tetracycline,chloramphenicol,ciprofloxacin, andofloxacin; the antimalarial drughydroxychloroquine is also used.[7] Chronic Q fever is more difficult to treat and can require up to four years of treatment with doxycycline andquinolones or doxycycline with hydroxychloroquine.[7] If a person has chronic Q fever, doxycycline and hydroxychloroquine will be prescribed for at least 18 months. Q fever in pregnancy is especially difficult to treat because doxycycline and ciprofloxacin are contraindicated in pregnancy. The preferred treatment for pregnancy and children under the age of eight isco-trimoxazole.[23][24]
Q fever is a globally distributedzoonotic disease caused by a highly sustainable and virulent bacterium. The pathogenic agent is found worldwide, except New Zealand[25] and Antarctica.[26] Understanding the transmission and risk factors of Q fever is crucial for public health due to its potential to cause widespread infection.
Recent data indicate that Q fever remains a significant public health concern worldwide. In 2019, the United States reported 178 acute Q fever cases and 34 chronic cases. Notably, in 2024, the state of Victoria, Australia, experienced a marked increase in Q fever cases, with 77 reported instances—a significant rise compared to the previous five years. This surge prompted health authorities to issue alerts emphasizing the importance of preventive measures and awareness.[27]
Transmission primarily occurs through the inhalation of contaminated dust, contact with contaminated milk, meat, or wool, and particularly birthing products.Ticks can transfer thepathogenic agent to other animals. While human-to-human transmission is rare, often associated with the transmission of birth products, sexual contact, and blood transfusion,[26] certain occupations pose higher risks for Q fever:[28]
It is important to note that anyone who has contact with animals infected with Q fever bacteria, especially people who work on farms or with animals, is at an increased risk of contracting the disease.[29] Understanding these occupational risks is crucial for public health.
Studies indicate a higher prevalence of Q fever in men than in women,[30][31] potentially linked to occupational exposure rates.[32] Other contributing risk factors include geography, age, and occupational exposure. Diagnosis relies onblood compatibility testing, with treatment varying for acute and chronic cases. Acute disease often responds todoxycycline, while chronic cases may require a combination ofdoxycycline andhydroxychloroquine.[33] It is worth noting that Q fever was officially reported in the United States as a notifiable disease in 1999 due to its potential biowarfare agent status.[34]
Q fever exhibits global epidemiological patterns, with higher incidence rates reported in certain countries. In Africa, wild animals in rainforests primarily transmit the disease, making itendemic.[26] Unique patterns are observed in Latin America, but reporting is sporadic and inconsistent between and among countries, making it difficult to track and address.[35]
Recent outbreaks in European countries, including the Netherlands and France, have been linked to urbanizedgoat farming, raising concerns about the safety of intensivelivestock farming practices and the potential risks of zoonotic diseases. Similarly, in the United States, Q fever is more common in livestock farming regions, especially in the West and the Great Plains. California, Texas, and Iowa account for almost 40% of reported cases, with a higher incidence during the spring and early summer when livestock are breeding, regardless of whether the infection is acute or chronic.[29]
These outbreaks have affected a significant number of people, with immunocompromised individuals being more severely impacted.[34] The global nature of Q fever and its association with livestock farming highlight the importance of implementing measures to prevent and control the spread of the disease, particularly in high-risk regions.
Older men in the West and Great Plains regions, involved in close contact with livestock management, are at a higher risk of contracting chronic Q fever.[32] This risk may be further increased for those with a history of cardiac problems.[32] The disease can manifest years after the initial infection, presenting symptoms such as non-specific fatigue, fever, weight loss, andendocarditis.[26][32] Additionally, certain populations are more vulnerable to Q fever, including children living in farming communities, who may experience similar symptoms as adults.[36] There have also been reported cases of Q fever among United States military service members,[37] particularly those deployed to Iraq or Afghanistan, which further highlights the importance of understanding and addressing the occupational risks associated with Q fever.[38]
Proper public health education is crucial in reducing the number of Q fever cases. Raising awareness about transmission routes, occupational risks, and preventive measures[34] can help prevent the spread of disease.[39]
Interdisciplinary collaboration between medical personnel and farmers is critical when developing strategies for control and prevention in a community.[40] Awareness campaigns should particularly target occupations that work with livestock, focusing on risk-reduction procedures such as herd monitoring, implementing sanitation practices andpersonal protective equipment, and vaccinating animals.[40] Locating livestock farms at least 500 meters away from residential areas can also help reduce animal-to-human transmission.[40]
Image A: A normalchest X-rayImage B: Q fever pneumonia
Q fever was first described in 1935 byEdward Holbrook Derrick[41] inslaughterhouse workers inBrisbane,Queensland. The "Q" stands for "query" and was applied at a time when the causative agent was unknown; it was chosen over suggestions of abattoir fever and Queensland rickettsial fever, to avoid directing negative connotations at either the cattle industry or the state of Queensland.[42]
An early mention of Q fever was important in one of the earlyDr. Kildare films (1939,Calling Dr. Kildare). Kildare's mentor Dr. Gillespie (Lionel Barrymore) tires of his protégé working fruitlessly on "exotic diagnoses" ("I think it's Q fever!") and sends him to work in a neighborhood clinic, instead.[45][46]
The United States investigated it as a potential biological warfare agent in the 1950s, with eventual standardization as agent OU. At Fort Detrick and Dugway Proving Ground, human trials were conducted onWhitecoat volunteers to determine the median infective dose (18 MICLD50/person i.h.) and course of infection. TheDeseret Test Center dispensed biological Agent OU with ships and aircraft, duringProject 112 andProject SHAD.[48] As a standardized biological, it was manufactured in large quantities atPine Bluff Arsenal, with 5,098 gallons in the arsenal in bulk at the time of demilitarization in 1970.[citation needed]
C. burnetii is currently ranked as a "category B"bioterrorism agent by theCDC.[49] It can be contagious and is very stable in aerosols in a wide range of temperatures. Q fever microorganisms may survive on surfaces for up to 60 days. It is considered a good agent in part because itsID50 (number of bacilli needed to infect 50% of individuals) is considered to be one, making it the lowest known.[50]
Q fever can affect many species of domestic and wild animals, including ruminants (cattle, sheep, goats, bison,[51] deer species[52][53]...), carnivores (dogs, cats,[54] seals[55]...), rodents,[56] reptiles and birds. However,ruminants (cattle, goats, and sheep) are the most frequently affected animals and can serve as a reservoir for the bacteria.[57]
In contrast to humans, though a respiratory and cardiac infection could be experimentally reproduced in cattle,[58] the clinical signs mainly affect the reproductive system. Q fever in ruminants is, therefore, mainly responsible for abortions, metritis, retained placenta, and infertility.
The clinical signs vary between species. In smallruminants (sheep and goats), it is dominated by abortions, premature births, stillbirths, and the birth of weak lambs or kids. One of the characteristics of abortions in goats is that they are very frequent and clustered in the first year or two after contamination of the farm. This is known as an abortion storm.[59]
In cattle, although abortions also occur, they are less frequent and more sporadic. The clinical picture is rather dominated by nonspecific signs such as placental retentions, metritis, and consequent fertility disorders.[60][61][62]
Except for New Zealand, which is currently free of Q fever, the disease is present globally. Numerous epidemiological surveys have been carried out. They have shown that about one in three cattle farms and one in four sheep or goat farms are infected,[63] but wide variations are seen between studies and countries. In China, Iran, Great Britain, Germany, Hungary, the Netherlands, Spain, the US, Belgium, Denmark, Croatia, Slovakia, the Czech Republic, Serbia, Slovenia, and Jordan, for example, more than 50% of cattle herds were infected with Q fever.[64][65][66][67][68][69][70]
Infected animals shed the bacteria by three routes - genital discharge, faeces, and milk.[71] Excretion is greatest at the time of parturition or abortion, and placentas and aborted fetuses are the main sources of bacteria, particularly in goats.
AsC. burnetii is small and resistant in the environment, it is easily airborne and can be transmitted from one farm to another, even if several kilometres away.[72]
A vaccine for cattle, goats, and sheep exists. It reduces clinical expression, such as abortions, and decreases the excretion of the bacteria by the animals, leading to control of Q fever in herds.[74]
Vaccination of herds against Q fever has been shown to reduce the risk of human infection.[75]
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