Tularaemia is an infection caused by the bacterium Francisella Tularensis (FT). It is a zoonosis, meaning it can spread from animals to humans. There are 2 types of bacterium, Type A which can be fatal in humans, and Type B, which causes milder symptoms and is not fatal.
Transmission of the disease can occur in a number of ways:
From a CBRN view, Tularaemia poses a significant risk due to previous attempts having been made at using the FT bacterium as Biological weapons in aerosol form. In aerosol form it is highly contagious and requires as few as 10 organisms for human infection.
Tularaemia can present in 6 different forms depending on the route of infection:
Ulceroglandular tularaemia – Infection is usually via a scratch/bite or abrasion which causes an ulcerated skin lesion at the site of entry and is associated with painful regional lymphadenopathy.
Glandular tularaemia – Similar to the ulceroglandular form except for the absence of the characteristic skin lesion.
Oculoglandular tularaemia – The organism enters via the conjunctivae, causing a unilateral, painful, purulent conjunctivitis with submandibular, preauricular, and cervical lymphadenopathy.
Oropharyngeal tularaemia – Via consumption of infected food/water, it usually presents with a sore throat, abdominal pain, nausea, vomiting, diarrhoea, and occasionally gastrointestinal bleeding from intestinal ulcerations.
Pneumonic tularaemia – Infection via inhalation of infected dust or aerosols, presents with a dry cough, dyspnoea, and pleuritic chest pain. Can further develop into pneumonia and adult respiratory distress syndrome. This form is rarely acquired naturally, usually requiring accidental exposure in a laboratory environment or potential Bioterrorism aerosol release.
Typhoidal tularaemia – Where infection enters the bloodstream and major organs. It can present with fever, chills, painful muscles, and lethargy, along with any of the other above forms of presentation.
The incubation period can be between 1 day and 3 weeks, with symptoms appearing 2 – 5 days after infection. Pneumonia and sepsis are most likely to be complications of Tularaemia when infected via aerosol/inhaled form. Through general infection (not of that in Bioterrorism aerosol form), the Type A bacterium has around a 5 – 7 % fatality rate in untreated cases.
As FT is a bacterium, treatment involves antibiotics and supportive care depending on how affected the patient is.
Viral Haemorrhagic Fever (VHF):
VHFs are caused by viruses from 4 distinct families: Arenaviridae, Bunyaviridae, Filoviridae, and Flaviviridae. The term “viral haemorrhagic fever” refers to a condition caused by the viruses which can affect many organ systems, damage the overall cardiovascular system, and reduce the body’s ability to function on its own. Symptoms of this type of condition can vary but often include fever and bleeding/haemorrhaging. Some VHFs cause relatively mild illness, while others can cause severe or life-threatening disease. Currently most VHF’s have no known cure or vaccine.
Although VHFs are caused by several families of viruses, these viruses share some common characteristics:
The list of VHFs is numerous, but some stand out for their potential to cause harm and fear in a Bioterrorism aspect such as the Marburg virus and Lassa fever. Ebola is also a VHF that is of concern for Bioterrorism which we will cover here in more detail:
A deadly VHF with high fatality rates, up to 90% in some recorded outbreaks. Ebola spreads through the body affecting the immune system and organs. It causes immune system disruption through numerous processes, such as infecting dendritic cells and interfering with their signalling to other immune cells, meaning that the virus has further time to spread without resistance. Ebola can also inhibit interferons, a molecule produced by cells to hinder further viral reproduction.
As the virus travels in the blood to new sites, other immune cells called macrophages consume it. Once consumed the macrophages become infected and release proteins that trigger coagulation which form small clots throughout the blood vessels and reduce blood supply to organs. They also produce other inflammatory signalling proteins and nitric oxide, which damage the lining of blood vessels, causing them to leak.
This process happens body-wide, causing significant damage, leakage of fluids, and haemorrhage. Death can be caused through multiorgan failure and hypovolaemic shock.
Symptoms can develop 2 to 21 days after infection, including:
As the disease progresses, it can cause bleeding inside the body, as well as from the eyes, ears, and nose. Patients may cough/vomit blood, or pass bloody diarrhoea. It spreads through contact with the skin or bodily fluids of an infected animal/person, and through contact with contaminated objects. A person is only infectious when they develop symptoms, not before.
Treatments for Ebola can help reduce the fatality rate, although it still remains significant. Monoclonal antibodies are a newly developed treatment which act like natural antibodies to stop the virus from replicating after it has infected a person. The Monoclonal antibodies can help reduce the fatality rate of the virus, although, further supportive care is required throughout the infection.