H. Abbassi et al., Interaction of Marek's disease virus and Cryptosporidium baileyi in experimentally infected chickens, AVIAN DIS, 44(4), 2000, pp. 776-789
Histocompatible B13/B13 white specific-pathogen-free leghorn chickens were
used to investigate the effect of coinfection with Cryptosporidium baileyi
and the HPRS 16 strain of Marek's disease virus (MDV) in chickens and to as
sess the pathogenicity of C. baileyi when MDV is given before or after the
parasite. Groups of chickens concurrently infected with C. baileyi orally i
noculated at day (D)4 and MDV inoculated at hatching (C4M0 group) or at D8
(C4M8 group) were compared with relevant control groups inoculated with onl
y C. baileyi at D4 (C-4 group), only MDV at hatching (M-0 group) or at D8 (
M-8 group), and an uninoculated control group (UC group). The chickens were
kept in isolator units until the end of the experiment at D62. Our results
showed a considerable synergistic effect in concurrently infected chickens
and more severe consequences when chickens received MDV before C baileyi i
nfection. In fact, except for a slight transitory weakness, the chickens in
C, group remained free of overt clinical signs and there was no mortality
However, coinfection with both pathogens induced more lasting or permanent
oocyst shedding. Severe clinical cryptosporidiosis with weakness, anorexia,
depression, growth retardation, and chronic and severe respiratory disease
causing death occurred in all chickens in the C4M0 group between D12 and D
43 and in 67% of the chickens in the C4M8 group between D17 and D57. Eighty
-two percent and 33%, respectively, died before the development of specific
Marek's disease lesions. Mortality rates were 27% and 33% in the M-0 and M
-8 groups, respectively. The presence of MDV enhanced the establishment of
more lasting cryptosporidial infection in the respiratory trace, esophagus,
crop, proventriculus, and kidneys (only in C4M0 group) as well as in bursa
of Fabricius, ceca, and cloaca. Serologic analysis showed that chickens wi
th chronic cryptosporidiosis in the C4M8 group had an increased level of C.
baileyi-specific immunoglobulin A. Our results may explain some cases of m
ortality in chickens naturally infected with MDV and Cryptosporidium.