Disseminated cryptosporidiosis in simian immunodeficiency virus/delta-infected rhesus monkeys.

Abstract

Cryptosporidiosis has recently been recognized as a significant primary pathogen in animals and humans.s With emergence of acquired immunodeficiency syndrome (AIDS) in humans, there have been several reports of persistent diarrhea, fever, abdominal pain, and weight loss associated with Cryptosporidium infections, usually resulting in death.2.4.9 As of April 1986, 697 of the 19,182 reported AIDS patients (3.6%) had confirmed cases of cryptosporidiosis.8 Reports of cryptosporidiosis outbreaks in day-care centers and as the cause of traveler's diarrhea have increased awareness of this agent as the cause of disease in immunocompetent people as Recent studies on the development of an animal model for AIDS, using rhesus monkeys infected with Simian Immunodeficiency Virus (SIV), have been very promising. 1.7 Initial studies indicate that there are many similarities between SIV and the human AIDS virus, with parallel effects on the immune system of the host and similar opportunistic infections. Cryptosporidiosis has been reported in the gallbladder, biliary and pancreatic ducts, and intestine of macaques, prior to the discovery of SIV.3,6~10 All of the affected monkeys were infants or juveniles and had evidence of thymic atrophy, common in severely ill macaques (Blanchard and Baskin, personal observation), pneumonia, or gastrointestinal disease. We report here findings of four cases of cryptosporidiosis involving multiple organs (including the respiratory tract) in young rhesus monkeys experimentally infected with SIV/Delta at the Delta Regional Primate Research Center. The four affected rhesus monkeys were inoculated (at 7 to 15 months of age) with SIV/Delta, a retrovirus originating from a mangabey monkey. These animals were part ofa series of inoculation experiments in which 34 monkeys received SIV from various sources, including tissue from an asymptomatic mangabey monkey, lymphoid cells from a rhesus monkey with lymphoma, cultured virus pooled from several infected rhesus monkeys, and tissue culture derived virus isolated from a single rhesus monkey. Twenty-three of the 34 SIV-inoculated monkeys have died, 19 with opportunistic infections or lymphoma characteristic of the SIV-induced acquired immunodeficiency. Four of the 19 monkeys were diagnosed as having cryptosporidiosis after microscopic examination of tissue sections. The four Cryptosporidium-infected monkeys were necropsied immediately following euthanasia with an overdose of sodium pentobarbitol. Samples of all major organs were fixed in neutral buffered formalin and sectioned at 4-6 pm. Three random samples of small intestine (one each at the duodenum, the jejunum, and terminal ileum) and two samples of large bowel (one at the apex of the cecum and one at the mid-colon) were examined. Lesions were considered mild if cryptosporidial organisms were few in number and/or only a few inflammatory cells were seen. Changes were severe if numerous organisms (20 or more per villus) were present, if there was sloughing of the mucosa, and if 30 or more inflammatory cells per high power field were present. All four Cryptosporidium-infected monkeys died within 5 to 7 months after SIV inoculation with persistent or recurrent diarrhea and a combination of five or more of the following conditions: wasting, lymphoid atrophy, thymic atrophy, hepatitis, encephalitis, amyloidosis, bone marrow hyperplasia, glomerulosclersis, syncytial cell formation, and disseminated intravascular coagulation. Infectious agents included cytomegalovirus, adenovirus, Campylobacter, Cryptosporidium, Strongyloides, Candida, and Pneumocystis. All four monkeys died of a combination of several infectious agents, but cytomegalovirus, adenovirus, and cryptosporidiosis were the most severe. Two of the four monkeys had disseminated cryptosporidiosis involving the trachea, bronchioles, bile ducts, gallbladder, pancreatic ducts, and small intestine. Two other animals had small intestinal cryptosporidial infections ranging from mild to moderate that were segmental (present in some sections but not in others). Gastric and colonic mucosa were not involved in any of the four monkeys based on examination of one section of stomach and two sections of large bowel. Small intestinal changes were severe multifocal villus atrophy with synechia and moderate subacute inflammation of the lamina propria. The mucosal epithelium was flattened, especially in areas with high numbers of Cryptosporidiurn (20 or more per villus). The various stages of the organism were 4 to 7 pm in diameter, round to oval, and stained dark basophilic with pale centers. Organisms were primarily found on the mucosal surface, with occasional infected crypts in severely affected sections of small intestine. The associated mucosa had diffise moderate degeneration of epithelial cells with flattening and focal sloughing (Fig. 1). The lamina propria contained a moderate infiltration of plasma cells, lymphocytes, and macrophages. In addition, tips of villi had focal accumulations of pyknotic and vacuolated macrophages. A moderate number of crypts were infected with cryptosporidia and had a few sloughed cells and cell debris. A few crypts were hyperplastic and had several mitotic figures. Other changes associated with infectious agents, in addition to cryptosporidia, included lysis of cells due to cytomegalovirus and