Tularemia
Toss-up question: What communicable disease do these three creatures share in common?
Correctamundo! The deer fly (Chrysopsina), the deer tick (Ixodes Scapularis), and rabbit (Cuniculus) can all cause tularemia, though by somewhat different mechanisms of transmission. The dog tick (Dermacentor Variablilis) and the lone star tick (Amblyoma Americanum) can also carry tularemia. In the United States, almost 2,500 tularemia cases were reported to the CDC between 2011 and 2022, which averages to approximately 200 cases per year.
Let’s focus first on the deer fly. The subfamily Chrysopsinae is known as deer flies, perhaps because of their abundance where deer roam, and buffalo-flies, moose-flies and elephant-flies emanate from other parts of the world, where these animals are found.
Deer flies in the genus Chrysops are up to 10 mm (0.4 in) long, have yellow to black bodies and striped abdomens, and membranous wings with dark patches. As opposed to deer ticks, deer flies have very effective eyes, which enables them to fly during the day and target their prey for blood meals. FYI: Like ticks, the deer fly’s early relatives were likely present in the cretaceous period and parasitized cold-blooded reptiles, including dinosaurs.
Deer flies primarily acquire the bacterium Francisella Tularensis - a microaerophilic and fastidious gram-negative bacterium - by feeding on the blood of infected animals, especially rodents and rabbits. These animals are common carriers of the bacteria. Once infected, deer flies can transmit tularemia to humans through their bites. This transmission occurs when the infected fly bites a person, introducing the bacteria into the human bloodstream. Martha’s Vineyad has had at least one case of tularemia every year since 2000 C.E., but mostly through tick bites.
The deer fly infects more than 100 species of wild and domestic vertebrates and over 100 species of invertebrates. The most important vertebrates associated with F. Tularensis infection are rabbits and hares and rodents, as well as beavers, muskrats, squirrels and voles. Predators of the deer fly include nest-building wasps and hornets, dragonflies, and some birds.
Unlike tick bites, the deer fly’s bite is quite painful. The scissor-like jaws bite deeply into the skin, and saliva containing an anticoagulant stimulates a sudden inflammatory response.
A deer fly bite typically shows up as a raised, red welt with a small cut or puncture mark at the center. That center mark is the giveaway — deer flies don’t pierce your skin with a needle like mosquitoes do. Instead, they use scissor-like mouthparts to slice the skin open, then lap up the pooling blood with a spongy organ in their mouths. The bite wound can progress to an ulcerating nidus of inflammation The most common form is ulceroglandular tularemia. A skin ulcer develops at the fly bite site along with swollen lymph nodes, usually in the armpit or groin area. Other symptoms include high fever (up to 104°F), fatigue, and body aches, typically appearing three to five days after exposure.
Another method of acquiring tularemia is by way of pulmonary inhalation - seen especially on Martha’s Vineyard, where rabbits or rodents, infected with tularemia, die and then their carcasses are inadvertently aerosolized by mowing or landscaping equipment.
Tularemia pneumonia can appear on an X-ray as areas of lung inflammation, similar to other types of pneumonia, often showing increased opacity or whiteness due to fluid or pus accumulation.
Pneumonic tularemia is thought to be a possible germ warfare weapon - by introducing the tularemia bacillus into the ventilation system of an airport, infectious pulmonary tularemia could be spread to dozens of cities in a single day. Thus far, this has not happened, nor has person-to-person transmission of tularemic pneumonia been demonstrated or documented. In Europe, contaminated water has been shown to produce a form of tularemia, which often manifests with oral and pharyngeal inflammation.
Finally, tularemia can also be transmitted simply by the bite of a tick, which may or may not result in the ulcero- glandular form - causing fever, malaise, weakness, and potential severe sepsis and even death.
According to the CDC, “Francisella tularensis, the bacterium that causes tularemia, is highly infectious and can enter the human body through the skin, eyes, mouth, or lungs. Symptoms vary with the route of entry.”
“Tularemia is treated with antibiotics such as gentamicin, ciprofloxacin, levofloxacin, or doxycycline, depending on the infection's severity and the patient's condition. Treatment duration and choice may be adjusted for age, pregnancy, allergies, or underlying health issues.”
For some curious deer fly electron microscopy, I suggest Captain Corrosion’s website: