Q fever
Q fever or query fever is a disease caused by infection with Coxiella burnetii, a bacterium that affects humans and other animals. This organism is uncommon, but may be found in cattle, sheep, goats, and other domestic mammals, including cats and dogs. The infection results from inhalation of a spore-like small-cell variant, and from contact with the milk, urine, feces, vaginal mucus, or semen of infected animals. Rarely, the disease is tick-borne. The incubation period can range from. Humans are vulnerable to Q fever, and infection can result from even a few organisms. The bacterium is an obligate intracellular pathogenic parasite.
Signs and symptoms
The incubation period is usually two to three weeks. The most common manifestation is flu-like symptoms: abrupt onset of fever usually around 40 °C/104 °F, malaise, profuse perspiration, severe headache, muscle pain, joint pain, loss of appetite, upper respiratory problems, dry cough, pleuritic pain, chills, confusion, and gastrointestinal symptoms, such as nausea, vomiting, and diarrhea. About half of infected individuals exhibit no symptoms.During its course, the disease can progress to an atypical pneumonia, which can result in a life-threatening acute respiratory distress syndrome, usually occurring during the first four to five days of infection.
Less often, Q fever causes hepatitis, which may be asymptomatic or become symptomatic with malaise, fever, liver enlargement, and pain in the right upper quadrant of the abdomen. This hepatitis often results in the elevation of transaminase values, although jaundice is uncommon. Q fever can also rarely result in retinal vasculitis.
The chronic form of Q fever is virtually identical to endocarditis, 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%.
A minority of Q fever survivors develop Q fever fatigue syndrome after acute infection, one of the more well-studied post-acute infection syndromes. Q fever fatigue syndrome is characterised by post-exertional malaise and debilitating fatigue. People with Q fever fatigue syndrome frequently meet the diagnostic criteria for myalgic encephalomyelitis/chronic fatigue syndrome. Symptoms often persist years after the initial infection.
Diagnosis
Diagnosis is usually based on serology 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 most obligate intracellular parasites, Coxiella burnetii can be grown in an axenic culture, but its culture is technically difficult and not routinely available in most microbiology laboratories.Q fever can cause infective endocarditis, which may require transoesophageal echocardiography to diagnose. Q fever hepatitis manifests as an elevation of alanine transaminase and aspartate transaminase, but a definitive diagnosis is only possible on liver biopsy, which shows the characteristic fibrin ring granulomas.
Prevention
Research done in the 1960s1970s by French Canadian-American microbiologist and virologist Paul Fiset was instrumental in the development of the first successful Q fever vaccine.Protection is offered by Q-Vax, a whole-cell, inactivated vaccine developed by an Australian vaccine manufacturing company, CSL Limited. The intradermal vaccination is composed of killed C. 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.
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, which may be a condition of employment in the meat processing industry or in veterinary research. An earlier killed vaccine had been developed in the Soviet Union, but its side effects prevented its licensing abroad.
Preliminary results suggest vaccination of animals may be a method of control. Published trials proved that use of a registered phase vaccine 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 when C. burnetii is the major cause of these problems.
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:
- 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
Epidemiology
Q fever is a globally distributed zoonotic disease caused by a highly sustainable and virulent bacterium. The pathogenic agent is found worldwide, except New Zealand and Antarctica. 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.
Transmission and occupational risks
Transmission primarily occurs through the inhalation of contaminated dust, contact with contaminated milk, meat, or wool, and particularly birthing products. Ticks can transfer the pathogenic agent to other animals. While human-to-human transmission is rare, often associated with the transmission of birth products, sexual contact, and blood transfusion, certain occupations pose higher risks for Q fever:- Veterinary personnel
- Stockyard workers
- Farmers
- Sheep shearers
- Animal transporters
- Laboratory workers handling potentially infected veterinary samples or visiting abattoirs
- People who cull and process kangaroos
- Hide workers
Prevalence and risk factors
Studies indicate a higher prevalence of Q fever in men than in women, potentially linked to occupational exposure rates. Other contributing risk factors include geography, age, and occupational exposure.Acute disease often responds to doxycycline, while chronic cases may require a combination of doxycycline and hydroxychloroquine. 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.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 it endemic. Unique patterns are observed in Latin America, but reporting is sporadic and inconsistent between and among countries, making it difficult to track and address.
Recent outbreaks in European countries, including the Netherlands and France, have been linked to urbanized goat farming, raising concerns about the safety of intensive livestock 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.
These outbreaks have affected a significant number of people, with immunocompromised individuals being more severely impacted. 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.