Coxiellosis in Africa
Dr Rick Last – BVSc, M.Med.Vet (Pathology)
Specialist Veterinary Pathologist
Introduction
Coxiella burnetti is a well-documented zoonotic
bacterial infection that causes Q fever in humans and
coxiellosis in animals. Various domestic and wildlife
animal species have been identified as sources of
human infection with parturient ruminants being
the most common source of disease in man. In
animals Coxiella burnetti is clinically associated with
reproductive disorders (abortion, infertility), but
frequently presents as a subclinical infection, while in
man Q fever is characterized by a febrile influenza like
illness.
Aetiology.
Coxiella burnetti is a gram-negative coccobacillus.
Classically it was considered a rickettsial agent, but
recent phylogenetic analysis suggests that Coxiella
burnetti is more closely related to the bacteria
Legionella and Francisella. The organism exists in
2 forms namely the large cell variant which is a
vegetative form found within infected cells, and the
small cell variant which is the extracellular infectious
form that is shed in milk, urine and feces and found in
high concentrations in placental tissue and birth fluids.
The small cell variant is resistant to heat, drying and
many common disinfectants and remains viable in the
environment weeks to years. Coxiella is considered a
potential bioterrorism agent due to its low infectious
dose, stability in the environment, ease of aerosol
dispersion and ability to cause substantial morbidity in
an exposed population.
Epidemiology and transmission.
Epidemiology is complex with 2 major patterns of
transmission occurring. In one the organism circulates
between wildlife and their ectoparasites (mainly
ticks) while the other occurs in domestic ruminants,
independent of the wild animal cycle. Infected ticks
may also act as reservoirs of infection. Distribution
of the bacteria is worldwide (except New Zealand),
with a broad host range including various wild and
domestic mammals, arthropods and birds.
The greatest risk of transmission occurs at parturition
by inhalation, ingestion or direct contact with birth
fluids or the placenta of infected animals. The
organism may also be shed in milk urine and feces
with transmission occurring through consumption
of these infected animal products. Ticks are also
capable of transmitting the disease amongst animals
but are not thought to play an important role in the
transmission of disease to people, although rare
incidents of tick transmission to man have been
reported.
Ruminants appear to be the major reservoir of the
organism worldwide. Infection is extremely important
in small ruminants, particularly goats, where it is
primarily associated with abortion or the birth of dead
or weak lambs and kids. In Africa camels are emerging
as an extremely important source of human infection
in certain areas of the continent. In 2014 a one health
systematic review into the epidemiology of Coxiella
burnetti in Africa, revealed that close contact with
camels was associated with increased seropositivity
amongst humans. There has been a dramati